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Copyright © 1994-2007
Reproduction of this document in whole or in part is permitted if both of the
following conditions are satisfied:
1. This notice is included in its entirety at the beginning.
We will not be responsible for damage to equipment or property, your ego,
or personal injury or worse that may result from the use of this material.
Most problems with gasoline powered rotary lawn mowers as well as other
small engines have simple and inexpensive solutions. For example:
For electric lawn mower and other electric yard tool problems, refer to the
document: Notes on the Troubleshooting and Repair of
Small Household Appliances and Power Tools which includes chapters on
basic electrical theory (relax, no rocket science) and electric motor testing
and repair information.
We will deal with problems the weekend gardener is likely to run into
(sometimes, literally!) as well as semi-detailed overhaul instructions.
One or more of the books listed in the section:
References can be used to supplement this document
and can provide much more detailed troubleshooting and repair procedures.
Even if you don't know the difference between a carburetor and a crankshaft,
you may still be able to do some of your own work. (Hint: if you drop one
of these on your foot, the crankshaft will hurt a lot more!) We begin with
an introduction to small engine technology and have more-or-less separate
chapters on basic maintenance, intermediate troubleshooting and repairs,
and more extensive overhaul procedures.
I welcome comments, additions, hints, corrections, funny or other stories,
etc. As the title implies, it is oriented toward the gasoline engine powered
rotary lawn mower. However, much of the general information applies to a wide
range of yard and shop equipment powered by small 2 and 4 stroke gasoline
engines.
The following represent the basic precautions to take when performing
maintenance or service procedures on gasoline powered equipment and
dealing with gasoline in general:
Note: Modern mowers have at least two systems for stopping blade rotation
fairly quickly and keeping it stopped if the dead-man bar is released.
These will be either an engine kill and blade brake (on most inexpensive
mowers) or a blade brake/clutch which keeps the engine running but stops
the blade (on high-end machines).
Basic servicing of small engines doesn't require a $500 tool caddy. However,
some basic hand tools and other items will be needed.
A basic set from Sears (Craftsman) should be fine and will come with a
lifetime replacement warranty as well! If you have never invested in
a socket set, now is the time. Forget about those $4 specials, however,
as they are generally worse than useless. A word to the wise: you really
must have a socket set to do any kind of work on small engines. Slip-joint
pliers or worse yet - ViseGrips(tm) - just will not do!
While open-end or box-end (closed) wrenches may be used for certain bolts,
some simply are not accessible without a properly sized socket (like cylinder
head bolts).
Electric equipment is in some ways more environmentally friendly generating
no pollution (though the electricity had to generated somehow). Once the
equipment is unplugged, there is nothing to worry about with no gasoline to
store. Little maintenance is needed and there is never any issue of disposing
of used engine oil - since there is no engine oil. Electric equipment is also
usually - though not always - somewhat quieter.
The main disadvantage of line powered electric equipment is that it is
tethered to an electric outlet by the power cord. This can become quite
a nuisance after a short while. Battery powered equipment has tended to
less powerful and more finicky to deal with than similar equipment powered
from a line cord. And, electric mowers tend to be less powerful than similar
equipment using a small gasoline engine.
Where your yard is relatively small (say, less than 50 feet to an electric
outlet from the farthest point), a corded mower may be a good choice. It will
be less expensive than typical battery powered mowers and most gasoline
powered mowers, and virtually maintenance-free. Just make sure you use a
proper outdoor heavy duty extension cord - probably one size LARGER (lower
AWG wire size number) than what the manufacturer recommends. This will assure
minimal loss of voltage due to its resistance - and every bit of power you
have available will help! A somewhat lighter duty outdoor cord can be used
for the first few feet if that makes maneuvering the mower easier. The main
thing to watch out for is accidentally cutting the cord by running over it.
Mowing in a back-and-forth pattern while moving away from the outlet helps.
If you do cut the cord - don't panic. At most, you will need to shorten it a
couple of feet and install a new socket on the end of what is left AFTER
pulling the plug! If the outlet is now dead, at most you have tripped the
circuit breaker or GFCI, or blown the fuse. Of course if you make a habit of
this, your cord could get to be quite short. :-)
Battery powered yard equipment and power tools have improved greatly over
the years. Some of the newer models are quite capable of cutting a modest
size yard (e.g., 1/4 acre, manufacturers specifications may still be a bit
optimistic) on one charge with ample power for moderately thick grass.
But, there is quite a bit of variability in cutting performance and battery
life so shopping around, consulting Consumer Reports, and making sure you get
a return option if you are not satisfied are all well worth the effort - to
save effort in the long run.
It is interesting, however, that quite capable battery powered tractors for
example, have been around for a long, long time.
See the section: Comments on electric mowers for more
information.
Having said all that, the fact of the matter is that the vast majority of lawn
mowers used for modest or larger lots are gasoline powered.
Of course, if you have a postage stamp size or even a small suburban lot,
a manual reel mower may be your best choice - and you get some good exercise
as part of the deal as well.
Also see the comments in the Chapter "Items of Interest" on electric and
manual mowers.
Large mowers (those which carry you) may be of either the rotary or reel type,
usually gasoline or diesel powered but some electrics have been produced. For
information on riding mowers, lawn tractors, garden tractors and estate
tractors (also known as compact diesel tractors), see the
Small Tractor FAQ.
Consumer Reports regularly provides reviews and ratings of most common types
of lawn mowers. These articles are a good place to start as they include
a great deal of the basic information needed to decide on the lawn mower type
best suited for your property. They compare a selection of typical models
based on features, safety, price, and their tests of performance and operator
convenience. If you do not subscribe to Consumer Reports, your local library
will likely have access to several years of back issues.
For even more advice, see Consumer Reports Books' Yard and Garden Equipment
Buying Guide. It is sold at bookstores and newsstands and is also available
directly from Consumer Reports Books using the order form in the back of every
issue of Consumer Reports.
(From: Nigel Cowburn (nigel@hkem.com).)
"A neighbor of mine had a homemade car-battery-powered reel mower.
He used his actual car battery and worked out a mowing time that
allowed him to start his car again after mowing."
(From: Sam.)
I suppose he had to factor in the height of the grass to guarantee that
his car would start. :)
The uniformity, consistency, and just general appearance of a lawn mowed
with a rotary lawn mower is not quite up to the standards of that of a
professional reel mower. You will never get the perfect manicured look
though some models may come close. However, the simplicity, lower cost,
and need for less and more easily performed maintenance will generally
overcome the desire for perfection unless your lawn is featured regularly
in "Better Homes and Gardens" magazine.
Gasoline powered rotary lawn mowers are by far the most common type used
by homeowners and many professional landscapers as well. Most walk-behind
mowers use a manual recoil (pull) starter though electric start is available
on more sophisticated (and more expensive) models and generally standard
on riding mowers and lawn tractors.
The main disadvantages of a gasoline powered mower are the need to deal with
the handling and storage of gasoline and routine engine maintenance at the
end of the mowing season to assure easy starting next season and to prolong
engine life. However, most of this is pretty straightforward. See the
section: General preventive maintenance. Small gasoline
engines also do contribute to air pollution but new mowers must meet more
stringent EPA requirements as of September, 1996.
Electric rotary mowers are also available in both plug-in and cordless
(battery powered) versions. However, since gas mowers are generally more
powerful and not limited by the length of a power cord or charge of a
battery, they continue to dominate the market. Electric mowers are, of
course, non-polluting but the electricity had to be generated somehow.
WARNING: Never defeat the dead-man control for any reason unless there
is no chance of the mower starting.
WARNING: Rear baggers should never be operated without a bag unless the
opening is fully blocked or the proper deflector is installed. Grass
cutting performance will then be similar to that of a mulching or (side)
discharge type mower respectively but since this is a compromise, the
resulting appearance of the cut lawn may suffer.
Side discharge and bagging mowers can often be converted to mulching with
the use of a mulching kit which includes a means of blocking the discharge
port and possibly a special mulching blade. However, performance of one
of these may not be as good as that of a mulching mower since the airflow
requirements differ and these are largely determined by the design of the
deck.
WARNING: Most lawn mowing accidents result from reckless or careless use
of riding mowers and lawn tractors, not walk-behind mowers. These are not
as stable as an automobile especially when their large bags are full of
heavy, wet, grass clippings and may tip over on inclines that would not
be a problem with someone in control of a walk-behind lawn mower. They
are best and safest for use on large flat open lots. A walk-behind mower -
perhaps even a manual reel mower - should be used for sloping or irregular
areas and for mowing or trimming around obstructions like trees, shrubbery,
landscaping timbers, posts, fences, planters, boulders, and so forth.
Above all, understand the very important SAFETY information.
If there is some 'simple assembly required', take your time and follow
the instructions step-by-step. Despite the apparent efforts of the
designers of the mower and the manual writers to make everything as
obscure as possible, it will probably go together without undo difficulty
if you use the proper tools. With some, all you need to do is unfold the
handle taking care not to pinch any control cables - oops - and you are
ready to go to work. Happy times are here again!!
IMPORTANT: For 4 stroke engines, make sure there is oil in the engine!!!
Learn how to check it and fill it to the proper level if there is none or it
is low. See the section: Checking the oil.
WARNING: Running an engine without oil can ruin it in a few minutes and your
warranty will not likely cover such stupidity. Since the lawn mower may be
shipped without any oil, it is your responsibility to check this and then add
the proper amount of the correct type of oil to the crankcase!!!
For 2 stroke engines, special oil (not the usual 10W-30/40 type motor oil, nor
WD40 or 3-In-One!) must be mixed with the gasoline in the correct proportions
IN THE GAS CAN - not the fuel tank of the mower! See your users manual!
Forgetting to use the proper mixture can ruin a 2 stroke engine in a matter
of minutes and your warranty will not likely cover such stupidity. Adding the
oil to the fuel tank is not recommended because thorough mixing cannot be
assured.
If you have yard equipment with both 2 stroke and 4 stroke engines, clearly
label the two gas cans to indicate which equipment each is used in.
Note: Apparently using a 2-stroke gasoline mixture in your car may actually
cure some types of valve problems, at least temporarily. This is similar
to adding stuff like "Marvel Mystery Oil(tm)", but is probably a lot cheaper.
You didn't hear it from me though. :) In general, adding some 2-stroke
mixture to an automobile's fuel tank isn't going to cause any harm unless
it's a high concentration in a steady diet.
If the tank detaches easily as with many Tecumseh/Craftsman engines, just
lift it off and drain the gas into a gasoline safety can reserved for this
purpose. If the tank doesn't come off easily, I typically use a cooking
baster to do this (you know, the thing you use when baking turkeys!) although
the gas tends to destroy the rubber. There are similar devices or gas
siphons available at auto parts stores that survive better.
For 4 stroke engines, gasoline is used as-is since there is a separate oil
supply. For 2 stroke engines, you must mix the proper amount of the correct
2 stroke engine oil (outboard motor oil or whatever is recommended by your
engine's manufacturer). Fill your '2 stroke mixture' gas can with about
half the amount of gas you are preparing and add the proper amount of 2
stroke engine oil. Put on the top and slosh this around to thoroughly mix
the oil in with the gas. Then add the remaining gas to the total amount
for which your oil measurement was made.
How do you tell if a lawn mower you just inherited has a 2 stroke or 4 stroke
engine? The vast majority are 4 stroke - look for an 'oil filler cap'. On
many, this is clearly marked with words like 'oil' or 'oil fill' or with a
suitably ambiguous icon. Removing it will reveal a dipstick. (Note that
unlike the engine in your automobile, this is both the test and filler
location.) However, on more basic models, it may be near the base of the
engine and be unmarked. In addition, there will generally be markings as
to the need for the gas/oil mixture somewhere on the cover. The only major
manufacturer of lawn mowers I know of that has used 2 stroke engines in
recent designs extensively is Lawnboy.
If you are unsure of the correct mixture ratio - they typically range from
16:1 to 32:1 gasoline:oil by volume - 16:1 is probably a safe choice, though
newer engines will probably be safe with 32:1 or even higher. The
worst that can happen with too low a ratio is that the spark plug may
be more likely to foul (and you will pollute more than necessary) but
at least you won't risk damaging the internal parts from lack of oil.
It is of course best to determine and use the recommended mixture ratio.
(From: Mike's Small Engine (smallengineparts@yahoo.com).)
Today's manufactures are having to comply with the EPA standards for
small engine emissions. Although you will see gas:oil ratios as high as
40:1 or 50:1, it is perfectly safe to use a little more oil in your gas. For
each 1 gallon of gas, I would recommend 4 ounces of 2-stroke oil. This
translates to a 32:1 ratio. Since oil is added to the gas mixture to
lubricate and protect the internal engine parts, having a little bit
more oil will only help your 2 cycle engine last longer.
WARNING: When filling your gas can, place it on the ground a few feet
from your vehicle - never fill it inside the trunk or truck-bed. See
the section: Where to fill gas can.
However, a gallon of gas goes a long way with a walk-behind lawn mower. I
don't have exact numbers but a gallon will probably do several acres of
mowing (assuming you aren't chopping foot high grass!).
If you must transport gasoline in a vehicle, make sure the container is
secured in an upright position and tightly capped (both the filler spout
and vent openings). Provide adequate ventilation so there can be no
possibility of fume buildup in the trunk or passenger compartment.
Also see the section: Explosion risk when filling a metal
gas can.
(From: Joyce (joduren@ix.netcom.com)
Please be careful about filling the gas can. I saw something on one
of those PBS How to do it shows (or was it in the newspaper?) that
said that people are filling their plastic gas cans with them still in
their trunks or hatchbacks. They said this is dangerous because the
can isn't grounded or something and a static electricity spark could
make the thing to explode.
(From: Floyd Reed (floyda@ix.netcom.com).)
Being an old small engine mechanic from way back, I suggest that you don't
use any additives to keep your gasoline 'fresh'. Dispose of old gasoline
(end of season) by dumping it in the (nearly full) fuel tank of your car, then
refill your gas can at the beginning of the mowing season. It should last
you the season. With this method, you spend no extra on additives (that are
no good for an engine), you don't waste 'old' gasoline, and you don't dump
raw gasoline into the environment.
(From: Dan Weise (dan_yz@cin.net).)
I have found the commercial product Stabil the best thing since sliced
bread. It prevents the gasoline in the gas tank from gumming up. I'm too
busy to run around emptying gas tanks in the fall.
Instead, I shoot in a squirt of Stabil, run the engine for 5 minutes, shut
the gas valve off (unless it's a suction carb mounted on the gas tank) and
the engines start next spring.
That was *not* the case before Stabil. I can't count the number of times
I've disassembled a carb and sprayed Gumout trying to unclog the main jet
or the idle jet. Or had the float stick down and flood everything in
sight. All because of gummy gasoline.
I've used Stabil for about 10 years with great success.
I also use that Slick 50 teflon stuff, but have no idea whether it does any
good or not. But for the investment in an engine, I can't see that it
hurts. The intermittent duty of many engines makes them more vulnerable to
oil run-off than vehicles that are used daily.
In some cases, obstructions like tree roots cannot be moved. In this case,
you will either have to mow around them or raise the cutting height of the
blade to clear.
For the following, we will assume you pull a self-retracting starter rope.
With an electric starter, replace the words: 'pull...times' with 'crank for
several seconds'.
Move the mower or other equipment to the place where it will be used - no
sense in dragging a chugging lawn mower through the neighborhood. Position
it on a solid level surface. Make sure there are no loose stones, twigs,
branches, logs, etc. underneath to get sucked up and thrown about once you
succeed in getting the engine started (if you ever do).
When attempting to pull on the starter cord, it may be helpful to put one
foot on the mower deck to brace it. Whether this is needed will depend
on the design of your mower and in what direction the cord exits from the
starter.
You or the starter motor supplies the power to get it started. However,
at the low speed of starting, special modifications may be required to the
fuel system for the engine to catch. These may take one of the following
forms:
A typical starting procedure for an engine with a primer might be:
Automatic choke - temperature and engine vacuum control the fuel-air mixture.
A typical starting procedure for an engine with an automatic primer
or automatic choke might be:
A typical starting procedure for an engine with a choke might be:
If the appropriate procedure is not successful, the engine may be flooded.
You can give it 15 minutes or so for the gas to evaporate and try again or,
if there is an IDLE or LOW speed position, open any choke and pull the rope
several times in this position which should clear out the excess gas. Then
repeat the recommended starting procedure.
If none of this works, you may have a starting problem and should refer to
the section: Lawn mower will not start. Probably,
you forgot to fill the gas tank!
Where behavior seems to have changed, first confirm that environmental
conditions are the same and the gasoline is fresh before blaming the engine
on starting problems.
If the engine operates normally once started (assuming you can get it started
by some other means like squirting some starting fluid into the cylinder),
then dirt may have made its way into the priming mechanism. Disassembly and
cleaning may be all that is needed. However, there really isn't much to it:
Pressing the primer just pushes some air into the carburetor, which squirts
some gas via the main carburetor jet to the intake pipe. There really isn't
much that can wrong as long as the rubber primer bulb and connecting tubing
(if the primer isn't on the carburetor itself) is in good condition.
More expensive equipment will have a blade brake clutch meaning that while
there is still a dead-man bar but instead of killing the engine when released,
it disengages the blade (clutch) and brings it to a rapid stop (brake). This
is more convenient especially with a balky engine. There will then be a
separate engine stop switch - possibly combined with a speed/throttle control.
Equipment with an electric starter may have an ignition switch just like
an automobile and there will be three positions: STOP, RUN, START.
Some older equipment just has a stop contact that grounds the spark plug.
Pressing on a lever connects the spark plug terminal to the engine chassis
and kills the spark. While this is fairly reliable, it may be a momentary
contact meaning that the engine may be on a hair trigger and even rotating
the blade a fraction of a turn may cause the engine to take off again. Thus,
disconnecting the spark plug wire or removing the spark plug is even more
critical when working on this sort of equipment.
The most likely cause of such misbehavior is a stop wire that has become
disconnected or has broken. This is easily remedied.
Also see the section: Additional comments on winterizing -
draining versus the use of fuel a stabilizer. The use of stabilizer
is convenient but I think draining is preferred as it is safer not storing
garden equipment over the winter loaded with gasoline.
Then, when it comes time to start mowing again (yes, I know, you can't wait),
all you should have to do is add fresh gas (don't use last season's). The
mower should start on the first (well, maybe, second) pull. There may be
some white/blue smoke for a few seconds from it burning off the oil coating
on the cylinder walls but this should quickly disappear.
The Lawn-mower-shop.com Web
site has great deal of useful information including diagrams of popular
carburetors and links to small engine manufacturers.
Here is another recommendation:
(From: Bill Harnell (bharne@adss.on.ca).)
Change the oil at the *end* of the season. No need to leave the acid charged
oil in the crankcase over the winter to corrode the engine.
Then add a couple of teaspoons or so of Stabilit to the gas tank. Run the
engine for approximately 5 minutes and while you're at it, inject some fogging
oil through the carburetor to thoroughly coat all of the interior surfaces.
Directions are provided on the fogging oil container.
Wipe the frame and handle with an oily cloth and oil all pivot points
lightly. Clean the crud from under the deck - you do that frequently all
summer - right? Remove all the grass clippings from around the flywheel and
the cylinder fins.
Then store it in the shed or garage.
It will start on the first or second pull every spring.
BTW, you should be able to get both Stabilit and fogging oil at any reputable
engine service center.
The proper amount of oil is critical to the happiness of your engine.
Too little and it may overheat, cause excessive wear, and in extreme
cases (but not unusual), cause engine parts to seize and fail - very
expensive. Make it a habit to check the oil regularly. Doing this after
about every 5 hours of operation is generally recommended. More frequent
checks - such as before each time you mow - are fine as well. A typical
small engine in reasonably good condition does not use up a lot of oil but
checking oil is easy and will not hurt.
Oil should be checked when the engine is cold or after waiting 10 minutes
for it to drain back into the oil sump after running the engine.
If the oil level is high - you just bought the lawn mower or were careless
in filling it last time - drain enough oil to bring the level back down to
the full mark. Too much oil can result in problems as well - oil spraying
out of various orifices or getting into other places where it should not
be like the combustion chamber.
If you find the oil level over the full mark or higher than it was before,
gas may be leaking into the oil due to a flooded carburetor - a stuck inlet
needle or bad float. If this is the case, the oil will need to be changed
once the underlying cause of the leakage is determined. (This is only likely
with float type carburetors such as those used on the Tecumseh engines used in
a variety of Sears/Craftsman models equipment.
If the oil is very low and you have been performing regular maintenance, there
may be a leak or your engine may need a ring job. Excessive oil under the
deck - on the shaft or blade adapter - would indicate a bad bearing or oil
seal. Noticeable blue smoke while running would indicate that excessive oil
is getting by the rings into the combustion chamber.
Typical oil capacity is just over 1/2 quart (usually about 1-1/4 pints).
The capacity of a typical small engine is just over a 1/2 quart. This will
probably cost you about 50 cents - a very worthwhile investment!
However, some people do swear by synthetic oil. I remember it worked pretty
well on my bicycle as well :-):
(From: Daniel Pope (dpope@l-a-net.net).)
Synthetic Motor Oil in the crankcase and Marvel oil in the gas is the only
way to go!
I have a $1,900 MTD tractor style mower with B&S engine (L head twin). It has
over 800 hours and 9 years on it and I mean rough hours (bahaya grass and hot
weather). The engine does not use a drop of oil (changed every 30 hours) and
the compression is the same as when new. These other guys can have there
$5,000 fancy mowers. I'll use that money to buy a truck.
Since there is typically no oil filter, all the grit, metal particles, and
other undesirable stuff continues to circulate with the oil to find its way
in between precision engine parts.
For small engines, the oil change interval is usually specified to be
about 25 hours of use. More frequent oil changes may be desirable if
the equipment is operated in an extremely dusty environment.
A typical mowing season for a modest size lot is around this amount of
time so an oil change once a season is probably satisfactory. I recommend
this be done at the end of the season so that the old contaminated oil
does not sit in the crankcase during the winter months and you will not
(conveniently) forget to do this at the beginning of next season when you
are eager to get at that straggly lawn.
First, drain the gas or remove the gas tank. If you will be filing steel,
you get sparks. Sparks are not the greatest thing to have around gasoline
vapor. Enough said. Disconnect the spark plug wire and tie it safely
away from the spark plug or remove the spark plug entirely. Turn the mower
on its side.
CAUTION: Immediately check for oil leaks at the oil filler pipe or elsewhere.
If there are any, you will need to work on the mower just propped up by 45
degrees or so. Or, use this as a good excuse to perform an oil change and
drain the oil (even if the engine is cold, most of the oil will drain out but
it will take a little longer). Just don't forget to refill the crankcase with
fresh oil once you have completed work on the blade!
Check that the blade isn't bent. Locate a reference point on one side
and note the height of the blade tip at that location. Rotate the blade
180 degrees and check the height of the opposite blade tip. There should
be no significant difference - say no more than 1/8" or so. If it is greater,
the blade is bent or the crankshaft is bent. Either will require further
investigation as running the mower under such conditions will probably result
in excessive vibration and can be dangerous.
Assuming this is fine, inspect the blade:
Slight nicks and dents can be cleaned up with a file while the blade is
still installed on the mower. Unless you have run into a curb, this is
probably all that is needed on an occasional basis. Removing this small
amount of metal will also not unbalance the blade enough to worry about.
Refer to the section: Non-violent blade removal if
it needs to come off the mower.
If the damage is severe, consider replacing the blade entirely - they
are not that expensive (usually under $10). Otherwise, you can use a
file, a bench grinding wheel, or a grinding wheel mounted in an electric
drill (there are special attachments for this specific application).
Since the rotating blade also contributes to the proper air flow, you do
not want to upset the shape. Grind in such a way that the original blade
angle is preserved. It doesn't need (or want) to be razor sharp. A 1/64"
edge is fine. Anything finer will quickly be dulled by little bits of stone
and dirt in any case. Safety is not the main concern here - if any part of
your anatomy contacts the whirling blade, you **will** be in trouble no
matter how dull or sharp the blade might be!
Attempt to remove approximately equal amounts of metal from both ends and
in roughly similar areas if possible. If there are a few large nicks, it
isn't necessary to remove them completely - your lawn (and neighbors) will
never know the difference.
Check the balance by positioning the blade at the center hole location on a
pencil or other rod - you don't need a fancy blade balancer but can use one
if you like. If it tips one way or the other, remove more material from the
heavy side a little at a time.
Replace the blade along with all its mounting hardware. Make sure you get
all parts in the same relationship as they had originally. The blade must
have its sharpened edges pointing downward. Don't forget the install the
key if it is separate and DO NOT substitute a hard steel key for the soft
metal one that should be used. See the section: Why soft
metal keys must be used. If the locking key or blade adapter key appear
damaged in any way, replace it.
In either case: disconnect the spark plug wire and tie it safely away from
the spark plug terminal (several inches minimum) or remove the spark plug
entirely to prevent accidental starting.
If the nut holding the blade on is just on very tight, use a block of wood
to prevent the blade from turning. Use a good quality socket wrench or
box-end wrench of the correct size - an adjustable or even open-end wrench
may not be enough. The nut usually unscrews counter-clockwise. However,
check this out first! A careful inspection of the threads on the end of
the crankshaft will reveal the direction. Or, determine the direction of
rotation which will be designed to tighten, not loosen the blade. Most,
if not all, single blade mowers rotate the blades clockwise as viewed from
above which will therefore use a normal right-hand thread nut.
CAUTION: Make sure that if the wrench slips, your flesh will not contact the
blade or other sharp sheet metal - liberal use of rags or newspapers is a
good idea. Arrange your position and the mower so you are pulling towards
you - this is a more stable controllable arrangement.
(From: Graduate student of school of hard knocks.)
Use some penetrating oil (e.g., liquid wrench or WD40) on the nut and
threads if there are signs of rust or corrosion. Allow it to soak in
for a few minutes before attempting to remove the nut.
You will prevail. A hammer or other more violent approaches should not
be needed.
Once the nut is loose, unscrew it the rest of the way by hand and remove
any washers or mounting plate and note their exact position and orientation.
The blade and adapter should come off easily. Some penetrating oil (e.g.,
WD40) may help if it is difficult to remove.
If your adapter/blade doesn't pop off after removing the nut or bolt, it may
be mounted using a taper like the flywheel. This is somewhat unusual on a
walk-behind lawn mower but might be present on a larger machine like a lawn
tractor. A wheel puller is best for dealing with this situation but first
see if it isn't just gummed up or rusted in position - try the WD40.
Inspect the key or locking tab for damage. You may have:
If the adapter's tab is broken off or the key is sheared or damaged, then
replacement of the entire blade adapter or just the key (depending on your
mower's design) will be needed upon reassembly. For now, if you will be
sharpening the blade, replace all the hardware in the correct positions
(except the blade) and finger tighten the nut so you won't lose anything.
WARNING: Do not install a hard steel key in place of the recommended blade
lock key as you will lose the protection that the soft metal provides and
the next incident may be the last... See the section:Why
soft metal keys must be used.
Once you have reground the blade or obtained a replacement, reassemble in
reverse order and then tighten the nut to the proper torque.
(From: Gib Gahan (gahan@esinet.net).)
Another way to remove a stubborn blade is to take it to your friendly garage
or tire changer and have them put an impact wrench on it. Saves knuckles,
tempers, etc. Just don't put the blade back on without a touch of oil or
anti-seize compound and of course, don't use an impact wrench!
For adjustable types, it is best to refer to your engine manual. However, here
is the general procedure. Some of the specific numbers may differ for your
engine, however.
In all cases, before touching any adjustments, make sure your air filter is
in place, and clean (or new). Fill the fuel tank about half full with fresh
gasoline.
There are three adjustments on a typical carburetor:
Initially, carefully and gently turn the two mixture controls in until they
just seat.
Note: "In" means clockwise (the way you would tighten a normal screw) and
"out" means counterclockwise (the way you would loosen a normal screw).
CAUTION: do not force them - you are not trying to tighten anything - as you
will damage the needles and seats which will require replacement of the
needles or entire carburetor. Then back them out 1 to 1-1/2 turns. Set the
idle speed screw 1 to 2 turns beyond where it contacts the throttle plate.
Refer to your engine manual for specific recommendations! These settings
should allow the engine to start and run, though perhaps not entirely smoothly
or with great enthusiasm.
WARNING: if in doubt, set it low. It is better to end up with a scraggly
lawn than bodily injury or a blown engine! Note that by ear, 2 stroke
will always sound faster than 4 stroke engines for the same output
speed because they have twice as many explosions per rotation of the
crankshaft!
(From: (Willjim@gte.net).)
Once the air filter is saturated it must be wrung out. I typically place them
in a paper towel and squeeze. Then possibly a second paper towel. No oil
should be dripping out of the filter when gently squeezed. Chilten's B&S
engine section says to simply squeeze the filter of excess oil - no mention of
a paper towel, etc.
In adjusting the carburetor, Chilten says about 1-1/2 turns but 2 turns is my
standard.
I get the engine running first - warm it up to general operating temp. No
applied choke, air cleaner installed. Adjust the main jet if you can get it
to run at rated speed - preferably under load (turn in to the lean studder,
out to the rich studder then back in about 1/2 way between these extremes).
Then adjust the idle, at idle - at no load - using the same operation as the
main jet. You may then go back and repeat/refine the process a second time
as the idle adjustment may affect the main a bit.
For the 92000 in particular (typical but refer to your specific engine model
for exact specifications), from Chilten's second edition, "Repair & Tune-Up
Guide for Small Engines" (successor to [2]):
Since an automobile engine spark plug fires on every other revolution of
the crankshaft rather than every revolution as with most single cylinder
2 and 4 stroke engines, it will probably be necessary to multiply the
reading by a factor of 2. (Even though there is a power stroke every other
revolution for the 4 stroke engine, the ignition system is usually active on
every revolution. However, there are a few exceptions to this rule.)
For equipment where a shaft with a known speed ratio to the engine crankshaft
is available (i.e., a power take-off or trimmer head), an optical stroboscope
of one form or another may be used. You will just need to paint or tape some
stripes on the rotating part to put under strobe illumination:
For example, for something like a string trimmer which has a direct coupled
hub, strobe disks with 2, and 3, and 4 radial lines will appear stationary
under fluorescent illumination for 3,600, 2,400, and 1,800 RPM respectively.
There can be ambiguity but if you are already in the ball park, this sort of
approach may be all you need.
(From: Philippe Habib (phabib@netcom.com).)
Go to a hobby shop that sells radio controlled airplanes. Plunk down $30 or
so and get an optical tach. Paint 2 strips on the (crankshaft) hub of your
equipment to simulate a propeller, and you're done.
(From: J. Matthew Good (jmg14213@ix.netcom.com).)
You shouldn't need a tachometer on a trimmer. Two stroke engines in the size
and power range of line trimmers can't overspeed as they don't have the power
with a line head installed. Just set the carburetor up so that it 'two-fours'
at wide open throttle and you should be all set. If it needed to be adjusted
with a tachometer, it would have some kind of governor on it.
(From: Mowerman (mowerman2687@my-dejanews.com).)
B&S engines have a spring in the governor arrangement. You want to change
tension on the spring to change the speed. (This is basically true of most
other small engines as well but the details will differ.) The spring is
attached to a metal tung (strip) in the linkage at front of motor, this is
made of a tinny metal so you can easy bend this tung. To lower speed you
want to lessen the tension on the spring. You can do this while the motor
is running at top speed but it would be safer to do the bending while mower
is not running. By pushing in tung you will lessen top speed gently as it
doesn't take much to alter that speed. Often this tung gets knocked in
while mowing around bushes or other protruding material and "hey presto"
your engine is only idling. It is a design problem that briggs should be
working on, however I love B&S engines with their simplicity and ease of
maintenance.
(From: foxeye@www.compumise.com).
I would start with them both backed out from the closed position to 2 turns
open, for starters. One should be idle mix and the other should be high
speed. Crank the motor, get it warmed up. You may have to fiddle with the
throttle and or choke until its warmed up. Then slowly turn in the low speed
jet, until it starts to die, then back it out another 1/4 to 1/2 turn. Then
hold the throttle wide open, and slowly turn in the high speed, until it
really starts to smooth out and rev high, and start screaming, then back this
out until it starts to run rough or slow down, and then turn it back in to
midway between these two positions. Keep playing with the low speed needle
until you get rapid immediate response from the throttle, and good idle with
the idle adjustment. Then play with the high speed needle, but always back it
out from the setting about 1/4 turn or so, from where it runs the
smoothest. This setting of backing it out will allow more fuel when under a
load, and keep your 2 cycle motor from running too lean. Put a load on it and
just tweak the settings just a hair at a time. If you're in the ball park it
won't take much adjustment either way to make a difference. Better on the rich
side than lean side. Also make sure your oil / gas is mixed at the proper
ratio. 99% of 2 cycle motors are adjusted the same, no mater what brand they
are. Most will start and run with both screws open 2 turns initially. Just
don't close the high speed off any more than necessary no matter how well
it runs.
While this chart lists many problems, it is does not cover everything that can
go wrong. However, it can be a starting point for guiding your thinking in
the proper direction. Even if not listed here, your particular problem may
still be dealt with elsewhere in this document.
(Portions of the following from: Chilten, Small Engine Repair 2-12 HP, (1).)
Note that the assumption here is that it cranks - the crankshaft and blade
rotates in a normal manner but the engine never catches. Some larger (Briggs
and Stratton) engines may have a low-oil cutoff switch which will stop the
engine if the oil level is inadequate. However, this is not likely on a
push mower.
If you are unable to pull the cord (or the auxiliary starter on one with
electric start), there may be a clump of grass stuck between the blade and
the deck or there could be serious internal damage, especially if you just
encountered an immovable object. See the section: Lawn
mower will not start after the blade hit an obstruction. However, you
didn't forget to engage the dead-man bar, did you? On most inexpensive mowers
this safety interlock is needed to both enable the ignition system and release
the blade brake.
(From: Mike's Small Engine (smallengineparts@yahoo.com).)
Nowadays, a lot of mower/equipment is using OHV (OverHead Valve)
style engines. This in itself causes many starting troubles.
These engine use a compression release on the camshaft
to allow for easy starting. Once the engine has
started and reaches a speed of over 700 rpm, the weight
on the compression release swings out and allows the
engine to gain full compression and full power. After
awhile, the valve lash/clearance begins to widen and
the first thing that goes wrong is the compression
release doesn't work properly causing the engine to
drag which may sound to some as a dead or dying
battery. I'm sure there are untold thousands of people
that have replaced batteries, solenoids, starters,
switches, etc., only to find themselves going to a
repair shop and letting a trained mechanic do what is
a simple maintenance adjustment.
Once you have exhausted these obvious problems, determine if gas is reaching
the cylinder as follows: Perform the normal starting sequence and then,
assuming it shows no signs of wanting to start, immediately remove the
spark plug. If fuel is reaching the cylinder, the spark plug should be
damp with gas and there should be a very distinct odor of gas from the
spark plug hole. If there is none, then there could still be a blockage
in the fuel line or the carburetor may need cleaning.
A flooded engine, most likely due to extended unsuccessful attempts at
starting or a defective carburetor (float valve stuck open or gas-logged
float) will result in inability to start as well and a distinct odor of gas.
You might find raw gas coming our of various orifices - air filter as well
as exhaust. (Note that in severe cases, enough gas gets mixed in with the
oil to significantly increase the level in the crankcase and reduce the
effectiveness of the oil. This will require an oil change.
To much air results in a mixture that is too lean, burns too quickly, and
can result in engine damage over extended periods of operation.
Too little air results in a mixture that is too rich - there will be loss of
power and possibly black smoke from the exhaust. This could be due to
several factors:
WARNING: make sure there is no gas in the vicinity when performing the
following test!
Remove the spark plug wire and insert the blade tip of an appropriately sized
and well insulated (plastic) screwdriver inside the boot or clip in place of
the spark plug. While holding the *insulated* part of the screwdriver,
position the metal part of the blade about 1/8th inch from the block or frame.
An alternative technique is to use an old, but good, spark plug whose gap
has been increased to about 1/8 inch or one specially made for exactly this
purpose. In this case, simply connect the spark plug wire to the test plug
and hold its threaded part against the cylinder head or other part of the
chassis (away from the gas tank!!).
Note: Just positioning the spark plug wire a short distance from the spark
plug terminal is not recommended as the results of this test will then depend
on the condition of the spark plug as well since the spark will have to
jump two gaps.
Have a buddy crank the engine at normal starting speed so that you will be
able to hold the screwdriver or test plug steady and be close enough to see
any spark clearly. Shield the gap from the sun or bright light if necessary.
You should see a nice healthy spark jump the gap several times on each pull
(actually, once per rotation of the crankshaft/blade on both 2 and 4 stroke
engines). Note: 4 stroke engines ignite the air-fuel mixture on every other
rotation of the crankshaft. The extra sparks fire harmlessly into the exhaust
gasses and are wasted. Can you believe it?!
CAUTION: if you are not well enough insulated, *you* will jump several times
per rotation of the crankshaft/blade if the ignition system is functioning
properly! Hey, that *is* a valid test!
If this test confirms the spark, it is still possible that the spark plug
is fouled or bad. See the section: Checking the spark
plug.
If there is no spark, then there is a problem with your ignition system.
However, a number of other problems can result in lack of spark:
Make sure stop switch/stop wire is in appropriate position - confirm with a
multimeter, check that flywheel is being spun by starter and that flywheel key
is intact to assure proper timing, check condition of points/condenser and
setting (if applicable), test magnet (on flywheel) for strength, check the gap
between flywheel and magneto core. If these are all fine, test or replace
the magneto.
In more detail:
Items (2) and (3) are likely if your just attempted to move a curb with
your mower blade (or if someone inadequately tightened the flywheel nut
during some previous maintenance).
See the section: Testing the magneto.
First, check that the dead-man bar is properly disengaging the stop switch
when pulled and/or throttle control is properly disengaging the stop switch
when in the start or run position.
For anything beyond this, disassembly will be needed to identify and replace
any defective parts.
If the no-spark condition happened after the blade hit an obstruction,
(1) or (2) are likely. See the section: Lawn mower will
not start after the blade hit an obstruction.
The best thing to do at this point is just replace it with a new spark plug
and worry about the old one later. Actually, nearly every small engine
maintenance book will recommend changing the spark plug every season anyhow.
In an automobile, the battery supplies the primary current; in a magneto, the
magnet on the flywheel moving past the core at high speed acts as a generator
and induces current in the primary.
As the magnets spin past the pole pieces of the magneto core, the points are
closed and current builds up in the low voltage winding (and flux builds up in
the core). At or slightly before Top Dead Center (TDC), the current (and flux)
should be maximum and at this instant the points open. The flux then collapses
(and the condenser (capacitor) across the points acts as a snubber allowing the
current to bypass the open points and preventing arcing at the point contacts).
This rapid decrease in flux results in coupling of the stored energy to the
turn high voltage winding and results in up to 10,000 V or more at the spark
plug.
(For EE types, this is somewhat similar in basic operation to the flyback
converter in a switchmode power supply except that the moving magnet supplies
the input power instead of the rectified AC line and the points act as the
switch instead of a power transistor.)
The secondary will always be accessible for testing but the primary of an
electronic ignition may be not be due to the electronic components:
Wires can break due to corrosion or vibration. This would result in an open
winding - infinite resistance. Shorts can develop between adjacent windings
or to the core. This may be detectable as reduced resistance but without
knowing exactly what it should be, there is no way of knowing if a slight
discrepancy represents a problem or just slight variations in design or
manufacturing.
A more complete test would involve checking the 'Q' or doing what is called
a 'ring' test and even more for an electronic ignition. This requires special
equipment. Therefore, it is best to swap in a known good unit. They are not
that expensive.
Timing is set on older mowers with point type ignition systems by adjusting
the point gap and generally only changes due to wear. However, these changes
are gradual and unless the points come loose for some reason, will not likely
suddenly prevent the mower from starting. On newer electronic ignition
systems, there is basically no adjustment as the position of the electronic
ignition coil/module fully determines ignition timing and this is fixed.
However, timing can be grossly messed up if the flywheel key gets sheared
and the flywheel then rotates a fraction of a turn on its mount on the
crankshaft. The result may be a mower that does not start, backfires or runs
erratically, lacks power, won't run and/or start when hot, etc. This is very
likely to happen should the blade strike a rigid object causing the mower to
stop instantly. In this case one or both of the blade lock key and flywheel
key have sheared to (hopefully) protect the very expensive internal parts from
damage.
There are likely not going to be any timing marks for that old timing
light you have sitting gathering dust somewhere. The only test really
is to inspect the flywheel keyway to determine if damage has occurred.
See the section: Lawn mower will not start after the
blade hit an obstruction as this is the most likely cause of a sheared
flywheel key.
The assumption is that the engine started and ran normally prior to
the incident. Now, no matter how many times you yank the starter rope
or run the electric starter, it will not start at all, bucks, kicks back,
backfires, or fails to develop enough power to keep going on its own.
If the blade struck a solid boulder while the engine was set on 'high',
more severe damage is possible as even with soft metal keys locking the
blade and flywheel to the crankshaft, the inertia of the rotating blade
is acting sideways against the crankshaft in addition to suddenly stopping
its rotation. This can result in a bent crankshaft. The end of the
crankshaft with the blade adapter could be bent without affecting the
bearings or internal parts. This would need to be tested for as well.
Not that such an occurrence is that much better - the crankshaft would
still have to be replaced but at least the bearings in the crankcase
will not be damaged.
If the starter will not turn the crankshaft (assuming you remembered in
your haste to engage the safety bar) - it is seized or will only rotate
part of a revolution before hitting against something solid inside - then
you probably have serious internal damage that will require a complete
strip down and replacement of some (expensive) parts. If it turns but
much more tightly than you recall (assuming you do have the safety bar
engaged!) then the crankshaft may be bent - again very expensive. Repair
may not be worth it.
However, in most cases, what has happened is that either or both of the blade
lock key and/or flywheel key have sheared to protect the crankshaft from
serious (and terminal) damage.
If the blade lock key broke, the blade will no longer turn rigidly with the
crankshaft and provide the inertia required by many small engines with
undersized flywheels. In this case, the engine may try to start but die
out with a few "putt-putts" or even kick back on the starter cord. (As a
side note, attempting to use a lawn mower engine as a replacement on a
piece of equipment that doesn't have something to substitute for the blade's
inertia may not work for this reason.)
If the flywheel key broke, the ignition timing will likely be totally wrong
and the result may be no ignition, backfiring, kickback, or weak or total
loss of power.
To diagnose, proceed as follows:
First, pull off the spark plug wire and tie it securely away from the spark
plug terminal (several inches minimum) or remove the spark plug entirely so
that there is no chance of the engine accidentally starting. Even though it
will not start now no matter what you do, the underlying problem could
actually be a flooded carburetor or something else which may correct itself
while you are working. Never take chances.
Drain the gas or remove the fuel tank. This will prevent gasoline from
spilling out the gas cap vent hole or flooding the engine through the
carburetor since you will need to tip the mower to get underneath.
Set the mower on its side (carburetor side up).
CAUTION: Immediately check for oil leaks at the oil filler pipe or elsewhere.
The mower can usually be set on its side for a few minutes without harm but
if these occur - you will have to work with it tipped less than 45 degrees
or so - propped on wood blocks. Or, use this as a good excuse to perform
an oil change and drain the oil (even if the engine is cold, most of the oil
will drain out - it will just take a little longer). Just don't forget to
refill the crankcase with fresh oil once you have completed your work!
Using an old rag and/or proper work gloves, grasp the blade and attempt to
rotate the blade and crankshaft.
CAUTION, despite your lack of maintenance, the blade may be sharp!).
The blade and crankshaft should rotate together. If there is slippage, the
key has broken and will require replacement of just the key or the entire
blade adapter plate depending on design. If it appears to be intact, then
you can assume the flywheel key has broken. The blade key may be broken
as well but it is not likely the reason for your failure to start. You
should remove the blade to determine this for sure before restoring the
mower to service in any case. See the section: Non-violent
blade removal.
You can possibly avoid removing the flywheel for inspection of the key by
unscrewing the sparkplug, rotating the crankshaft so the piston is at TDC, and
noting the location of the magnet on the flywheel relative to the magneto
coil pole pieces. The magnet should be pretty close to the magneto in that
position. If this is not the case or just to be sure, the flywheel will have
to come off to inspect and possibly replace the key.
To get at the flywheel key itself, some disassembly is required.
You should now see the top of the flywheel. In most cases, a large nut
fastens the flywheel to the crankshaft. (However, in some designs, part
of the starter mechanism is actually used and this is supposed to require
a special wrench to remove. However, using a piece of wood as a buffer
and tapping the ears in a counterclockwise direction will work also. Refer
to your engine manual for details.) Use the proper socket to loosen this
nut (counterclockwise). It may be necessary to brace the flywheel securely
to gain enough leverage. Make sure this is done against something that can
stand the force. Once loose, remove it by hand and then remove any washers
or other parts that are under it. Make a note of how these were positioned
including which side is up on some cupped washers.
You should now see the keyway. The slots on the crankshaft and flywheel
should be aligned. There are two common types of keys:
You may even find that the flywheel is relatively loose on the crankshaft
if rotating the blade while holding the flywheel stationary is possible.
Either the blade key or the flywheel key or both are broken in this case.
You will have to remove the flywheel to replace the key if it is broken or
damaged.
If the flywheel is loose at this point, then the following will not be
needed as it can be lifted off.
There are several approaches to flywheel removal:
Bolts are screwed into holes in flywheel. Then, plate bears against the
flywheel nut (slightly loosened) and the nuts are tightened alternately
until the flywheel pops off.
WARNING: do not use an ordinary gear, clutch, pulley, bearing, or other
puller unless this is specifically mentioned as a recommended technique
in your engine manual. The flywheel could be damaged - possibly not
immediately obvious - but the result could be catastrophic failure once
the engine is put back into service.
(From: Foxeye (foxeye@www.compumise.com).)
The square shaft which turns one direction but not the other is the recoil
starter pawl. This can be pulled straight up from the round cup that it sits
in. There should be a couple of steel balls inside. Some models have a large
internal snap ring that holds this in the cup. Remove ring, and pull it
straight up. Use a magnet to remove the steel balls. Once you have this
starter pawl removed, and the steel balls, hold the flywheel, stationary, and
using a block of wood, bump one of the lugs on the outside of the starter cup
in a CCW direction.
Once you break it free of its torque, it should be able to be spun off
CCW. Remove this starter cup, and the beveled bellville washer under it. Now
your ready for your flywheel puller. A strap wrench can also be used to turn
this starter cup loose. When installing the starter cup, make sure it is clean
and free of grease and oils. A drop of oil or a light coating of grease on the
crankshafts stub end (over which the starter pawl goes) is usually
recommended. The starter cup only needs to be snugged down, and you don't have
to go overboard trying to torque it to ungodly tightness. Snug is sufficient.
Drop in the starter pawl, into the cup over the stub of the crank, and drop in
the steel balls, replace larger flat cover over this assy, and insert snap
ring if there was one.
Assuming there is no serious damage, a new flywheel key should be all you
need - about 25 or 30 cents. To confirm that this is all you need, replace
the flywheel without the key but line up the two slots as they would be
if a key were present. Tighten securely (but it doesn't need to be to
the full torque as this is just a test). This should permit the mower to
start and run normally but I would not recommend using the mower to actually
cut grass until you replace the flywheel key.
To install the new one, insert the key into the slot in the flywheel first
and then slip the entire affair onto the crankshaft (I like to use a bit
of WD40 for protection as well). The flywheel should seat securely with no
detectable free play - it should be on straight and not rock back and forth
at all. If this is not the case, the key may be in upside-down or there may
be something or some particles of dirt or metal blocking it. Replace the
washers, dirt screen, etc., and then hand thread the flywheel nut as far as
it will go. Tighten to the specified torque (typically, 30-33 ft-lbs).
Note: There may be a cupped washer between the nut/screen and flywheel.
This must be installed cupped-side facing the flywheel or else you will be
probably be replacing the flywheel key again very soon :-(.
WARNING: Do not install a hard steel key in place of the recommended flywheel
key as you will lose the protection that the soft metal provides and the next
incident may be the last... See the section: Why soft metal
keys must be used.
Then, replace the shroud, fuel tank, etc. If head bolts had to be removed,
it is probably a good idea to slightly loosen all of the head bolts and
then retorque them to the proper value in the recommended sequence for
your engine.
Note that the soft metal flywheel key can also be damaged without totally
shearing which may result in slightly incorrect timing. Symptoms may include
a mower that is hard to start, runs rough or lacks power, or cannot be
restarted when hot. Therefore, always replace the key if there are any signs
of damage or wear.
There can be numerous reasons for the engine to quit running when it
gets up to operating temperature.. expansion of metal parts where
bolts/screws aren't tight enough, breakdown of the condenser for the
ignition points (if equipped), or a possibility of a crack somewhere.
An overall inspection of the tightness of fasteners would be a good place
to start.
(From: Walt Conner (jerrbear@midwest.net).)
As soon as the engine shuts down, turn the flywheel by hand or DISCONNECT
the plug wire and turn the blade by hand to see if there is any
compression. I have had several B&S engines that did not have enough valve
clearance and when hot, the valve stem expands in length enough that the
valve does not properly close. After cooling, engine will be OK. Also could
be a bad condenser or the other faults listed above.
(From: Michael Stevenson (mike@gi4xsf.freeserve.co.uk).)
Problems with the ignition coil can make an engine impossible to start when
warm (or even stop running when it warms up), apparently this happens on
motorbike engines quite often and is caused by a break in the HT coil.
A carbon track forms inside the coil where the wire is broken. When the
engine is cold the carbon track has a low resistance and it conducts well
enough so the spark is strong enough to start the engine, when the engine is
warmer the track resistance is greater and the spark less strong. This
problem gets worse over time as the carbon track gets bigger and bigger, the
only remedy is to change the coil or electronic ignition module.
White or blue smoke while running may be an indication of an excessively
worn cylinder or rings or a clogged or inoperative breather (the breather
assures that there is always negative pressure in the crankcase - if not,
oil can get forced up into the cylinder). Or, you may be using the fuel
mixture for your 2 stroke weed whacker by mistake!
I'm assuming that you were trying to use the drain plug at the bottom of the
engine, not where the oil is added. Draining is done most effectively when
the plug on the bottom is removed and the mower is placed level again, over a
catch basin and left to sit.
Oil has gotten into the combustion chamber area. The muffler (if it now
contains oil) can be washed (flushed out) in a safe solvent, and allowed to
dry.
When tipping a vertical shaft engine to get to the drain plug, keep the
sparkplug end of the engine higher than the rest of the engine.. and follow
the safety precautions.
Tipping the crankcase end up will put oil at the combustion
chamber end of the engine, and seep into the combustion chamber.. and
sometimes through the crankcase passage into the carburetor area. In cases
where a lot of oil gets into the combustion area.. the engine might not
rotate (due to a hydraulic lock), until the oil has returned to the
crankcase.
If this should happen.. allow the engine to sit for an hour or so, with the
sparkplug end elevated, and most of the oil will return to the crankcase.
If the air/fuel intake area has become flooded with oil, you might need to
have the engine serviced.. the carburetor might need to be removed to
evacuate the oil from that area.
When the oil gets into the combustion area, the sparkplug is usually
soaked.. and after cleaning or replacement, the engine will smoke (for a
short time) like a fog machine. This will often foul the plug again, and
create a lot of carbon in the combustion area. There isn't an effective way
of removing the excess carbon aside from removing the cylinder head.
For an old mower, that might not matter much.. for a new one that you'd
like to get years of trouble-free service from, you might want to consider
having the head removed and the oil & carbon cleaned out.
A combination of the above are also possible. For example, a loose flywheel
could result in it scraping against the magneto yielding a sound like a cat
being squeezed to death (or that of a first year violin student) but possibly
only at high revs :-).
Of course, a badly worn engine can also result in piston and rod slap and
other mechanical noises as internal parts with excessive clearances whack one
another. A complete engine overhaul may be in order or just tolerate it and
plan for a new mower when the final day arrives (or your neighbors take up a
collection).
If the tank is truly leaking, DON'T use the mower and drain the gas - you don't
want to take chances with a possible engine fire or worse.
Obviously, if it is backfiring every other stroke, you have a problem with
the ignition timing, mixture, valves, etc. What this section deals with is
just the normal noise assuming the engine runs properly - and how to reduce
it. Else, you need to perform the proper maintenance first.
Some lawn mowers discharge under the deck. This should reduce the noise
level but the proper (probably spark arresting) muffler must be used or else
you risk igniting dry grass or whatever as you mow!
Note that for a 2 stroke engine, the muffler is particularly critical for
proper operation and substitution may be more difficult.
If you have been following the recommended preventive maintenance procedures,
this may never be needed. But, face it, you do not! The most important PM
that is not likely done by 90 percent of mower owners is to drain the gas
at the end of the season. With float type carburetors in particular, the
result is a buildup which eventually clogs the very fine passageways in
the carburetor. What happens is that the gas in the carburetor bowl
gradually evaporates leaving behind the gunk and varnish. New gas then flows
in from the fuel tank which then evaporates leaving behind more gunk and
varnish, and so on and so on and so on. This eventually, well, gums up the
works by interfering with float movement and clogging the precision metering
holes. Thus, the need for cleaning. Symptoms include difficulty in starting,
flooding, surging, lack of power, difficulty in restarting when hot, etc.
The following procedures are specifically for the common non-adjustable
carburetors used on the vast majority of Craftsman mowers manufactured
in the last 10 years. Carburetors with adjustments and/or a choke are
slightly more complex and may differ in other ways. Refer to a small engine
repair book or your engine manual for further information.
If the bolts are really tight, an open end wrench may be of help but common
sockets may not fit around the bottom bolt. Thin walled sockets may work.
The carburetor can now be moved to the convenience of your workbench.
WARNING: there is still likely a significant amount of gas inside the
float bowl. Initial disassembly at least should be done outside so that
you can dispose of this safely. Working outside is advisable in any case
as the common carburetor cleaning solvents are both flammable and bad for
your health.
IMPORTANT: Before removing any linkages or springs, make detailed diagrams
as to how everything goes together. You will NOT remember this several
hours later!!! Reassembling the linkages EXACTLY as your found them is
critical to the happiness of your engine.
Turn the carburetor upside-down.
Check the throttle plate for free movement - there should be absolutely
no hint of binding or tightness. If there is, then this will need to be
disassembled as well and cleaned:
WARNING: Carburetor cleaner is both flammable and the fumes are toxic. Do
all cleaning away from open flames and outdoors if possible. Wear eye
protection. The stuff will also eat plastics including some plastic eyeglass
lenses.
Take care where non-metallic parts are still in place as extended contact
with harsh solvents may degrade their properties (inlet seat and primer
bulb, if present). Low pressure compressed air may be used to blow out
passages but only use this on the fuel line from inside the carburetor
body - else you may end up with the inlet seat clear across the driveway
never to be found again.
DO NOT use wires or metal instruments to clear any of the passages as their
size is critical.
The small hole in the hollow bolt on the bottom is most critical. Make
sure it is cleaned down to the shiny brass and that this hole is unblocked
and fully open:
If you are absolutely sure there is no hole in the bolt (some models may
forgo this), check further up on the central tube - there may be a tiny
hole about 1/2" from the bottom. There has to be a hole somewhere for the
gas to be sucked up through the carb!
I first use carburetor cleaner inside and out with cotton swabs to remove
all traces of gunk from the inside. Use as many as needed till no more
discoloration shows up. Then, use the broken end of a wooden toothpick or
popsicle stick to clear the .5 mm diameter hole in the side. In severe cases,
this hole may not even be immediately visible due to the varnish and gunk
buildup.
If this hole is narrowed or clogged, the engine may start but then die in a
few seconds. Gas enters the reservoir in the nut slowly or is forced in by
priming but the normal suction cannot replenish it quickly enough.
Fine steel wool may be used on the float hinge pin if it is rough or there
is evidence of rust but do not use anything abrasive on any of the other
parts. Persistence with carburetor cleaner and cloths or paper towels
should prove sufficient.
Inspect the inlet needle and seat. The needle should have sharp uniform
edges and no visible damage to the conical tip. Any damage half way down
the conical part - where it actually contacts the seat - will result in
leakage and flooding. The seat can be removed if damaged by pulling it
out with a hooked wire - careful - you do not want to scratch the body!
If removed, do not reuse but install a replacement. The new seat goes in
groove side first (lubricate with a drop of oil) and can be pressed home
with a blunt rod.
If the throttle plate was disassembled, clean these parts with carburetor
cleaner. Use a cotton swab to get into the bearing surfaces in the carburetor
body.
DO NOT attempt to disassemble the carburetor beyond this point - the pressed
in main fuel nozzle is precisely fitted and is not removable. The welch
plug (pressed in disk) should not be removed unless you suspect contamination
in the primer chamber (if any).
Carburetor rebuild kits are available and are economical where almost any
parts need replacement.
(From: Jim Williamson (Willjim@gte.net).)
If soaking the carburetor in cleaner:
When you remove each part from the dip tank rinse it with warm/hot water (as
hot as your hands can reasonably stand). The parts that have passages - force
water through the passage. This does two things: (1) rinses the internal
passage of the cleaner and any old junk (2) gives you a VISUAL check that
water is coming out the other end of the passage. The visual check is the key
here - you could use compressed air to rinse the passages but you don't see
the exit stream. On a clean passage the exit stream will be nice and solid
indicating no particles hanging up in the passage.
Now as for the hot water - this is to help dry the parts off - evaporation.
Sometimes once I've rinsed the parts off I'll use compressed air to further
dry the passages - or at least manually blowing through them.
If the primer bulb is on the carburetor, there is a 'welch
plug' (a metal disk pressed into a mating cavity) sealing the primer
chamber. On the side toward the center, there is a tiny rectangular hole
that must be open - it often gets clogged and may not even be readily
apparent. Do not attempt to remove the welch plug unless you seriously
suspect something is inside. If pressing the primer bulb results in a
blast of air out of the hole, it's probably fine. Where the primer is
separate from the carburetor, there is usually no welch plug.
Note: When tightening the float bowel, take care that the O-ring doesn't
get pinched or kinked resulting in an inadequate seal or no seal. A
narrow stick may be useful to help it along. If the carburetor hasn't
been removed from the engine, a mirror will be needed to inspect it.
If you removed the throttle assembly:
Confirm that the throttle plate moves freely between a fully closed and
fully open position - there should be no hint of binding or stiffness.
Now for the main event:
You can test for proper operation using low pressure compressed air (i.e.,
by blowing into the fuel hose), or water or gas. Water is safest but
you must make sure to dry everything thoroughly before final assembly.
To do this, temporarily reassemble the bowl with the hex head bolt. With
the carburetor upright, dribble water into the fuel hose until it accepts
no more - perhaps an ounce or two. There should be no leakage - the level
of water in the hose should not change at all once it stops. If there is
any leakage, there is still a problem with the inlet needle or seat - or
the float is gas-logged.
The user speed control (if any) pulls on a spring which is attached to the
2nd hole from the top on the governor lever. For engines with no speed
control, there is a fixed plate or tang to which the spring is attached.
Some amount of adjustment is possible by bending this plate.
The carburetor throttle plate has several holes in it. The one that is
probably used is that closest to the little cutout (which I can't show with
ASCII art) and the tip of the throttle plate return spring. You can probably
confirm this by looking for which hole has the paint worn off!
See: Neil's Tecumseh
Throttle and Carburetor Linkage Page for some slightly better diagrams. :)
Inspect around the fuel hose and carburetor body for fuel leaks. If
gas starts dripping from the air inlet or anywhere else, there is still
a problem with the inlet needle and seat. Disassembly will be required.
Only a few seconds are needed for the gas to fill the carburetor bowl.
Assuming there are no leaks, install the air filter and reattach the
spark plug wire or reinstall the spark plug. Attempt the normal starting
procedure - prime if recommended.
The engine should start on the first pull! Immediately move the throttle
selector to LOW if you have this option. Confirm immediately that it
stabilizes at a reasonable speed - stop it quickly if it sounds like the
mower is preparing for takeoff - your governor connections are incorrect
or binding. If it runs at a fast speed with the speed selector set at
LOW, the governor spring is probably in the wrong hole. Check it.
Listen and feel for any significant unevenness, surging, or other unusual
behavior. Stop the mower, wait a few seconds, and restart. It should
restart with a single pull without priming.
Mow for a few minutes. Stop the engine and confirm that it restarts without
priming. Listen and feel for any indication of lack of power or other
unusual behavior.
Go take a dinner break. Then confirm that the engine will now start - priming
may be needed since it will now be cold.
First, test for spark. If there is a spark, try replacing the spark plug
since this is the most likely cause of ignition problems. With a spark
present, there could still be ignition system problems but this is much
less likely.
You may be able to test the points to some extent if you can get to the wire
that connects to the magneto or the STOP switch. A multimeter on the low
ohms scale will the permit you to watch the opening and closing of the points.
If this confirms that the points are operating the condenser could still
be defective, the breaker arm could be sluggish, or the point gap could
be grossly out of adjustment.
To proceed further:
If any of these problems are present, replace the points and condenser as
well - a bad condenser may be the cause of the points failure it is not
really possible to fully test it.
You can also test for electrical operation of the points using a multimeter
on the low ohms scale while rotating the crankshaft (you will have to use
the blade - careful) or operating the breaker arm manually.
Or better yet, just replace the points and condenser. The cost is minimal
(probably under $5 for a rebuild kit) and you have already done most of
the work.
While measuring piston position with a scale through the spark plug hole,
rotate the crankshaft until the piston is precisely at TDC and note this
distance. (There are special timing gauges for this purpose with lock
screws to hold the setting but a little ruler will work just fine.)
Now, turn the crankshaft in the opposite direction from normal rotation
(usually counterclockwise as viewed from the flywheel end) until the
piston moves down .25 inches or so and then turn it slowly in the normal
direction of rotation until the piston position is precisely at the timing
dimension listed in your engine specifications.
The flywheel should be temporarily re-installed without tightening the nut.
Rotate the crankshaft until the timing marks are precisely aligned.
Carefully remove the flywheel without disturbing the crankshaft position.
The cause of a broken cord is obvious. The cause for a failure to retract
could be a broken spring, tangled or frayed rope, or some other mechanical
failure. A broken spring will require total disassembly of the starter
mechanism - fortunately there really isn't that much involved.
With some designs, it is possible to replace the cord without fully
disassembling the starter mechanism - by threading the cord in and
tying a not in the end - but after rotating it several turns to put
the proper tension on the spring. This is relatively safe but may
be frustrating as 3 hands are sometimes needed.
Where safe disassembly is not obvious, I would recommend that you refer
to a book on lawn mower or small engine repair from the library or the
service manual for the mower, if possible. You may be able to find specific
step-by-step instructions which will minimize your risk of injury from
an encounter with an uncontrolled spring.
WARNING: Take extreme care should you need to disassemble the portion of the
starter that includes the mainspring - that can be nasty.
The idle mixture screw is the one with the step.
I assume you have any choke off, throttle connected properly with spring
return, etc.
What happens if you close both idle and main jets? Does it starve?
I would expect that you should be able to stop fuel flow totally. If
this is not possible, your needles or something else is incorrect/worn
or fuel is somehow bypassing the jets which is also wrong.
Did you compare the old and new parts to make sure they gave you the
correct kit?
It also recommend removing the Welch plug and blowing compressed air through
the passages to clean.
It might also be a problem in the diaphragm spring pressure but without
seeing it, no way of knowing. The diaphragm acts against atmospheric
pressure. There is a spring on the inlet needle which if missing would
run very rich. Chilten has a detailed diagram - really no way of knowing
if your assembly was done correctly. Also, warns again using harsh
cleaners on non-metallic parts and clearing all vent holes.
However, I rather suspect that comment about running rich is not correct
as an engine running very rich would lack power if it continued to run
at all. Your throttle may be stuck wide open and it may be over revving.
Your public library should have some Chilten or other books like those listed
in the section: References. These should include
diagrams of the diaphragm type carburetor.
(From: Greg Fretwell (JRFC31A@prodigy.com).)
The best way is to braze it, but before you get your torch out take a bottle
of ammonia to the car wash and have them steam the tank out, pour in some
ammonia and rinse. Repeat a few times. Ammonia will remove the residual
gasoline and make it safe to weld on. This is the procedure required by the
welding shop that fixed my tank. They needed to see the receipt from the car
wash before I could even bring the tank on the property.
(From: Doug Younker (dougy@ruraltel.net).)
I have gotten lucky and have been able to solder repair leaks in small engine
tanks using my 140 watt soldering gun after leaving the tank to preheat in the
sun all afternoon while I was at work. You have to be patient to do so...
(From: Jeremy (js5301@gmail.com).)
If you want to work on a metal gas tank, empty the gas and put some dry ice
in the tank. The dry ice will vaporize, filling the gas tank with carbon
dioxide thus removing oxygen and gasoline vapors.
For detailed instructions on valve grinding, cylinder reboring, or main
bearing reaming, for example, you should refer to one or more of the
books listed in the section: References. However,
this chapter will give you the general feel and basic information needed to
perform many common types of simple overhaul operations and to evaluate the
need for more drastic action - such as a trip to the new lawn mower store!
Depending on your particular problem(s), only a subset of these sections
may apply. For example, inspection and cleaning of the valves and
combustion chamber - even valve regrinding (but we said we weren't going
to talk about that!) can be done with a minimum of engine disassembly.
The following are indications that at least a partial overhaul may be needed:
In some cases, multiple problems may be present and/or there may just be
excessive wear of parts like the cylinder, rings, and piston. Under these
circumstances, the cylinder may need to be rebored to accept a replacement
oversize piston and ring set. The cost of the parts and labor (you really
don't want to rebore a cylinder) will likely be more than you want to spend.
This is when a new engine or mower is the best option.
(From: Mother (jmg14213@earthlink.net).)
As a finalist in the All-American Engine Repair Championships formerly held at
the Outdoor Power Equipment EXPO (an industry trade show) in the Tecumseh
division, and as a Briggs and Stratton Master Service Technician, it has been
my experience that:
If this engine is on a top of the line product, such as Ariens, Snapper, or
BearCat, it is probably worth repairing, as a new comparable product is big
bucks (and overpriced).
If this engine is on a mid-range product, such as Toro, Simplicity, John
Deere, Husqvarna (European product, not USA built), etc., then repair is
probably still a good option, due to the overpricing of similar replacement
products.
If it is on a Murray, Noma, AMF, Dynamark, Ultra, Sears, MTD, YardMan, White,
Husqvarna (USA built by Murray/Noma), or other discount store brand, go buy a
new machine. The cost of a new unit is not much more than the cost of the
engine repairs, and then you won't have a worn out piece of discount store
equipment to break down again in three weeks when something else goes bad...
Note that this procedure may always yield a very low reading if there is
a compression release mechanism on your engine - which is very likely. In
this case, the crankshaft must be spun in the opposite from normal direction
by the flywheel (counterclockwise when viewed from the flywheel end, with the
starter removed).
For Briggs & Stratton engines, the manufacturer simply recommends spinning
the crankshaft by the flywheel in the opposite from the normal direction with
the normal spark plug installed. A sharp rebound (as it compresses the
trapped air since the compression release mechanism is not active in reverse)
indicates good compression. Little or no rebound indicates low compression
and need for service.
If you are not the detail oriented meticulous type, you may be better off
leaving this sort of overhaul to a professional or buying a new engine or
mower. Most parts must go back in exactly the same orientation as they were
originally - including matching of timing marks on the crankshaft and cam
gears. Even the piston is not symmetrical - though this is not obvious except
by taking detailed measurements. Nonetheless, it will not work well if at
all, or will wear quickly if rotated 180 degrees upon reassembly.
Furthermore, once a wear pattern has developed, it is generally a good idea
to replace parts in exactly the same position - the direction of the piston
(wrist) pin or location of the intake and exhaust valve lifters. Violating
this rule won't result in immediate failure but could lead to excessive wear
and reduced life
What this means is that you cannot assume anything about the parts you
remove. Even if they look identical at first glance, they may have a
definite right and wrong orientation and/or may want to be replaced in
exactly the same location. Even lowly head bolts may be of different
lengths. Make notes and diagrams. Most of these will be pretty simple
but they will save your hide in the end!
Bearing surfaces are very finely ground and polished - just dinging the
crank pin journal surface against a steel part will put a nick in the
relatively soft bearing which will need to be carefully removed as best
you can - affecting as little else as possible - with very fine emery cloth.
In addition, if you don't like to get your hands dirty and oily, forget it.
You will have disgusting black crud under any surviving fingernails for
days. This is a messy operation! The outside of the engine will be coated
with decayed grass clippings, dust, and dirt. The inside of the crankcase
will have the remnants of old used motor oil (also a carcinogen) and the
combustion chamber will be coated with filthy carbon deposits.
At the same time, cleanliness is critical when reassembling as any particles
of dirt or metal will find their way between rotating parts resulting in
excessive wear or worse.
Having said all that, overhauling a small engine is not like overhauling an
automobile engine. In the words of a colleague: "It's just a frick'n
lawn mower". What this means is that you can get away with tolerances,
imperfections, and mistakes in dealing with a small engine that would
be unacceptable for the health of your Chevy or Porsch.
You place one in between the rod bearing and crank pin journal and tighten
to specifications. When removed, simple measurements on the markings on the
squashed plastigauge will very precisely determine the clearance, taper,
and out-of-round specifications for your bearing. It is also possible to
obtain most of this information by using slips of paper or foil of known
thickness but this will not be as accurate or convenient.
Fortunately, the metal ridge is rarely a problem on lawn mower engines and
the carbon ridge can be removed with a simple homemade tool which is just
a soft metal (i.e., aluminum or brass) piece with a straight edge or inside
right angle. You probably will not need an expensive commercial ridge
reamer tool. You will not need one at all unless you will be removing
the piston.
Lay out a healthy layer of old newspapers to protect the workbench from
oil and solvent drips and damage from heavy tools and parts.
Mechanically, 2 stroke engines are very similar. In many respects, they
are simpler having no camshaft operated valves or oil pump. There is no
oil to drain or change. However, needle bearings are used in key spots
which complicate matters slightly. Refer to one of the books listed in
the section: References for detailed 2 stroke overhaul
procedures.
If the bolts are really tight, an open end wrench may be of help but common
sockets may not fit around the bottom bolt. Thin walled sockets may work.
The carburetor can now be set aside or disassembled and cleaned. (See the
section: Cleaning Craftsman (Tecumseh) carburetors.
WARNING: there is still likely a significant amount of gas inside the
float bowl. If turned on its side or upside-down, this gas will come
gushing out. Therefore, it is best to set the carburetor aside in an
outdoor area in an upright position. Plug the intake manifold and fuel
pipe with wadded up paper towels or rags to prevent the entry of dirt.
Some mufflers simply screw into the cylinder using pipe threads. Others
are mounted with a couple of bolts.
(From: Brian (Aquakidd13@aol.com).)
On old 3.5 and 4 HP Briggs and stratton engines the cam acts weirdly and
opens the exhaust valve slightly on the compression stroke thus loosing air
and fuel mixture and compression. This is probably due to wear of the
valve or valve seat resulting in the cam pushing the valve up when it's
really not supposed to be touching the tappet.
You need to pull the head off and crank
it slowly and watch the exhaust valve, if both valves close and then the
exhaust valve pops up, an adjustment is required. To fix this grind the
exhaust valve tappet side down 0.5 MM put the valve back in and check it out
if it still does grind a little more off. the engine will run smoother
than before and a little better
(From: Sam.)
Note that many small Briggs and Stratton (and other) engines include a
compression release feature to make starting easier. This has a similar
effect in that it opens the exhaust valve during part of the compression
stroke reducing the effort needed to pull the starter rope. This should
not be confused with what Brian is describing, above.
At normal operating rpm, the governor moves a secondary piece on the
exhaust valve cam out of the way so that the behavior returns to normal.
Unfortunately, unless the crankcase is open, there is no easy way to
determine whether the compression release is present on your engine
without a service manual.
Note: the small gear on the crankshaft may be a press-fit and may not be
considered serviceable by itself without replacing the entire crankshaft.
However, I have been able to remove it non-destructively by gently tapping
on each side using a soft metal bar (e.g., brass) and a small hammer.
(When I had to do this, the guy at the engine parts store was surprised
that I was able to get it off without damage.) Heating the replacement
gear will expand it and reduce the force needed to press-fit it onto the
crankshaft. Similar gentle tapping will then work once the gear is aligned
with the indexing pin.
Determining this requires a visual inspection and taking measurements of
all critical dimensions of bearings, cylinder, piston, and rings. Some of
the inspection is subjective - how badly scored a bearing surface is before
it must be replaced or reground. A few score marks around the circumference
of a bearing surface will not adversely affect operation or wear. How few
is a few? Perhaps if less than 10% or so of the surface is affected. You
are not going to spend as much to repair the mower as it cost in the first
place in any case so don't lose sleep over it.
Measurements may come up marginal as well. For example, if the limit listed
in your engine specifications is .0015" and you measure .002" will this be a
serious problem requiring the replacement of expensive parts? Probably not.
You may get less than optimal life out of the engine but it will probably
still work fairly well and for a long time. So many other factors can affect
life that this may have no effect at all.
The following items should be visually inspected. If any significant wear
is indicated, precise measurements should be made:
Follow the instructions that came with the plastigauge to take measurements.
Consult your engine specifications for acceptable limits. Use judgement
in determining whether slight out-of-spec measurements will necessitate
replacement or major rebuild.
If you had a rod failure due to lack of oil (remember what we said about
the importance of oil - see the section: Rod disasters -
or why the oil and governor are kind of important) - then there could be
a variety of types of damage that will make these measurements academic. The
rod my have broken in half or the cap may have literally exploded into
multiple pieces. In many cases, the crank pin journal will escape relatively
unscathed but needless to say, you will need a new rod and cap - not cheap!
If any filing, sanding, or grinding was involved, make sure all traces of
abrasives have been removed from every part. The best approach is to clean
with soap and water or mild detergent and dry thoroughly. Then immediately
coat all ferrous parts with engine oil to prevent rust.
Where the internal moving parts are involved, liberal use of fresh engine
oil will also make things to go together smoothly and help protect the
surfaces from damage due to initial lack of lubrication.
Note the typical arrangement (from top to bottom):
But, you drew a diagram, right?
Note: if new rings are installed, you should deglaze the cylinder
wall with fine emery cloth in a cross-hatch pattern (diagonal strokes).
This is needed break in the new rings. Then very thoroughly clean the
cylinder to remove all traces of abrasive residue.
For the following, position the crankcase flywheel/magneto side down on
some wooden blocks so that when the crankshaft is installed, it's end will
be clear of the table-top.
CAUTION: Do not use a metal hammer - there is a good chance you will crack
the fragile aluminum piston.
CAUTION: Don't let the bottom of the rod or rod bolts hit the crankshaft!
Put a wad of rag inside to prevent this.
CAUTION: double check that you have the match marks aligned. If correct,
the bearing formed by the rod end and cap will fit the crank pin journal
perfectly - seated fully - with no free play even when only finger tight.
If you attempt to fully tighten the rod nuts or bolts and the cap is
backwards, you may ruin the rod and cap by distorting the soft metal.
Now, use a torque wrench to tighten the nuts or bolts to the proper torque
as listed in your engine manual. Alternate between the two nuts or bolts
tightening in small equal increments until the proper torque is reached.
Where a range is specified, aim for the middle.
Where a lock plate is involved, torque to the middle of the acceptable range
and then tighten the nuts or bolts just enough further to align a flat with
the edge of the plate. Then, bend the plate over to lock it in place. DO
NOT reuse an old lock plate.
It may be a tight fit to get a torque wrench inside the crankcase. Here are
a couple of comments:
It is just possible to get both the clearance and angle to use the torque
wrench effectively. With a ratcheting torque wrench it would be easier but
this is not essential.
THIS ASSEMBLY IS MOST CRITICAL and is probably the single most important
place to get the torque just right. Too tight and (especially for aluminum
alloy rods/caps) you will strip the threads and/or distort the precision
fit. Too loose and the bolts will eventually work their way out. You
really don't want the cap to pop off while the engine is running at full
power!
Engine repair manuals always recommend using a new head gasket. The old
one has shaped itself to the texture and imperfections of the head and
cylinder and you could never match this up perfectly upon reassembly. The
result can be leakage of hot combustion gases and ultimate failure of the
gasket and possible damage to the mating surfaces.
However, if you have not done anything to the head or cylinder surfaces and
the gasket is in essentially perfect condition, you can risk reusing it but
I won't guarantee long term reliability! My general recommendation is that
you use a new head gasket once you are sure that everything works properly
and thus there will be no need to remove the head again. Unless the old one
is damaged, it will work fine for testing purposes.
A typical Tecumseh bolt tightening sequence is shown below (except 8 HP).
Check your service manual for the specific recommended procedure for your
particular model engine.
Assuming nothing appears wrong, run it for a while at slow speed (if you
have the option). Continue to be on the lookout for anything unusual.
After a few minutes, stop it.
Let is sit for 10 minutes or so and then check, and if necessary, top off
the oil.
Now, restart and run it at high. Mow a few lawns.
Congratulations! Hopefully, your engine will now serve you for many more
years - or until the blade hits the next curb!
Here is how to fill a gas can to minimize the danger of fire:
More information can be found on:
Chevron's Technical and
Safety Publications Page.
There are various safeguards to protect the mower from damage should a blade
tip hit something but these don't always work. Why?
There is protection for the upper and lower parts of the crankshaft after all:
In many cases, both of these will break free at the same time.
However, if the shock is severe enough, much more serious damage can result.
Here is why: When one end of the blade hits a curb, for example, the inertia
of the mass of the blade alone (rotating at high speed) will attempt to push
the shaft sideways. This is pretty much independent of the rest of the
engine.
In the diagram below, the blade is rotating clockwise. When the left-hand
tip hits the curb, the right-hand side due to the inertia of the entire
right-hand half of the blade wants to continue to move (down in this diagram)
with the 'X' as the fulcrum. The entire left-hand half section of the blade
contributes relatively little. This results in a net significant sideways
(downward in the diagram) bending force on the crankshaft. The unavoidable
arrangement of the fulcrum at one end and the shaft in the middle makes the
situation even worse as the force resulting from the blade tip (the right hand
one in this example) is amplified by the up to 2:1 mechanical advantage of the
lever arm (the tip is twice as far from X and the shaft).
While the rotating mass of the engine is attempting to shear the blade lock
key, the inertia of the blade is trying to push the crankshaft sideways.
The net result could be a severely bent crankshaft - a very expensive
repair. An 8 to 10 degree bend is not unusual for a typical Craftsman-class
mower running at full power. Any detectable bend in the crankshaft requires
replacement - it is not safe to attempt to straighten it. A bend resulting
in the blade tips wobbling by more than a fraction of an inch, there will be
unacceptable and dangerous vibration when the mower is run. In addition, the
original trauma (as well as attempting to run with a bent crankshaft) can
damage other parts like the main bearings and connecting rod. The blade lock
and flywheel keys will likely be broken as well but these are insignificant
in comparison to the cost of major replacement parts and the labor involved
in their installation.
The time and effort needed to disassemble the engine is significant and the
crankshaft is probably the single most expensive part of the engine. In
fact, purchasing a new crankshaft may be more expensive than an entire new
lawn mower! It is quite possible that unless you have access to low cost
replacement parts from a salvage yard and have the free time to do the work,
repair may not make sense.
Therefore, don't let this happen to you. Your curbs and rocks don't grow
that quickly and do not generally require mowing!
Apparently, some mowers are made with swing tip blades:
(From: Roderick Carmichael (carmic@nex.net.au).)
Why are these not common in America? Conspiracy to sell replacement parts
by the small engine manufacturers? :-). You would have to really work at
bashing a curb to bend a crankshaft with such a mower.
Another possible approach - applicable for both new lawn mower designs as well
as field upgrades - would be to replace the heavy steel blade with one made
of nylon with a molded-in steel edge. An auxiliary flywheel might have to
be added (under the deck) to provide the needed inertia (normally supplied
by the steel blade) for the engine to start and run properly and to help the
mower plow through tall grass. However, since this additional flywheel could
never be stopped abruptly due to hitting a rock or curb, its inertia would
never contribute to a sideways bending force on the crankshaft. The greatly
reduced mass and increased flexibility of a reinforced nylon blade should
virtually eliminate the possibility of a bent crankshaft from such unfortunate
incidents. See the section: Why you really don't want to
attempt to move an immovable object.
(From: Mowerman (mowerman2687@my-dejanews.com).)
I have been reconditioning lawn mowers for many years and find it
fascinating what design goes into some of this equipment. Like arrangements to
prevent the crankshaft from bending if the blade hits something. Most engines
have an aluminum key at the flywheel but this will not stop shaft bending
most of the time. Mower manufacturer uses many methods. Lawn boy has a tapered
shaft at blade level and so the shaft has no key and the blade slips if
hit. Some other mowers had steel washers and fiber washers nearest the blade
like a clutch I seen this on some antique mowers. The best idea is disc with
small flail blades or short blade with flail at end. Manufacturers in New
Zealand and Australia use this method on their domestic mower mostly and it
works well. Victa of Australia was one of the first ones around here with this
idea. I am sure you have them over there to no doubt. I hope this information
will be to some help.
I recently came across a description of a blade assembly similar to the one
suggested by you to make bending the crankshaft difficult. This is in the
Royal Horticultural Societies' "Encyclopedia of Gardening". In the tools
and accessories section, under the "lawn mowers" subsection, a caption says:
"Plastic disk. This cheap replacement part cuts the grass by rotating
horizontally". The inset shows rotary, cylinder, and "Flymo" mowers. A
picture of the part shows a disc almost the diameter of a regular blade,
with one blade joined to the circumference by a pin so that centrifugal
force keeps it radial. This blade is short and narrow compared to the
plastic disc; no telling if it is plastic or metal. There is no further
reference to this part in the text. In my translation, it is on page 465.
If only they had included a name or supplier!
I have recently purchased a new rotary lawn mower and appear to have started
wrecking it in the first two weeks of use! Problem is, my property has lawns
that run alongside a gravel driveway, and its often very hard to guarantee
there are no stones lying in the grass before you start mowing. Not
surprisingly I often hit small stones. These usually cause no harm, but today
some teenagers were mowing my lawns and hit a real monster that measured
approximately three inches by two by one, and weighed more than half a pound!
Although the mower seems still to work OK, the impact has created a three inch
long tear in the mower's cast aluminum body. Not a nice thing to have happen
to a new machine!
Despite the stone's size, I was surprised at the size of the resulting tear in
mower's more than 1/4 inch thick aluminum casing. I hadn't imagined a rotary
mower blade powered by a 5 HP Briggs and Stratton motor could produce such
force!
It would be interesting to hear from others who have survived similar
experiences and to get an idea from any budding engineers on whether its
perfectly reasonable for a stone this size to do such damage to the body of my
mower - or whether it's more likely the body casting had a manufacturing
defect that made it split prematurely?
The primary cause was likely a lack of oil - I should have checked it before
attempting to run the engine for more than a few seconds. I have no idea
whether someone had actually drained the oil for who knows what reason or
it was just very low. In addition, I may have accidentally put the governor
link back in the wrong hole permitting the engine to run at an abnormally
high (and dangerous) speed.
There was no warning. The rod cap just exploded into e pieces (and this was
at normal speed) and took a nice chunk out of the interior of the crankcase.
Based on a post mortem of the rod, it appears as though one of the cap screws
just loosened and backed its way out totally - there was no evidence of
thread damage that would be expected if it were ripped out - and fell into
the sump. With only one screw holding the rod and cap together, eventual
failure was inevitable. Due to the offset design of the cap, this probably
worked for a while since most of the force is on the rod.
Discoloration indicated excessive heating but no obvious bearing damage was
evident that could be attributed to the lack-of-oil condition. The bearing
was not in pristine condition but the type of scoring seemed to be more due
to just poor general maintenance - lack of regular oil changes - than to this
incident in particular.
Lessons: Check the oil level no matter what if there is any question or you
are working on an engine of unknown history. Double check the governor
linkages - take notes during disassembly - and be aware of what a normal
speed sounds like for your type of engine (2 stroke or 4 stroke). If in
doubt, install the link in the hole that would result in lower RPMs - closer
to the carburetor. You can always move it later.
(From: David Thomas (dthomas@NO.cityutil.com).)
The following assumes it is (was) a small push mower with a vertical shaft
engine and that you drained the oil the preceding fall.
What little oil that was left in the bushing areas on the crank have burned
down to tar. The piston may or may not be seized. Either way you'll need to
break the engine down (pulling the flywheel is the hardest thing about it)
and clean the tar out.
If this is beyond your abilities, try spraying penetrating oil on the crank
around the bushing areas both on top (may still have to remove the flywheel to
get to this area) and bottom as well as around the piston as the other
gentleman suggested. (If you can't remove the head, pull the spark plug and
spray penetrating oil or WD40 inside the chamber using one of those straw
things that comes with the can so that you can direct the spray around all the
walls of the cylinder, put the plug back in so it doesn't all evaporate and
then set the engine so the piston is pointed straight up and let it soak a few
hours.)
Last choice is to fill the crankcase with about a pint or two of penetrating
oil (and spray inside the combustion chamber as stated above) then slosh it
around the engine, turning the engine every which way and upside down, let it
soak for a couple of hours repeating the sloshing every so often and changing
the position of the engine so that you alternate soaking each bushing area and
the bottom of the piston and then try the pull rope again. Be *sure* to
disable the spark 'cause you *sure* don't want it to start with that light
oil in the crankcase.
If it does free up, drain out the light oil and add the normal recommended
oil before trying to start it. If it starts (it will smoke like the devil
while it burns that light oil), let it run at idle speed until it warms up
then shut it down and change the oil. It may still burn oil and smoke since
the piston walls are probably scored badly so check the oil every time before
starting it even after a short break until you get a feel for how much its
going to burn.
(I had one engine that I did this with that used all most as much oil as it
did gas. I had to clean the crud out of the spark plug before each mowing.)
(From: Brian Fistler (brian_34_@yahoo.com).)
If it's a Tecumseh engine, throw it away... Even if you get it running,
it'll probably throw a rod soon (not like it wouldn't even if you hadn't
seized it... :-)
If it's a Briggs, try putting oil in it first, then remove the spark
plug and spray a liberal amount of WD 40 in there... You might have to
let it set for a day or so, then, LEAVING THE SPARK PLUG OUT try turning
the engine using the blade... Once you get it freed up, most likely it's
run fine and probably last a few more years...
When I was a kid, my best friend and myself used to "work" on Briggs
engines, we'd tear them down, fix broken ones from the junk yard, and
most fun of all was "torturing" one... After seizing it up by finding
out what would, and would not keep the thing running by spraying it in
the carburetor (i.e., using hair spray, WD-40, paint thinner, etc...) We
finally found that a certain spray engine degreaser of the era *would*
run the engine, it would not run it for *long* because it removed the
oil from the cylinder walls, and the engine would seize up...
That gave us an excuse to tear the engine down and find out how to get it
going again... After the 3rd or 4th time seizing the engine with
various products, we just decided to cut a hole in the side of the block
and put a piece of Plexiglass there, so we could get easier access...
We ran that poor engine with every possible thing in the crank case,
including pure water... (Side note: Water didn't seize the engine, as
long as you didn't allow all of it to evaporate)
When the engine would seize up, all we ever had to do was put oil back
in the case, spray a little WD-40 in the spark plug, and hit the blade a
few times with a hammer to get it starting to turn...
That motor kept us entertained for an entire summer... :-)
Possibly, just letting it sit for awhile (in the normal position!) will
allow the oil to drain back into the crankcase sump.
If oil is really trapped between the piston and the head, then you may be
able to just tip the lawn mower so that the spark plug hole is down (a buddy
may come in handy) and drain the oil out through there.
Alternatively, you should be able to suck most of it out with a kitchen
baster and narrow extension tube (make sure it is made of something that
won't scratch the interior of the cylinder and the piston) through the spark
plug hole.
You don't have to get every last drop. What is left should not prevent you
from starting the engine - it will just belch gobs of white/blue smoke for a
few seconds after it kicks over as the remaining oil burns off. Keep in
mind that squirting a half an ounce or so of engine oil into the cylinder is
recommended when winterizing to protect the cylinder from rust so it should
not be a problem.
In fact, I would expect that pulling the starter a few times will clear
most of it in any case. It is possible that you have other problems -
hopefully you didn't turn it over carburetor side down!. (In this case,
the air filter may need to be removed and cleaned or replaced.) It may
even be that your initial attempts to start it with an oil in the cylinder
have resulted in a flooded the engine (excess gas) and waiting will clear
that as well.
Some of the following information may be model specific but most applies
to any engine that has gotten oil in the cylinder and/or carburetor due to
tipping:
(From: J. Matthew Good (jmg14213@ix.netcom.com).)
First, my guess is that it is a Briggs QUANTUM or SIGNATURE SERIES engine,
with the paper air filter. Go buy a new filter, as that one full of oil is
shot.
Next, remove the plug and secure the plug wire away from the opening. Crank
the engine a few times to clear the liquids out of the cylinder. Reinstall
the plug. Now take a 1/2 inch box wrench and loosen (don't remove) the
plug/nut on the bottom of the carburetor until gas flows clear through it, and
retighten it. This should get the oil out of the carburetor. Now, check the
oil.
Since you lost so much into the carb, and air filter, and it only holds 2 and
1/2 cups total you will probably need to add oil. If not, you may have gas in
the oil as well. Drain the oil into a pan for recycling by tipping the mower
air filter up, and dipstick tube down. Fill with clean SAE 30 HD oil. DO NOT
use 5W30, 10W30, 10W40, or any other W oil. Just SAE 30 HD from any discount
store will be fine. Do NOT use SAE 30 ND, it does not have the needed
detergents.
Now you have the liquid out of the cylinder, the oil out of the carb, the gas
out of the oil, the air filter OFF, and you are ready to start the engine. If
it has a CHOKE, set it for full choke, if a primer, press it 3 times. Pull
the rope until it starts. Let it JUST RUN until the smoke clears, don't mow or
anything else until the smoke clears and you reinstall the NEW air filter.
The reason I guessed it was a Quantum is that this is the only engine I know
of that automatically puts oil in the air filter if you tip it for sharpening.
That's why the first thing I do to any Quantum that comes in for service is
remove the air filter and put it in a safe place.
(From: Lloyd E. Sponenburgh (lloyds@fiscalinfo.com).)
Actually, a judicious tilt *away* from the carb will coat the underskirts
of the cylinder and piston with oil so as to make starting *easier*. This
improves compression. It's an old salesman's trick to show just how easy
it is to start the engine.
For the slinger to operate, it must dip into the oil! At too steep an
angle, the slinger may be whipping up fumes and no oil!
At too steep an angle, the intake of the oil pump may be exposed sucking
fumes instead of oil!
With the oil filled to the correct level (yet another reason to check the oil
every time you mow!), the oil starvation angle should be greater than anything
you are likely to safely encounter unless you have a very hilly lawn.
However, if you do mow steep slopes for more than a few seconds (e.g., to turn
around), it would be worth determining if this could be a problem for your
engine.
Two stroke engines do not have this problem since the oil is mixed with the
gasoline. As long as the fuel feed is working, the engine should be happy and
the mower will mow! However, I do not like 2 stroke engines because of their
generally higher production of smoke and pollution.
(From: Walt Conner (jerrbear@midwest.net).)
Oil starvation can happen. If you must mow on a very steep slope, look to
see which side the valve cover plate is on. This side of the engine will
also have a semi-circular bulge in the crankcase while the opposite side
will be pretty well flat. The side with the bulge will have the oil
slinger located below the bulge. Keeping this side down slope should keep
you in oil anywhere you can stand.
When failure occurs, usually the connecting rod is first to go, sometimes the
top main bearing seizes. Either occurrence usually means it's time for a new
mower.
For really hilly mowing, you may want to consider a model that uses a 2 stroke
engine such as Lawn Boy.
(From: Dwayne (Dwayne@mddc.com).)
There is some argument that draining all the fuel from the system is bad,
allowing the carb to dry out and the inside of the fuel tank to rust. That
was the case on my motorcycle; the guy who had it always drained the fuel
for storage and it ruined the tank. I always just add fuel stabilizer to
the tank, fill it completely, and run it for a short time and have never
had problems.
(From: Matt Howell (howell@ll.mit.edu).)
Fuel stabilizer's purpose is to prevent souring, and hence, the need to drain
the fuel system before storage. In my experience, my equipment starts right
up each season with stabilizer in the fuel. I would suggest you clean/rebuild
the carburetor. Repair kits are cheap, and easy. Good luck!
(Editor's comments).
I have cleaned and rebuilt too many Tecumseh carburetors (mostly from neglected
Craftsman lawn mowers). The cause in most of these was almost certainly
gasoline left in the fuel tank between mowing seasons. You might get away
with it for a couple of years but eventually the goop will prevail. I would
definitely recommend draining the gas with these. The fuel tanks are plastic
in any case and there are only a few steel parts in the carburetor and rusting
of these is not that likely. A fuel stabilizer may not prevent the buildup of
gunk and varnish as a result of the slow but inevitable process of fuel
evaporation in the carburetor and replenishment from the fuel tank.
For other types, I would still recommend draining the fuel tank and running
the engine until the carburetor is dry. I believe that this will result in
the best long term reliability in most cases. Now, if you live in a swamp
and mow the seaweed.... :-)
If the owner claims the mower will start and is prepared to demonstrate, this
is usually a good sign! However, first, take a moment to check the following:
(Disconnect the spark plug wire, and tie it safely away from the spark plug
terminal to prevent accidental starting if you are doing anything more than
looking.)
CAUTION: the oil will be hot if you check it after the engine has been
running for more than a couple of minutes.
If there is gasoline in the fuel tank and it will start without undo effort,
then there is an excellent chance that the engine is in good condition.
In most cases, if the engine starts reasonably easily, there will be no really
serious problems. The ignition system may require a tune-up or the carburetor
may need cleaning and/or adjustment. Even a hard-to-start mower may very
likely restored to tip-top shape with this type of intermediate level
maintenance. Of course, the blade may have to be sharpened or replaced.
If the engine doesn't work - no gas in the fuel tank and no handy gas can
is usually a tip off of this - how can you be fairly sure that there are
no major mechanical problems? Note that the objective here is not to
identify **the** problem but to have a good idea of whether repairs will
be really expensive or difficult. Thus, we won't even bother checking the
carburetor or spark as problems in these areas are minor compared to those
caused by internal mechanical damage. Here are some simple tests you can
do without tools and without overly upsetting the people running the sale
or junk yard:
WARNING: disconnect the spark plug wire and tie it safely away from the
spark plug terminal if you will be doing anything under the deck. Yes,
I know, there is nothing in the fuel tank but it doesn't hurt to be safe.
Use a rag or proper work gloves if you attempt to rotate the blade directly.
I picked a mower off the curb once where the cord was broken due to guess
what - a clump of grass stuck between the blade and deck. Apparently, the
cord was quite worn and the mower stalled on the clump of grass. The next
yank likely resulted in a stream of 4 letter expletives and the mower was
put out in the trash. Extracting the grass clump and replacing the cord
yielded a rear bagger in perfect operating condition.
Another mower found in the trash was not as fortunate requiring the
replacement of the gear on the crankshaft and the camshaft/camgear
assembly due to broken gear teeth ($35 - it was a learning experience),
carburetor overhaul, and a tune-up.
Assuming the engine doesn't flunk any of these tests, then you may end up
with a functioning mower with relatively little additional cost and effort.
I can only get the engine to idle at a high RPM. If I lower the idle speed,
the engine will eventually die.
Once the engine is started and idling, any attempt to put it into gear will
cause the engine to die. Sometimes it will stay running and I can get the
throttle revved up at which point the motor will push the boat and run just
fine. When I lower the engine speed (approaching the dock) the motor will
eventually die.
I am totally stumped. I've completely rebuilt the carburetor (new seals,
etc.), replaced the condenser, points, and spark plug. I've set all
adjustments to factory specs yet it still won't idle or go into gear."
(From: Al Savage (asavage@iname.com).)
Although I haven't worked in the field in 15 years, two stroke theory doesn't
change much
Is your high idle (out of gear, unloaded) smooth? It shouldn't be. Two
strokes without electronic mixture controls are almost always calibrated to be
slightly rich when unloaded, as the nature of all three induction systems
(piston port, reed, rotary valve) is such that adding a load leans the
effective mixture. Something to do with flow dynamics, I didn't need to know,
as I don't design them.
You've covered the common problem area -- ignition. I suspect you have an air
leak somewhere. Upper or lower crankshaft seal, reed plate gasket, intake
gasket, and upper housing gasket are common areas, in that order.
Mind, this is generic two cycle troubleshooting advice; I don't pretend to
know the model you're working with.
To track these things down in the shop, we'd build custom block off plates and
pressurize the crankcase to a few inches, then watch the gauge to see the
leakage rate. Not terribly practical unless you're rebuilding, but you
sometimes found porous castings and cracks that way.
When I'm feeling adventurous I'd spray starting fluid (with a tube nozzle
attached) around all the seams with the engine running to see if the run
behavior changed. Not recommended; too dangerous.
(From: John Barry (jb@zedak.keepyourspam.com).)
One easy way to tell is to note where port is behind carburetor. If it just
"dumps" into crankcase, like diametrically opposite cylinder, most likely it's
got a reed-valve. If the passage from the carb connects to the cylinder at a
point closer to the crank center-line than the exhaust port, perpendicular to
cylinder axis and perpendicular to crank, it's mostlikely piston-ported. If
the carb passage is parallel to the crank eventually (starts out perpendicular
on Rotax engines), most likely you have a rotary-valve engine; this is usually
the case for serious specific-output.
A quite common problem with these engines is the gasket between the carburetor
and engine. It is usually a thick fiber gasket and sometimes gets blown out if
engine ever backfires. This is more common with age, as the nuts holding carb
on do sometime get loosened. Also gum buildup can and does clog the main and
low-speed jets at times which means removing carburetor. Cleaning out with a
good carburetor cleaner then blowing out all passages. This happens quite
often here where they add 10% alcohol to gasoline. Gas goes bad a lot quicker
than without alcohol!
(From: foxeye (foxeye@www.mindspring.com).)
The best method is if you do not have a flywheel puller is take it to the
nearest Briggs dealer and have them remove it. Since you do have a puller,
just put some tension on the flywheel with the puller you already have, and
then hit the top of the puller (the threaded shaft that centers on the
crankshaft end) with a heavy hammer (16 to 24 oz.) should do it. Sometimes all
it takes is a sharp blow with tension exerted on the flywheel to break it
free. One or 2 raps should be enough. If it fails at that, there are still
other ways to remove it.
Some have points and condenser some do not. There is a points/condenser
replacement kit that makes it solid state available for less than $10.00
called Atomic Ignition. Also rust on the magnet of the flywheel and the
ignition coil laminated portion can also cause it to have no spark. The
measurement is critical for the ignition coil to flywheel space (called air
gap) for proper ignition as well. Unless very badly corroded and worn, the
points can usually be cleaned up and readjusted. Its not uncommon for the
little fiber plunger that operates the points on some models to get stuck.
You should pick up a manual, for proper dimensions, and bolt torque. Even
though it may list special tools for some repairs, there is usually a
work-around in most cases. I would not really spend to much money on this
motor, as the age is against it, but a new one from a source like Northern
Hydraulics can be had for $99 to maybe 125.00. I picked up a 5hp highwheel
lawn mower with a Briggs I/C motor at the end of last summer at a local
builders supply and garden center for $130.00 new in the box.
Last Monday, while I was mowing the lawn, our 21-year-old Snapper mower
quit on me. I could start it up but it would run for a few seconds and
then quit again. After futzing with it in the yard for several minutes I
took it back to the garage, and, after several more attempts at getting it
going, I decided it was likely getting too much gas.
I disassembled the carb and cleaned it good. It's a "PulsaJet" model
with the carb mounted on the gas tank. The diaphragm looked good -- no
visible holes.
I reassembled things and the thing started and ran well enough to finish
mowing, but it didn't have much "oomph".
During the week I got a new diaphragm, and I got around to installing it
today. What a difference!! It used to take several tries to start the
mower, now it starts on one pull. And it has more power than it's had in
years.
Hard to say what may have been wrong with the diaphragm, but likely it had
some microscopic holes in it.
(From: DanDee
If yours is like mine , it has a throttle latch knob to use during
starting. Mine never worked. After pulling myself silly trying to start
it, I just decided to hold the throttle trigger open manually and it
starts every time very easily.
You may want to give it a try if you haven't tried it already.
You might want to check the oil level. Some of the Briggs & Stratton
engines have a low oil pressure cut off. Some of these cutoffs are
very sensitive. They will stop the engine when it's less than a cup
low on oil. As far as I know, you can't adjust it either.
Typically, you remove the entire mowing deck, then manipulate the deck, rather
than the whole mower.
Alternatively, shops often LIFT the whole tractor, and work from underneath.
I built a beam-supported block and tackle affair in my barn to do just that...
it's lots faster than taking the deck off a stupid Murray. Those pieces of
trash require that you remove about a dozen fittings and nuts to get a deck
off.
Now, my Wheel Horse, on the other hand, requires only ONE hand-released
fastener, and off-she-comes!
(From: Al Savage (asavage@iname.com).).
The design is such that it uses an impulse spring to fire at low speed (less
than 10 rpm, yes 10). It does a complex wind spring/release spring action
until the engine fires. Other than the straightforward "replace the
points/condenser" maintenance, I don't think I ever had to have the mechanical
section apart, they're that reliable. I do think I had to clean up a couple
of them, and relube them though.
If you rotate the engine by hand (careful!) you should hear the impulse spring
release, with a very audible bang. With the high tension lead hooked to
your spare-plug-on-the-head, you should be able to have at least 3/8" spark;
less is probably not enough.
If you don't hear that loud bang from the mag, while very slowly cranking the
engine by hand (two turns per bang on that impulse unit), you probably have a
mechanical problem. If you hear the bang, but can't get the mag to fire
repeatably, I'd refurb the points and condenser. It's a bit tricky, and I
haven't even seen one in 15 years, much less worked on one in twenty, but
there are many still in service and parts should be readily available.
Oh, yes. I worked most of my teen years in small engine repair. So I *do*
know whereof I speak. On that vintage equipment, anyway.
Replacement modules are available for many small engines to take the place of
their original point type ignition system. These can be designed in several
different ways but all must emulate the behavior of the point type ignition
replacing just the magneto coil/pole piece assembly and without requiring
alterations to the flywheel.
If you are really curious, check out
U.S. Patent #4163437: Transistor ignition circuit. There are diagrams
of several possible variations on the basic circuit.
(The US Patent & Trademark
Office currently has a search facility with free access to complete text
and graphics.)
Not that any of this profound knowledge does you any good for repair as these
things are usually quite well potted and impregnable.
I once fixed a CDI unit for a 3-cylinder Evinrude 2-stroke outboard motor.
The storage capacitor (1 uF, 400VDC) had a short. Quite simple to replace,
but digging the PCB out of the silicone RTV sealing compound inside the
ignition box was a real pain! But considering that Evinrude charges real
big bucks (about 800 DM = 500$) for the ignition box, it was worth the effort.
Another possible cause of failure of the CDI are the SCRs. Also, check the
charging and trigger windings as well as the cables and connections.
(From: Tom Bellucco (bellucco@netacc.net).)
I recently moved into a new house with a very large lawn and went shopping for
a riding mower / lawn tractor. This is what I was told by various people,
both in and out of mower sales:
Now THAT'S confusion! I'd like to hear what anyone out there knows or has
been told. It ought to be interesting to hear what other stores are telling
people.
Note: The guy that told me that MTD makes John Deere sells Toro and Ariens.
He has publicly stated that he HATES John Deere (I won't post his exact
words). I never realized how defensive a guy gets about his tractor -- you
should have seen the reaction I got when I told a guy his John Deere was made
by MTD! I probably got a worse reaction than if I said something bad about
his wife!!!! Anyway, he got right on the horn to his John Deere dealer and
was promptly told that John Deere makes all John Deere products.
(From: Duane (djdubay@ix.netcom.com).)
Hmph... That *is* confusing. Just make sure that sucker says *Briggs &
Stratton* on the blower cover!
(From: John P. Curcio (jpc@philabs.research.philips.com).)
According to my Cub Cadet dealer (from whom I purchased my snow blower), Cub
Cadet, White, and MTD all come from the same factory. The only differences
are color and features. They are located somewhere in Ohio, near Cleveland,
if I recall correctly.
(From: Carol (carol@willard-oh.com).)
I live just up the road from the MTD plant - never saw a John Deere. I don't
think they do that one.
(From: Peter Szymonik (Xorg@msn.com).)
John Deere makes *all* of their riding mowers. The walk-behinds are assembled
by a "third party", and many Deere dealers don't carry the walk behinds for
that reason, and because the walk behinds had electrical problems.
(From: BELJAN E (lvpy67c@ix.netcom.com).)
HUH??? That doesn't sound right at all. MTD makes that, MTD, Ariens, White,
Cub Cadet, Yard Man, and Lawn Chief. Murray, another famous store brand makes
some of them. Dynamark was and probably still is its own.
John Deer is John Deer.
(From: DeWayne McKay (dmckay@geotec.net).)
You have several people misled on who makes what lawn equipment. I've been
in the repair business for about 12 years now. Murry is made by Murry.
John Deere is made by John Deere. There are several hundred names that
can be found on the side of an MTD product, but MTD does not make any AYP,
Noma, Dynamark, or Sears product. Sears in the late 80's was made by AYP
and Murry depending on model. Now they are only made by AYP. The new line
called Scotts is partially made by AYP. And, as for John Deere: The cheaper
smaller tractors are AYP and the bigger tractors are made by John Deere.
Huskvarna mowers are also made by AYP except a few high-end commercial
models. Also the bottom-end or should I say cheap trimmers and chain saws
from Huskvarna are made by Poulan. Have you ever heard of Gilson? They built
a lot of the Sears products in the 70's and 80's and also built Lawnboy's
tractor line and some of the Ford line in the late 80's.
(Fr0om: Ernest Fields (nodle@centurytel.net).)
Sears still sells push mowers, I bought one this summer and use it for the
trim areas, works great. The only downside is that you have to go to a
professional mower shop to get the blades sharpened correctly.
I bought a Ryobi Mulchinator in '94 (cordless electric). I found it cheapest
at Home Depot, I think it was about $325. I really like it.
Pros:
Cons:
As for the big issue - how does it cut. Well, it cuts pretty well, but it
certainly can't take down anything like a gas mower can. As the grass gets
higher, it starts to leave a bit along one edge of the cutting strip slightly
higher.
If you are the type who knocks a foot off your grass every few weeks, this
isn't the right mower. But if you mow regularly, it works pretty well.
(From: Carol J J (caroljj@ix.netcom.com).)
I have used Black and Decker electric mowers for over 20 years. I Love them.
We have a small property and a 100 foot extension cord is all we need. Since
my husband is disabled, my young sons and I have done all the mowing for
years. There are no worries about pouring or storing gasoline, no pulling
like crazy to get it started. The blade is easy to replace. The grass bag
is awkward but okay. My latest is a mulcher. It switches between regular
and mulching easily. The mulch works well, not as good as a Snapper, but
we're not paying Snapper prices either.
(From: Nann Blaine Hilyard (hilyard@pol.org).)
I bought a Black & Decker cordless electric mower for $150 at Menard's last
year. It is lightweight and very easy to use. I have not calculated the
energy cost (we keep it quietly charging between mowings, though we unplug
it in the winter) versus a gas mower, but I don't have the strength to pull
the cord for a gas mower so the extra electricity doesn't bother me.
(From: Geoffrey G. Shepherd (gshepherd@seanet.com).)
When my old Craftsman gas mower gave up this summer (gas leak) (what, you
didn't read this FAQ?? :-) --- sam), I decided it was time to replace it
with a new electric mower (my brother-in-law has the old mower now and is
working on it for his own use). I ended up purchasing a Black & Decker
CMM-1000 5 HP Cordless Mulching Mower from the local home improvement
warehouse for just over $350.
So far, I'm quite happy with it. It mulches better than the Craftsman did,
and rear-bags when I want to add to the compost pile. It mows my entire
city lot on a charge (in fact, the built-in meter still reads full charge
when I'm done - admittedly, my house takes up a large portion of the lot).
I also like how it adjusts height with one clever lever. It's fairly quiet,
and my clothes don't smell like gasoline when I'm done. Call B&D at
1-800-762-6672 and they can send you literature and a free video on the
CMM-1000.
My only complaint with it is the weight. It seems to weigh about the same
as the gas mower it replaced - it might even be few pounds heavier. But
that's OK - I can use the exercise.
(From: Steve Hill (hills@inficad.com).)
I spent 3 years with a push reel mower. If the blades where sharp and the
grass short then it was fine. If the blades where dull or out of adjustment
or if the length of the grass to be cut at all long, it would leave the lawn
a mess. I'd have to make 2 or 3 passes to get decent results. Also some
types of weeds with resiliant stems where very difficult to cut.
Finally, last year I bought a Black and Decker cordless electric. It was
magnificent. It was a mulching mower so my raking days where over and it
gave much better results. Also, it was very quiet and was always ready to
go in an instant. All of my neighbors with gas mowers were very jealous.
(From: William Lee (w-lee2@nwu.edu).)
I have had a Ryobi for 4 years and found it to be adequate for our small
lawns. It takes me about 20-30 min.to do everything. In my opinion, it
does not cut as well as a "good" gas powered mover that has a sharp blade.
The batteries do degrade over time, although I'm am still working on the
originals. It had an charger problem the first year, but that was fixed
without charge. The blades are non-standard and I have an extra so that I
can have a resharpened blade ready to go.I do enjoy not having to "listen"
to the noise of a gas engine! Good luck!
(From: Andy Dennie (adennie@instinctive.com).)
As a former reel mower user and a current cordless electric mulching mower
user, I can comment on both of these items.
I used a reel mower for about a year and a half. I found that it worked well
if I cut the grass pretty short, but when I did that I got more weeds. I tried
raising the blade height, but then it didn't cut as well.
This year I got a Ryobi Mulchinator cordless electric mower. So far I have
been pretty happy with it. The charge is good for about 1-1.5 hours,
supposedly, but it only takes me about 45 minutes, so I don't know what its
limit is really. It's louder than the reel mower, but quieter than a gas
mower. While charging it can stand on its nose and the handle can be folded
up so that it takes very little floor space in my garage (this was important
for me). One minor inconvenience is that you have to leave it plugged it all
the time (at least that's what they recommend), so it is helpful if you have a
plug near the place where you will store it (you don't want to be tripping
across a long cord all the time). This didn't turn out to be a problem for
me. Another thing is that you're not supposed to store it in very cold
weather (bad for the battery I guess), so I had to move it inside recently
for the winter.
(From: Jim (jstrohm@texas.net).)
The only problem we've had with our plastic-decked B&D is that it tends to
collect grass when it's wet, and clogs frequently. We've chunked a few rocks
with it, but with no damage.
We haven't actually tried to cut rocks with it, and my experience is that a
rock will penetrate the deck of any mower if it hits right. You should pick
up the rocks before you mow, not try to hide from the shrapnel.
In general, electric mowers are best suited for smaller lawns with less
vigorous growth and without extensive landscaping to tangle the cord. A
frequently sharpened blade makes a tremendous difference on electric mowers.
(From: Robert Smits (rs@ham.island.net).)
I've had experience with both electric mowers and gas mowers. I live in
an area where the grass can grow quite quickly and thickly, and the B&D
electric one just doesn't have the oomph to cut long, thick grass. (Even
when you make sure you're using as short a heavy duty cord as is
practical - to avoid voltage drop in the cord). My 5HP gas model just
whizzes through the same stuff, and not having to hassle with the cord
is really an advantage - my lot size is just under an acre.
The battery operated electrics may run out of steam quite soon if you
have a larger lot, and count on replacing the battery pack every few years.
(From: Roger Fillingim (rfilling@uab.edu).)
I've had two electric mowers, both cordless - a Ryobi and a Black &
Decker. The B&D was rated as a 5 HP engine, although I have no way of
knowing whether it delivered the same power as a 5 HP gas mower. I used
my electric mowers on a small lawn. I would agree that the electrics
don't do as well on a overgrown lawn, but other than that my electric,
especially the B&D, were great. I still have the B&D, but I'm in an
apartment right now so I don't have much use for it. But, when our new
house is completed, I plan to use it again.
While charge time and power are potential downsides of electric, not having to
change the oil, fill up with gas, pull a starter cord, etc... are substantial
benefits in my opinion. Also, electric lawn mowers are much quieter and more
environmentally friendly. If your yard is not too large and you mow fairly
regularly, electrics are an option to consider.
(From: Pat Kiewicz (kiewicz@mail.wwnet.com).)
I hung up my reel mower for my Black & Decker rechargeable electric, for the
very same reason. My mower also can bag grass for those occasions when
due to circumstances beyond my control I must cut grass that is too tall or
too damp or when I want grass clips for mulch or composting.
It runs on a lead-acid battery (same technology as your car battery) and
can survive the winter in an unheated garage. I have to go rechargeable if
I want to go electric as my lot stretches back 200 feet or more from the
nearest plug. The battery should last a good, long time if not abused.
(How often do you have to replace your car battery?)
I believe the most recent issue of National Gardening Magazine has an
article on electric mowers, with comparison between the features of
different brands and models.
(From: user@execpc.com (C. Ligh).)
I bought the Toro 24V rechargeable $349 based on the free video tape Toro
provided describing all its features and options. The problem with the
rechargeable is run time.
I have a 10,000+ sq feet lawn and after about 35 minutes mowing the
battery level lights went out. The owner's manual states: one should
stop and recharge after the lights are out or the batteries' life will
be shortened. Anyway there was still power left and I finished the lawn
in about 65 minutes. With the prospect of replacing the batteries every
year and run time shortened after every use, I returned the mower.
Toro does offer a 30 day return. You might want to give it a try when you
have grass. Get the corded model if you don't have too many trees and
save a $100.
When ever my 13 years old Honda dies, I'll probably get a corded
electric mower. But I do miss the quietness of a electric and absence of
exhaust fume.
P.S. There is a 36V rechargeable, but it's a $100+ more. So, will replacing
the two batteries = $200?
(From: Michael Lamb (michael.lamb@nciinc.com).)
I own an electric mower now. It's a beefed-up Sunbeam. I found it on the side
of the road and did a bit of 'customizing' to it. I like it MUCH better than
the gas thing I had for years. The cord is a bit of a bother but when I think
that I'm polluting far less and it uses far less power (costs about 25 cents
less energy to cut the yard compared to the old gas one) AND it doesn't stink
and be a pain to start and a health hazard and is quieter too. I might get a
new cordless eventually but the $375 price tag is a bit much. I tried one out
and think they are pretty nice, far lighter than a gas mower. Besides the one
I have does very well for now. A friend of mine bought a B&D cordless, she
likes it and has no problem doing her yard and her neighbors too! (she likes
cutting grass)
(From: ap052137@idirect.com).
Have really enjoyed the convenience of a cordless mower. Bought it in 1992 and
went to replace the battery. It is a model 3300m and got the shock off my life
when the first place I tried quoted me a price of approx $236 cdn. I got in
touch with B&D and they directed me to another dealer where I got it for
$93. However, this dealer told me that the new price list does indeed show
$236 cdn for new stock. Goodbye B&D the next time the battery needs replacing.
I can buy a complete gas or ac unit for the amount of money.
(From: Mike).
The problem you state does not exist for only B&D lawn mowers, but *any*
rechargeable product. Batteries do not last forever, and typically account for
more than 50% of the cost in any tool. Often times the batteries are a
standard size and you can get relatively inexpensive replacements
at electronic stores. As an example, most cordless drills use sub 'C' cells
which run about $1.75 a piece from Tanner Electronics in Dallas, Tx. For
comparison, B&D wants $20 for their replacement (four batteries).
At the risk of sounding like a zealot...the people that think they are "saving
the environment" with their electric lawn mowers are fooling themselves. In
the first place, all you've done is moved the pollution from your backyard to
somebody elses, and soon we're going to extend this fallacy to cars (oh,
joy...smog in the country). In the second place, the process used to produce
Cadmium plating is so toxic that even the US military is phasing out its use,
while most foreign (non-US) governments outlaw its production entirely.
"Green factor" wise, we're all probably just as well off with oil burning
tub-thumpers.
I predict in the not so distant future (10-20 years) we'll see the end of
NiCad powered appliances either because governments ban them, tax the
daylights out of them, or nobody will be dumb enough to build the batteries
anymore. At the very least, expect to see mandatory recycling programs for
*all* types of batteries (not just lead-acid). Regardless, prices will sky
rocket.
Ok, soap box mode off :).
(From: J. Matthew Good (jmg14213@ix.netcom.com))
First, battery powered lawn mowers use Lead - Sulfuric acid batteries, just
like in your gas powered car, only smaller. Second, these batteries are one
hundred percent recyclable. Yes, that is 100%.
To the original poster: The only problem with battery mowers is that you must
follow the directions about over- charging. Also, they are sealed, as most of
them are installed laying on their sides, so ordinary replacement batteries
would leak.
Ryobi has replaced the pair of batteries in their machine with a single 24V
unit which lists for about $95 US, PLUS FREIGHT. From what I've seen, they are
lasting anywhere from 2 to 3 years for most users. To make it last longer,
charge only until the indicator says it is fully charged, then unplug it. On a
Ryobi, the light turns from red to green to indicate full charge, and
supposedly goes into float charge. Don't take a chance, when it turns green, or
whatever Black and Decker's equivalent is, Pull the Plug.
(From: Ronald Kramer (kramerr@oasys.dt.navy.mil).)
This is my third year with a so-called 5HP Black and Decker battery electric.
I think they are crap! I couldn't mow the lawn due to rain this weekend once
again so the grass got to be twice the cutting height. This requires that I
cut without the bag which causes the grass to clump. I then have to go over
the area again with the bag. For my 12500 sq. ft. yard takes 4 days because I
have only 50 min of charge. So when I finish I have a yard of grass at
different heights and it is time to start mowing again.
(From: Jeff Canavan (Canavan@foodfac1.rutgers.spamfree.edu).)
I recently had the decision to make regarding a new lawn mower. I went with
all electric stuff for the yard; corded combo weedwacker/edger, 16" chainsaw
and Black and Decker CMM1000 rechargeable lawn mower. Searching through prior
usenet posts with Dejanews.com, I found mostly good comments about the lawn
mower and thought I'd give it a try. It comes with a 30 day money-back offer,
so if I really hated it, I could return it to get a corded one or a fume
belching fossil fueled model. After plugging it in overnight, I mowed the
grass for the first time last Sunday, (it hadn't been mowed for 7+ weeks)
After mulching the 1/2 acre of shin- to knee-high grass and weeds, the charge
indicator was still in the green zone halfway between the Fullest and the
yellow. The box states 1/2 acre range, including driveway, walkways, and
house. It must be conservative or I got a really great set of batteries.
Discounting all ecological debates regarding macro pollution issues;
Pluses:
Pluses, neutrals, or minuses, (depending on your view of yardwork):
Minuses:
(From: Frank Wilder (frank.wilder@intrlnk.com).)
We have an 18" rechargeable Black & Decker electric and we really like it. We
bought a refurbished unit at a Black & Decker outlet.
Pros:
Cons:
I am happy with the one I have but I can't wait to upgrade to a bigger
one. The newer B&D lawn mowers look really great.
(From: Dave Clark (Dave_Clark@dg.com).)
Country Home Products, the people who make the DR Field and brush mower
offer a cordless lawn mower that has a removable battery. The battery has
a built in handle and lifts out of the mower housing for easy replacement
and charging. If it is half the quality of the DR Brush mower it is a
great mower, and a great company to do business with. They are located in
Vermont, and you can get their number from 800 information
(1-800-555-1212).
I don't own the mower (yet) but am considering it for my mothers house. I
do own the DR and I love it. I have no interest in this company - but I am
a very satisfied customer.
(From: Topher Eliot (eliot@alum.mit.edu).)
I'm happy with my Sears electric. I discovered on trick for dealing with the
cord: use a heavy duty, long cord (100', 12-gauge in my case) with a short
light cord at the end (20' 16 gauge). This allows moving back and forth a
moderate amount without having to move that heavy cord.
BTW, I don't think I really needed that 12-gauge; in retrospect a 14-gauge
would have been better.
Mulching mowers are nice, you don't have to bag any of the grass that you cut.
Mulchers do need a bigger engine, that's why if they are used to mulch make
sure it is at least a 5 hp 21" or less ( 6hp for a bigger cut).
Mulching adds moisture and acts as fertilizer for the lawn.
The bad thing is that you need to cut the lawn every four to five days. If the
grass gets too long the mower can't cut the grass as well as it should (also
it's not good for the grass if you cut off more than a inch at a time that is
when the mower is set at 3 inches). So for that reason it would not look that
good if it was to rain a lot and you could not cut the grass.
As for me I have both types that works out very well.
"The problem with Murrays and MTDs is that they use the cheapest engines and
components available. If you manage to get the engine to last, the rest of
the mower will fall apart around it. Remember, the reason K-Mart, Lechmere,
Caldor, and other mass merchandisers sell these machines, is because they
want you to come back every 2-3 years to buy a new mower from them."
"Murray is a bargain basement brand sold by mass merchandisers who want you
to come back for a new mower every 2-3 years, and Tecumseh engines at about
the same. :-( If you manage to get the engine to last, the deck will fall
apart around it. On the bright side, at least they are cheap."
Some responses:
(From: Jan Hickman (janry@ix.netcom.com).)
Yea!! My bargain basement (cost under $100 when new) Murray is over 10 years
old and I'm cutting .4 acres with it. You can bet when it wears out (if it
ever does) I'm gonna buy some mega bucks mower!! But if you do take that
bet, let me in on the other side of the action.
Keep the blade sharp, the air filter clean, topped up on oil and they will
run for a looooong time.
(From: Don Sterner (No@junk.email).)
Well, my Murray has a quality Briggs & Stratton engine which is still running
fine. My problem is that the deck has rusted and is now a shell of its former
self. There is barely enough metal left to hold the blade shafts in place.
The mower is only 2 1/2 years old, but we do live on salt water (next to it,
really). All of our property is well above the water line - the mower has
never been wet with salt water. I've made it a practice to always hose the
mower down after use and I keep it under cover when not in use. The only
replacement decks I can locate cost nearly as much as a new mower.
Our previous mower (a Craftsman) was returned to Sears within 6 months after
it had lost much of its paint and was covered with rust.
(From: BELJAN E (lvpy67c@ix.netcom.com).)
My MTD mower holds up fine, and I have the killer lawn. It burns out virtually
every lawn mower's engine, whether it is Briggs or Tecumseh. I bought my MTD
and it is a self propelled with 3.75 hp Briggs & Stratton Sprint engine. I
would buy the same mower again, the problem is I probably wouldn't need to!
The mower is so durable, it is unbelievable (I should note it is last years
front cog drive which now is 4 hp quattro, and it is still sold with the 3.75
HP engine as Lawn Chief.) It survived a year and still doesn't burn oil!
That is a major accomplishment. The only trick is to put Marvel Mystery Oil
into the gas and oil. I also have a 16 year old Snapper and it still goes.
Regardless, MTD is well worth it. You get a cheap mower that in my estimate
unless you abuse it will last 5 years or more with good maintenance. $100 or
so for 5 years of use (and it isn't hard to maintain them) is an excellent
deal. A $600 mower could last less than that.
(From: Floyd Reed (floyda@ix.netcom.com).)
If you take care of amy mower, you can expect a reasonable amount of service
out of it, usually comparable to the price. True, Murray mowers are cheaply
built, but they build an awful lot of mowers... with different name brands.
Most still carry a substantial warranty. As for Tecumseh engines, years ago
they were the more expensive engine, placed on the more expensive machines.
They were the only engine of this type and size to incorporate an actual oil
pump. I never did care much for them as they liked to burn exhaust valves
and blow head gaskets. The carburetors left a little to be desired also.
They were good for my small engine repair business. I am out of the business
now and have not taken one apart for a long time and do not know how they are
being made today, but I'll bet if you take care of them and change the oil
regularly as well as keep the air cleaner clean, you will receive respectable
service out of it.
(From: Jan Hickman (janry@ix.netcom.com).)
My Murray with a 3.5 HP Tecumseh engine is over 10 years old. The only parts
replaced have been the wheels, the spark plug once and the blade a couple of
times. The lawn area I cut is approximately 1/3 acre. Will I ever buy a $500
quality lawn mower? Not as long as I can get one to last like this. And by
the way - it's not luck, it taking care of them. I know several people whose
bargain basement brands last several years and they all have one thing in
common. They take care of them."
(From: Patrick J. McQuiggan (PMCQUIGGAN@cardinalfinancial.com).)
I've had a Murray since 1990. No problems whatsoever. Also 1/3 acre. Use
it regularly. Follow maintenance advice. Engine is Briggs & Stratton 5 hp
and it is self propelled. A bargain.
(From: Bijan Mobasseri (mobasser@vu-vlsi.ee.vill.edu).)
I am amused with the high power recommendations here: Honda, Toro, Snapper,
Lawnboy, some costing $600. In 1989 I bought a walk-behind Murray for $99.
This morning, as in all Saturdays, I pulled it out of the shed, gave it ONE
pull and as always it started. It is still running on the original
plug (Tecumseh engine) and the only thing I have replaced is one $5 wheel.
I've got a non-propelled high-wheel, it's okay. Nothing very exciting. My
lawn is hilly but not bumpy, and I had gotten the high-wheeler to assist in
shifting over edging and over flag walkways, and it's okay for that - but
not so great that I'd bother with a high-wheel design in the future.
What I would *love* to get in the future, and maybe that 'weed whacker on
steroids' is what I really need, is something that would let me go casually
over edging, so the blade is cutting grass on one side and safely *not*
cutting 1 to 2" river stones on the other side. This is made worse because
the left-hand wheels on the stone (typically, with a right-throw mower)
jiggle up and down enough that the occasional stone does get whupped.
I'd also be interested, if anybody makes one, in an *offset* mower, in
which the left-hand wheels were not to the left of the mower housing. By
increasing the wheelbase and putting one fore and one aft, I would love for
the left side of the mower to be cantilevered out with nothing under it
but the blade, to let me get really close for edging. I don't want a
specialized edger - I want a mower that can do the job through the simple
expedient of getting the left-side wheels out of the way!
I bought a new Honda with a plastic deck. I like it. The plastic is not like
regular plastic; in fact, it has proven bulletproof. It is very lightweight.
I mowed many rocks, keys, etc. with no problem. It was a concern of mine when
I bought the unit ($660), but the salesman convinced me that it was 'put
through hell' to prove its vitality.
I have always preferred Tecumseh engines over Briggs & Stratton though perhaps
this is more of a touchy-feely thing than representing any really fundamental
difference between the two. The float carburetors (e.g., Craftsman) do tend
to gum up if the gas is not drained at the end of the season but they are easy
to clean and rebuild. (Also, I have picked up several mowers dirt cheap at
garage sales where the only problem was a gummed up carburetor - 15 minutes
work to remedy.) Change the oil regularly and Tecumseh engines will keep
going for a long time.
(From: BELJAN E (lvpy67c@ix.netcom.com).)
What a JOKE!!! Try rebuilding a '72 carb sometimes, the floats are terrible,
I finally slapped a '91 4 HP carb on the 4 HP '72 and it works now!!!! Some
newer ones can be saved, but 10 years of sitting with *leaded* gas, that
spells the end.
(From: Sam.)
Hehehe... A guy just sent me a couple of carbs that were probably closer to
'72 than '91. A new needle, seat, and hinge pin (in one case) was all that
was needed (beyond the gallon of carburetor cleaner!). :-)
(From: BELJAN E (lvpy67c@ix.netcom.com).)
It depends on how the gas was in, if you drain the float, you should be able
to get it clean. Another trick is to put Marvel Mystery Oil in the float
assembly and let it sit there a week, in 99% of cases, that will get it
running. On the '72 carb, The gas formed crystals around all of the parts,
I put all sorts of carb cleaners in, and I replaced the rubber seal, float,
needle, and all replaceable parts, it didn't work. I pulled the carb off
(this happens to be a '72 Tecumseh off a Sears engine. My guess is that is
was overhauled so I got it starting on one pull with starting fluid). I took
a '91 Sears (Tecumseh) carb off and bolted it onto the engine, since this
is a power reel mower, the engine isn't easily replaced, the new carb is from
a primer type non-choke engine, so I made a rubber plug in the hose to the
air filter assembly to spray starting fluid into the carb to start it. Now
it works fine. It looks strange but runs great!
(From: Thomas N. Harding ( harding@coypu.cig.mot.com).)
I would like to add that Tecumseh engines are easy to rebuild. Most
folks would be surprised how few parts are in them.
(From: Steve Ordinetz (steveord@xtdl.com).)
Several years ago I worked with a guy who rebuilt small engines as a sideline,
and he was partial to Briggs & Stratton because parts tended to be pretty
standard from year to year, while Tecumseh were less interchangeable between
similar engines of different vintage.
(From: Terry Highley (terry.highley@daytonoh.ncr.com).)
I agree 100%!!!
(From: BELJAN E (lvpy67c@ix.netcom.com).)
Ha! I have had no trouble forcing Tecumseh engine parts to fit on same
horsepower engines, and they all worked fine, I had spent over 30 minutes
starting one with stale gas once though!
(From: jakdedert (jdedert@bellsouth.net).)
IME, Briggs motors are much more 'finicky' for starting and maintenance, but
they last longer and use much less gas and oil.
The Tecumseh's (I have two of those, and one Briggs & Stratton) start much
easier, although that's probably due to the priming bulb which my Briggs
does not have. They start using oil right out of the box, however. I have
to check and add oil on almost every use. My Eager1 uses almost twice as
much fuel to mow the same yard as my older Briggs of the same horsepower and
cut width. I almost never have to add oil to the Briggs in an entire
season.
Given the greater oil and gas consumption, I assume that the Tecumseh's are
emitting considerably more pollutants per hour of use. The consumables only
add a negligible amount to my lawn-care costs every year; but multiplied by
(however many millions) of them out there.....
Any thoughts?
(From: James Sweet (jamessweet@hotmail.com).)
Well it's hard to say these days, back when I was tinkering with this stuff
a lot I was dealing with engines made mostly in the 1970's and the Briggs
motors were very noticeably better made and easier to work on. The
Tecumsehs' were nothing but a pain in the ass, carb problems, ignition
problems, a few common models would regularly throw rods. It was no shock
since they were always about 40% cheaper than a comparable B&S. Now days I
don't really know, the Tecumseh engines seem to have improved somewhat,
while the Briggs engines have gotten *very* noticeably poorer. Somebody said
they're now made in Asia so perhaps that's when the quality took a dive. BTW
the new ones do have a primer bulb, haven't tried starting one though. My
mom has an old mower with a Tecumseh and it does actually start quite easily
though I have to take apart the carb and clean out the banjo bolt on the
float bowl every year, never had to do that with an old Briggs. Unfortunately
I never compared fuel consumption but I don't recall oil usage problems on
either.
(From: Vampyres@nettaxi.com.)
Yes, there was a time when Briggs were better engines.
Not so anymore. B&S has gotten into the parts game. They make nearly
as much profit on parts and service as they do in the initial sale.
Tecumseh had to rethink their whole market strategy in the late 70's
and refocused on building better quality engines that were certainly
more standardized. On virtually every Tecumseh vertical shaft engine
the carbs and coils are interchangeable, unlike Briggs where every
engine requires a particular model coil or carburetor-setup.
Odd that your Eager-1 (Sears) mower uses so much oil. I'd say it might
be just the particular engine as virtually none of the ones I've used
or serviced ever developed this problem during their useful life.(Cast
iron sleeves and 2 oil rings unlike the single ring in Briggs and the
cheap alloys used in both the sleeve and ring.)
The poorer, cheap design in the Briggs carbs make for a much worse
problem in regards to pollution as they tend to run rich with just a
little age.(I've seen some come into my shop that are running so rich
that they actually wash the cylinder. This results in excessive wear
on the sleeve and rings, allowing bypass into the crankcase. Once the
oil is broken down by the gas it'll bypass the rings and the result is
a smoking engine.(great if you want to fog your yard as you cut it.)
Tecumseh carbs are actually easy to operate and care for once you
learn some basics.
They're float style carbs and as such you can't just run 'em and
forget 'em. leaving gas in the carb and tank off season is the worst
thing you can do. (Most people don't realize that gasoline actually
goes bad with time and actually expect a mower that's sat unused for
six months to just crank up on the first pull.)
Run the tank dry at the last cutting of the season then loosen the
Bowl nut and drain the gas out of the float bowl.(It's easy, all it
takes is a 1/2 inch socket to loosen it.)
Then leave it dry for the winter, DON'T put any type of winterizer in
it. Worst stuff in the world. Just ensures you'll be taking it in for
a carb job as the stuff just turns to jelly and will make a real mess
of your carb and tank.
There's just no way to "preserve" gas, use it or lose it.
If you want proof as to Tecumseh's quality over Briggs just look at
how Briggs has copied Tecumseh design.
Tecumseh has the best design in a starter recoil mechanism hands
down, Briggs finally gave up using their ball bearing starter clutch
mechanism on all their 5 hp or larger engines and copied the Tecumseh
design out right. (But it's still not as good.)
They went to a float style carb but picked what is in my opinion one
of the worst makes, Walbro.
I tell all my customers if they insist on a Briggs, just get one of the
Sprints, either a 3.5 or 4 hp model, and don't expect much more than 2
years of use out of it. I have some customers still using the same
Craftsmans mower with a Tecumseh engine for 10 years or longer.
I gave my in-laws one of my personal Craftsmans that I purchased back
in 1982 and it's still going strong, with NO major engine work at all.
(From: Sam.)
My $35 garage sale Craftsman mower with the basic 3.5 hp Tecumseh
engine is still going strong after 24+ years. The ignition module went
bad a couple years ago (replaced from junk parts I had), and the carb
needed cleaning once. I do usually try to remember to drain the
carb after the mowing season but it doesn't always happen. :) Aside
from those problems, it still usually starts on 1 pull.
I have used several Ryobi 15" grass trimmers over the years and I've
learned a few things in the process. Every now and then, they just
simply will not crank. A good spark plug cleaning will remedy that.
Also, apparently their 31 cc engine is not big enough, or other aspects of the
machines are not heavy duty enugh to handle those 3 metal bladed cutters
some places offer as "after market" wonders. I have used two of them
over the years and both times it was disastrous to the trimmers.
The heavier 0.105" 4 sided red cutting line does a great job on these
trimmers. It cuts much better than the 0.080" round line and lasts much
much longer. You have to open up the holes in the cutter head to make
the bigger line fit but that is no problem. Unless, of course you
decide to go back to the smaller line later.
I recently damaged the engine on my Honda mower, so here is my experience
(Seattle area):
The engine is well built and fairly easy to work on. Their manual specifies a
bunch of special tools, but I was able to take the engine apart and put it
back together with just "ordinary" small engine tools. The only problem I had
was with the flywheel. It has no threaded holes, and needs to be held around
the periphery with something like a belt-wrench while torquing the center
bolt. For the same reason, a large gear-puller is required to remove the
flywheel from the crankshaft. I did not attempt anything ambitious like
replacing valve seats, though. All threads on this engine are metric, of
course.
The manual (available from dealers) is very clear and well illustrated. Carb
rebuilding is not covered, however. Part numbers are listed in a special
"parts manual", not in the regular one.
Note that Honda appears to have a policy of not letting anybody but their
dealers get in touch with their central tech support. They don't publish
their phone number, and there is no email address either. I could not find
the timing mark on the crank, and the dealer could not or would not help, so
guessing was the only option left... I don't know if other small engine makers
are any better in this respect, but I am used to customer support meaning
something entirely different in my line of work.
No trouble getting parts, but they all had to be "special ordered" from out of
state, taking about a week to arrive. They seem very expensive to me. A rod
was $50+, a set of piston rings, valve springs, or head gasket $20+ each, and
the crank (which I luckily ended up not needing) was supposed to set me back
about $185. My relatively minor repair ended up being about $125 in parts
(taxes, oil, and band-aid for bruised knuckles not included).
The mower has served me well, and the only problem other than caused by my own
fault was premature wear of the blade clutch lining. The plastic deck seems
to take rock hits much better than an aluminum deck that I owned some time
ago, and there is no paint to peel of from it.
The forward speed is about the same for a walk behind and a rider, about 3
mph. The main variable is the width of the mower. Let's say we have a
42" mower. If the overlap is 4", then we have 38" cut.
Then the time to do one acre with a 42" mower is:
220 ft. x 220 ft. / ( 3.17 ft x 4.4 ft/sec x 60 sec/min) = 58 minutes.
In summary:
You can go faster with a rider, but the quality of cut degrades. The
walker gets slower for a large lawn since one gets tired and takes more
breaks and tends to slow down on the turns.
I would recommend only a tractor that had a cast iron engine and a rear
discharge mower. I had a tractor with an engine with aluminum heads. The
first engine failed and I replaced it and the second failed. They both
warped and eventually failed. I got a tractor with a cast iron engine and
it never quit. Eventually it got so old that when the fuel pump failed,
it could not be replaced. Now I am using a WheelHorse/Toro with a 17 HP
Kohler 2-cylinder cast iron engine. It is a great machine and has worked
flawlessly over 12 seasons. The 17 HP is excessive for mowing or pushing
snow, but the 2-cylinder engine is great. I can mow for 5 hours and not
get the least bit fatigued. However, with 1-cylinder engines the
vibration was so great that my toes and fingers would become numb in less
than an hour. I had to take a break every hour to recover.
For the mower, get a steel rear discharge mower. The first mower I got
was a cast aluminum mower. Every rock the mower picked up knocked a chunk
out of the housing until there was nothing left. Then I got a steel
mower, but the aluminum engine gave out and it was not prudent to get a
third engine for the steel mower. I did get a tractor with a cast iron
engine that could use the steel mower and this combination lasted 20
years.
Now on the WheelHorse/Toro I got a rear discharge mower because it does
not throw objects like the side discharge machines. Also, when the grass
clippings are too heavy to leave on the ground, I can collect them with a
simple sweeper and not need a motorized collection system. Also, it
doesn't throw clippings on the flower beds and walks or make passing
motorists think they are going to be attacked. It is also easy to mow
next to shrubs and trees on either side of the tractor. You don't have to
always mow with the discharge to the mowed or unmowed side, depending upon
what you are trying to accomplish.
(From: ranck@joesbar.cc.vt.edu).
I don't have one, but apparently the CIA has two. They use them in a
courtyard that is completely surrounded by one of their buildings. The
robo-mowers were seen as a better solution than having to have a security
officer escort some person in/out and watch them mow.
(From: Andrew Bowers (falcon_@geocities.com).)
I just did something cool!
My friend Dan gave me a 3.5 HP Briggs & Stratton horizontal shaft engine,
which burned oil like crazy. I took it completely apart, (Dan had started to,
but he hadn't taken the actual block apart, he had just taken the carburetor,
muffler, and flywheel cover off) and found a _deep_ gouge in the cylinder
wall. The rings were fine, except there was a chunk missing from the oil
ring. Here comes the "miracle" part. Most people would have just chucked the
engine, or kept it around for parts. I grabbed my thing of JB Weld ("the
world's finest cold weld"), mixed some up, and filled in the gouge. The next
day, I sanded the patch smooth, and put the engine back together. Started on
the first try. Still burns oil (due to the missing segment on the oil ring;
the auto parts store I went to didn't have piston rings, can you believe
that?), but runs pretty good. (Well, the injectors in the carburetor keep
getting clogged, and it won't start, so we're going to get a new, *plastic*
gas tank).
When I was 17 and still living at home, mowing the lawn was part of my
chores. Well, I didn't have a running lawn mower and my Mom insisted that I
mow the lawn. She pretty much stated that she didn't care how I did it, as
long as it got done.
So, I figured that I needed to get one of them running, and I couldn't
for the life of me figure out what the exact problem was but I wasn't getting
spark, so I figured that it had to be the magneto. Well, I didn't have the
resources to get a new one, so I did the next best thing, I rewired it!
Mom comes out to find me mowing the lawn with a car battery and a coil
strapped to the thing. Ran a line from the condenser to a spare coil I had
for my VW Bug and strapped an AC/Delco to the thing and away I went. It was
a bit heavy but it was better than nothing. I still wish I took pictures of
it.
(From: Charles Gilley (gilley@bravewc.com).)
My coolest repair was rebuilding my B&S after letting the oil run out. After
I put it back together and with great anticipation, I began to pull and pull
and pull.... I was impressed. It was silky smooth, but the darn thing would
not start. I sat down to rest, glanced at the bench... to see the valve
lifters still sitting there.
Sigh.....
My father-in-law owned a Flymo with a 3.5 HP Briggs & Stratton. He'd had
it for nearly twenty years, but never used it much because it was "hard to
start", especially when hot. He has other mowers and neither of us had
found time to investigate it. Why he didn't return it for warranty
investigation at the start is lost in the mists of time.
This year, he felt it was taking up space in his barn and was going to
throw it away, so it was rescued by yours truly. I thought the motor might
be a useful standby in case the even older Aspera (European Tecumseh) on my
own rotary packed up. That's been a fine engine, by the way. The B&S was
in a pretty good state considering, but sure enough took up to fifteen
pulls to start when cold and would not re-start at all if fully warmed up.
It did look like it'd been HOT, with the usual blockage of ventilation
spaces by clippings, but otherwise well preserved.
I gave it a complete carb and magneto overhaul which improved cold starting
somewhat, but not the hot. I also felt it was a bit "gutless", so then
investigated the combustion chamber and valves. This poor machine had
virtually NO valve clearance when cold, on either lifter. The valves were
still in pretty good order, so my assumption is that it was shipped that
way from the factory. Once it got hot, the compression must have been
zero, though it didn't obviously seem to be.
A thorough clean, careful adjustment of the valve stems with a diamond
hone (out of the engine !! ) to provide the upper limit of the specified
cold clearances and back together it went. What a contrast ! It now
starts first pull, hot or cold, and runs like it should have done when it
left the factory. My guess is the magneto and carb were fine all along in
this lightly-used engine. Next time I'm going to look at those valve
clearances earlier in the sequence, even if the engine isn't old....
You don't adjust OHV engines at TDC. You must bypass
the compression release by turning passed TDC and
letting the piston drop 1/4". Using a plastic ball
point pen as a tool in your spark plug hole you can
let the piston push the ball point pen out of the
spark plug hole till it starts returning inside the
cylinder. Make a mark on the pen so you can
see the 1/4" drop of the pen. Then set your valves
at 0.004 clearance for both IN/EX. Note: This is a general valve
clearance specification that covers most engines today. Check
your maintenance book or ask your local dealer for the
info on the valve clearance for your specific engine.
Nearly all small engines up to 20 HP or so are single cylinder affairs - one
piston, one spark plug, no distributor, forced air cooled - about as simple
and straightforward as it gets.
If you have never been under the hood of your automobile, then the description
in the following sections may be of some help.
The next chapter: "Engine Diagrams" provides an explanation of each of the
4 strokes of a 4 stroke engine. However, if you cannot get the hang of my
fabulous ASCII graphics, check out the following site:
The How Stuff Works Web
site has some really nice introductory material (with graphics) on a variety
of topics relating to technology in the modern world. Of relevance to this
document is an article on "How Car Engines Work" which is really mostly
about the basic principles but WITH some real animated graphics!
The small 4 stroke engine has a separate oil sump just like the engine in
an automobile. Therefore, gasoline and oil are separate. Oil changes are
also required.
WARNING: a new lawn mower or other piece of yard equipment will very likely
be shipped without oil or just a minimal oil fill. Check it first and add
oil if necessary. Running an engine without oil for a few minutes can cause
serious - or terminal - damage. Even if your mower was assembled by the
store where you bought it, don't assume they filled it with oil and tried
it out!
The 2 stroke engine requires that the gas and special oil be mixed prior to
use in specific proportions. Leave out the oil - or get your gas cans mixed
up - and you will quickly ruin a 2 stroke engine due to lack of lubrication if
plain gas is used by mistake. Clearly label the gas cans for each type and
instruct anyone using them in the proper fueling technique.
Portable tools like chain saws, weed whackers, and backpack type leaf blowers
use 2 stroke engines as these need to operate in a variety of positions.
Stationary or wheel-about equipment including most lawn mowers, rototillers,
shredders, backup electric generators, and large blower/vacs, use 4 stroke
engines.
Another distinction is that engines smaller than about 2 horsepower are
generally 2 stroke while those larger than 2 horsepower are generally 4
stroke but there are exceptions. Lawnboy lawn mowers tend to have 2 stroke
engines and there are some types of equipment with very small 4 stroke
engines. Of course, if your engine has a cap marked 'oil' then it is a
4 stroke.
Larger pieces of yard equipment like riding mowers and lawn tractors use
4 stroke engines that are really very similar in most respects to their
smaller cousins - much more so than to the engine in your automobile, for
example. Similar servicing procedures apply. In fact, if you read the
respective chapters in any of the engine repair books for engines (listed
in the section: References) under 5 horsepower and
those between 5 and about 20 horsepower, the only significant differences
will be in the size of the various engine parts!
Several functions are incorporated in a carburetor:
Craftsman and Lawnboy carburetors use a float similar to the system used
in automobile engine carburetors (when they still used this technology).
A hollow float maintains a constant level of fuel in a reservoir called a
float bowl by acting against an inlet needle valve. The fuel tank will
usually be above the level of a float carburetor though a fuel pump could
also be used. See the section: Basic operation of a
float type carburetor for a more detailed description and diagram.
Where equipment may be operated in any position, a diaphragm carburetor
is used. A flexible disk (diaphragm) with atmospheric pressure on one
side and intake pressure on the other is used to maintain the proper
air-fuel ratio (this is a gross simplification!).
Briggs & Stratton engines usually have a suction lift carburetor with
a built-in fuel pump. Some simple ones don't even have a fuel pump but
depend on suction alone to pull gas from the tank. In both cases, the
fuel tank is usually below the carburetor. If there is no fuel pump, the
fuel tank should generally not be less than 1/3 full for proper operation.
A soft metal key locks the flywheel to the crankshaft. This is designed
to shear (break) to protect expensive engine parts should the engine stop
abruptly (due to blade of a rotary mower striking an obstruction, for
example). In this case, the flywheel inertia will attempt to keep it
moving and it is better to shear the key than to fracture the flywheel
or crankshaft.
For other types of equipment, various adapters are used to couple the
driven device to the engine crankshaft. These may include gear reducers or
multispeed transmissions, belt or chain drives, or a direct connection to
a blower, vacuum, or pump impeller, or electric generator or alternator.
As with the blade adapter, a soft metal key or shear pin will likely be
used for protection.
Note that in most small engines, the valves are not mounted above the
cylinder (in the head) as they are in automobile engines. Rather, they
are mounted on the side of the cylinder in the engine block. This is
done for reasons of cost requiring fewer parts and simpler construction.
The cylinder head is then just a casting with cooling fins and a threaded
hole for the spark plug. The disadvantage of the side valve engine is
lower efficiency and higher pollution. The newest (and currently most
expensive) lawn mowers and other yard equipment are incorporating the
better overhead valve technology. Eventually, environmental protection
laws may force this on all small engine operated devices. However, both
types can apparently be made to meet the emissions standards mandated
for all new mowers sold after September 1996.
All other important parts are lubricated typically by one of the following
devices:
With both types, increasing the spring force will increase the engine speed.
The type of engine in your lawn mower or automobile operates on what is
called the 'Otto' cycle (if you care). A complete 'cycle' is needed to
supply one power impulse to the output shaft. All engines must provide
the following regardless of whether they are 2 stroke or 4 stroke, rotary,
or turbines (though turbines or jet engines operate in a continuous rather
than pulsed manner):
For the following, refer to the section: The four strokes
of a four stroke engine in living ASCII art.
4 stroke: The air-fuel mixture is sucked into the cylinder through the
open intake valve as the piston moves downward on the intake stroke.
4 stroke: Both valves are closed. The piston moves upwards thus reducing
the space above it and compressing the air-fuel mixture.
4 stroke: Both valves are closed. The heat produced by the rapidly
burning gases to expand and drive the piston downward and because it
is connected to the crankshaft, drives the load as well.
4 stroke: The exhaust valve is open. The piston moves upward and pushes
the exhaust gasses out through the muffler.
A relatively massive flywheel attached to the crankshaft provides the inertia
to allow the engine to coast through the non-power strokes (1-3). However,
this is not always enough by itself - the blade on a rotary lawn mower is often
required as well and a rotary mower may not start easily if at all without the
blade in place and tightened securely.
Note that the terms '2 cycle' or '4 cycle' are often used incorrectly when
what is meant is 2 stroke or 4 stroke. The cycle is the entire sequence of
events including intake, compression, power, and exhaust. The complete cycle
for a 4 stroke engine is two complete revolutions of the crankshaft. The
complete cycle for a 2 stroke engine is one rotation of the crankshaft. This
means that a 2 stroke engine produces a power stroke on every rotation
of the crankshaft while a 4 stroke engine does this only on every other one.
Thus, a 2 stroke engine will be more powerful than a similar size 4 stroke
engine. However, on the down side, 2 stroke engines tend to be less efficient
in fuel utilization and pollute much more than 4 stroke engines.
The bearings to be concerned with in a lawn mower or small engine are:
A variety of bearing types are available. For most inexpensive rotary lawn
mowers, plain bearings are most popular due to their simplicity and low cost.
The shaft of a small engine is made of steel though other materials may be
found depending on the particular needs. Where a metal bushing is used,
there must be a means provided for lubrication. In a small engine, this is
provided by the engine oil via a variety of means. For example, a typical
Tecumseh lawn mower engine lubricates the blade end/PTO main bearing by
direct immersion in the oil sump, the magneto/flywheel main bearing via
machined passage fed from the camgear driven oil pump, and the crank pin
journal by oil sprayed or dripped from above.
Under normal conditions, a plain bearing wears only during start and stop
cycles. While the shaft is rotating at any reasonable speed, there is
absolutely no metal to metal contact and thus no wear. With a properly
designed and maintained bearing of this type, a very thin oil film entirely
supports the shaft - thus the importance of regular oil changes to assure
clean oil with effective lubricating properties.
To put this into perspective, the clearance between the connecting rod and
crank pin journal of a typical small engine crank pin journal may be
0.0005 inches or less - one half of one thousandth of an inch. This is
roughly 1/10th the thickness of a sheet of computer paper! The same engine
may be considered worn to its limit when this clearance increases to .0015
inches. Your automobile engine's crankshaft is entirely supported by these
types of bearings as well - and the tolerances are even finer.
If oil is lost even for a short time, serious metal-to-metal sliding contact
results in significant wear and possible destruction of one or both bearing
surfaces. Particles in dirty oil can get trapped and embedded, usually in
the softer outer bushing resulting in scoring and additional wear. It is
your responsibility to assure that your engine oil is maintained at the
proper level and changed regularly. Any warranty is not likely to cover
failure due to negligence.
Note that the valves, normal operated by a camshaft driven off of a small
gear on the crankshaft, are not drawn in their usual position for a common
small (side valve) engine to improve the superb clarity of these drawings.
This should bring up the schematic (diagram) of interest. I was really
surprised to find the diagrams - they appear to be quite useful and could
come in real handy in the future.
They have a great deal of useful information including diagrams of
popular carburetors, rope starter repair, and links to small engine
manufacturers. There is even a "slide-show" illustrating complete
disassembly of a typical small engine. This may be all you need for
many popular engines.
The following are good for general information but may not have the specific
information for your equipment. However, the combination of the original
user or service manual and a small engine repair book is probably all you
need.
(There are also several other versions of this book covering small engines
up to 20 HP. For the most part they are very similar with some additional
information provided where appropriate for each size range.)
(From: Jim Nelson (jgn@ameritech.net).)
This is an excellent book about B&S engines.
I don't know any old galoots who can teach me this stuff, so I always end
up at the bookstore. This book I had to buy to identify the missing
controls on a B&S driving a mortar mixer I bought cheap.
From the charter:
Check out: Yahoo Groups:
Small Engines Discussion Group.
Many engine parts are fairly specialized and non-interchangeable unless the
replacement part really is identical. However, even different model engines
may use the same parts. For example, the identical connecting rod, piston,
piston pin, camgear/camshaft and oil pump, valves, valve lifters, ignition
components, and flywheels are used in several different 3-5 HP Tecumseh
engines. Even the same crankshaft may be used in multiple models but slight
variations like whether there is an auxiliary power take-off or not can
complicate matters.
Carburetors, magnetos and other ignition components from similar sized engines
from the same manufacturer may be substituted in many cases. I have even
heard of people adapting a larger carburetor to a small engine (with varying
levels of success).
Here are some of the alternatives for obtaining replacement parts:
Sears is, of course, where you get Craftsman tools which in the past have
been of very high quality. All hand tools also come with an unconditional
lifetime warranty.
Sears now has a Web site: Sears
PartsDirect which allows direct ordering of over 4 million parts (so
they claim) based on the parts list (which they provide on-line) for each
product model number.
Parts availability is guaranteed for something like 15 years for most Sears
brand equipment. Since the Tecumseh engine design has really not changed
substantially for a lot longer than this, parts will likely be available
even for an old mower. However, the person at the parts counter may look
at you as if you are from Mars if you are interested in some of the very
low level engine replacement parts like circlips or rod bolts. It would
appear that not many people do this sort of stuff anymore.
For Sears/Craftsman products in particular, the first 3 digits of the Sears
part number identify the actual manufacturer of the equipment. With these
in-hand, you may be able to bypass Sears entirely and buy parts directly
There are a large number of parts supply companies. Only a few are listed
below. (I have absolutely no affiliation with any of the following companies.
Some of the descriptions are from the company's site or what they emailed me.
Listed in alphabetical order, more-or-less.)
The site has an on-line catalog (under construction) and search capability.
A free 200 page print catalog may be requested as well. (I have been
informed that they are currently out of these (May '97) but you will be put
on their mailing list for a summer release.) They also have a 600+ page
catalog (major portions of which will be put on their web site in the near
future) with all sorts of fabulous replacement parts, tools, and other
maintenance items - for the princely sum of $3.
- Web: M & D Mower Repair: http://www.M-and-D.com/
Orders are accepted via secure email, Fax or snail mail. Payment may be
made using MasterCard, Visa, or Discover. The minimum S&H fee is around $4.
Yard equipment dealers may take old (non-working) mowers as trade-ins and be
happy to sell or give away the remains for parts. Of course, if all you need
is a bolt, you will have to dispose of the rest of the carcass!
(From: BELJAN E (lvpy67c@ix.netcom.com).)
At the end of the season they say "never again" and move to an apartment or
hire a landscaper.
I paid $35 for a Sears Craftsman mower in perfect condition (I guess grass
mowing was not something the seller enjoyed) about 17 years ago and it is
still going strong with only minimal maintenance.
Garage and yard sales, tag sales, flea markets, and auctions, are also
excellent sources for tools. Very high quality tools often show up at
reasonable prices but there is a lot of junk out there so know what you
want and how to distinguish an easily salvageable tool from one that is
a pile of congealed rust.
(From: Mark Manville (manville@vega15.cs.wisc.edu).)
What I did when we bought our first house was to just go around to garage
sales and look for an inexpensive used mower. I figured I would need to cut
the lawn for a while before I was really sure of what I needed anyway.
Besides, after the down payment, closing costs, and other expenses, there was
not much free cash to speak of. Such a mower could perhaps take you through
the first year or so, until you have more experience, time, and cash. You may
even get lucky like I think we did and get one that you can stick with for a
while. We got a 22" Sears self propelled that works pretty well - it's
old, but at $30 I count it as a bargain, even if breaks down after one year."
(From: Erik Beljan (lvpy67c@ix.netcom.com).)
I would like to comment on buying used lawn mowers. Do not trust what you are
buying. You never know what the quality of the engine is and there is no way
to guarantee it. I found a Roper Rally 22 inch lawn mower last fall, and had
an interesting ordeal which shows what you might be getting. I took it home
only to find the engine was seized (found by attempting to pull the starter
cord). I took the sparkplug out and put a mixture of Duralube All Purpose
Spray, Marvel Mystery Oil, and Liquid Wrench into the cylinder. I put the
spark plug in and let it sit a few minutes. I took the plug out and yanked
the blade from the underneath. It snapped free. I then cranked it about 10
times, to clear the cylinder (if fouled the old plug that was in the mower) I
cleaned the plug off with some carb and choke cleaner, sprayed some into the
cylinder and carb. I proceeded to start it again. It kicked to life with a
huge cloud of smoke. It blew smoke everywhere for about 5 minutes. I shut it
off and parked it under a tree overnight so I could take a closer look the
next day.
The next day I took a better look at it only to find that the top of the
flywheel was full of poplar tree cotton, which I removed. I looked at the oil
which was a dark thick black color. I poured a large dose of Marvel Mystery
Oil into the oil and started the mower. I ran it for a few minutes (it burned
considerable oil), shut it off and changed the oil. I dumped the old oil out
and filled it with a 50 50 blend of SAE 30 oil and Nu Lube oil stabilizer (a
thickish oil treatment like STP thins out more though). I filled the gas tank
and put about 4 oz of Marvel Mystery Oil in the gas. I started it and ran it
for 10 minutes. No smoke, sounds like new. I am using it now this spring
with the only modification of a new spark plug and air filter. The thing runs
fine, but it is likely that the engine is in terrible shape internally (I am
not bothering to take it apart, but can it can be seen by the excessive oil
burning if I don't put some Nu Lube in the oil).
If I sold it to you today without telling you what I did to it, you would
never know, there are no outward signs of what it was like. The Nu Lube seals
the clearances nicely, stops the oil from burning, keeps the spark plug from
oil fouling, keeps the oil looking clean and quiets the engine quite a bit.
If I were the purchasing party I would not want to receive this engine if I
would have known its condition. This story goes to show that for minimal work
you can make an engine run in so it seems to be in decent shape, even though
it might not be.
The following are just samples - check
your engine manual for exact values!!! The most critical are the connecting
rod bolts or nuts and the cylinder head bolts.
-- end V2.38 --
All Rights Reserved
2. There is no charge except to cover the costs of copying.
DISCLAIMER
Improper use, testing, or repair of gasoline powered equipment can result in
explosion, fire, injuries including loss of limbs or worse, as well as total
destruction of your spouse's prized flower bed.
Introduction
Can you see above the weeds?
This document addresses some of the most common ailments and provides detailed
instructions for their diagnosis and cure. In addition, it provides detailed
maintenance guidelines to prolong the life and happiness of your lawn mower(s)
and other yard equipment.
SAFETY
Despite all the dire warnings (don't forget that the lawyers need to make
a living!) it is possible to use, store, maintain, and repair gasoline
powered equipment safely. Mostly, the necessary precautions are just
common sense - for example, don't smoke around gasoline (well, don't
smoke at all but that is not a part of the charter of this document!).
Tools and supplies
While you probably did not purchase your lawn mower specifically for the joys
of repairing it, there is always a chance that despite all your precautions,
the blade will strike a rock that just happened to grow out of the ground when
you weren't looking. Therefore, it makes sense to be prepared.
Lawn Mower Basics and General Maintenance
Gas, electric, or manual?
Many people who have never used a gasoline engine powered piece of yard
equipment are intimidated by all the warnings with respect to the explosive
nature of gasoline. They then opt for an electric lawn mower instead of
gas. For many, this is the correct choice. There are a different set of
precautions to follow but they are fewer and seemingly less of a threat.
Types of lawn mowers
Depending on the size of your lot, glowing conditions, and your energy
level, one or more of the following options will fit you like a glove:
The first two of these are described in more detail is subsequent sections
of this document. For the last, well you should already know if that
is appropriate for your life-style!
Reel mowers
These may be manual or engine powered. A spinning set of sharp spiral cutting
blades working against a fixed 'bedknife' snips off grass like a scissors.
In principle, reel mowers can produce an exceptionally consistent manicured
lawn. However, small reel mowers may have serious cutting height limitations
and also result in a wavy uneven appearance.
Rotary mowers
These may be gasoline or electric (AC line or battery) powered. A spinning
blade or blades whirls at the selected cutting height and lops off the tops
of you grass by side impact. This is most definitely brutal treatment of
your poor defenseless grass! The length of the cutting blade determines
how much of a swath is cut on each pass - typically 18 to 24 inches for a
walk-behind mower; up to 36 inches or more for a riding mower. Mowers with
large swath widths may use two or more smaller blades instead.
Dead-man control
All rotary mowers manufactured within the past 15 years or so must have
a dead-man control to stop the blade quickly (within a couple of seconds)
if the handle is released or the operator falls off of the seat of a riding
mower or lawn tractor. While not foolproof, this feature greatly reduces
the chances of serious injuries due to accidental slipping or falling - or
attempting to make adjustments while the blade is spinning.
Always restore the dead-man control to normal operation before attempting
to start the mower.
Types of rotary mowers
In addition to options with respect to gasoline or electric power, rotary
mowers can be classified based on such things as: walk-behind vs. ride-on,
to bag or not to bag, and rear or side discharge or mulcher:
Putting a mower into service for the first time
If this is a new purchase, you should have a users manual - READ IT!!!
Gasoline
Use only fresh unleaded gas. Regular octane rating (87) is fine - small
engines operate at relatively low compression ratios so knocking should
not be a problem. There is likely no benefit to using anything higher.
In fact, I've heard that small engines may actually be harder to start and
run poorly on expensive high octane gas due to their low compression ratio.
Gas that is over a month old may have lost some of its more volatile
fractions resulting in hard starting, possible varnish formation, and other
undesirable effects. At the end of the season, dump the unused unmixed
gas into your car (preferably when its fuel tank is at least half full
so your old gas gets mixed with fresh gas). This way you won't be tempted
to use it at the start of the next season.
Where to buy gasoline
Your nearest auto service station will sell you small quantities of gasoline.
As noted in the section: SAFETY, you must use an approved
gasoline safety can which will be red in color. These come in sizes from 1 to
5 gallons or more and may be made of plastic or metal. A convenient size is 2
to 2-1/2 gallons. The fuel tank on a typical walk-behind mower will be
between 1/4 and 1/2 gallon.
Where to fill gas can
Always remove the gas can from vehicle before filling it. In addition to
common sense 'what ifs' with respect to spills and fume buildup, there may
be an added risk of the buildup of static electricity:
Gasoline additives or stabilizers?
The use of a proper stabilizer can often substitute for the task of draining
the gas between seasons by preventing the formation of insoluble gum that
would otherwise eventually clog up your carburetor.
"Isn't there a gasoline additive you can add to the gas which will keep it
'fresh' for up to 24 months? I've seen it at Home Depot, though have never
used it. I think a tube was less than $1.00."
Before you start mowing
Note: while written with gasoline powered rotary mowers in mind, most of
these comments apply to electric models as well.
Starting the mower
Most mowers and other small pieces of gas powered yard equipment use a self
retracting recoil type starter. You pull on a handle attached to a cord wound
around a one-way clutch affair. Pulling on it rotates the engine's crankshaft
and the clutch allows the engine to run without pulling you back into the
mower! If yours has an electric starter, then you don't need to tug on
anything - plug it in and push a button or turn a key. Of course, finding
an outlet at the far end of a large yard may prove to be a challenge. With
larger equipment like riding mowers, power is usually provided by an on-board
rechargeable battery. In either case, there will be some kind of backup
recoil or rope starter should the electric start be unusable or inconvenient.
A primer on priming
Many small engines have replaced the choke with a primer - a rubber bulb or
button that is supposed to be pushed several times before attempting to start
the engine. Under the right conditions, this is a very effective approach.
However, here are a couple of things to keep in mind:
Stopping the engine
On most inexpensive lawn mowers manufactured within the last 10 or 15 years,
releasing a dead-man bar on the handle both kills the engine and applies
a brake to the blade (well, actually the flywheel of the engine). In this
case, there is nothing to think about - just release the handle and it
will stop within a second or two. These are quite reliable. The usual
problem is that you forget to engage the dead-man bar and attempt to start
the mower despite the basic fact that this is quite impossible!
Suppose it fails to stop?
What should you do if the engine stop switch has no effect? Probably the
safest and surest is to use a wooden stick to pop the spark plug connector
off of the spark plug terminal. This **will** stop the engine.
Maintenance Guide
General preventive maintenance
Here is what you should do at the end of the mowing season:
Checking the oil
The following applies only to 4 stroke engines. For 2 stroke engines, special
oil must be mixed in proper proportion with the gasoline.
About engine oil
For the common 4 stroke engines such as Briggs & Stratton or Tecumseh,
you don't need to buy specially high priced engine oil. The type likely
used in your automobile will work fine and will be much less expensive.
Although small engine manufacturers may recommend SAE 30 oil, they usually
also state that 10W-30 or 10W-40 are acceptable substitutes - and these
are what your car probably uses. New oil should have at least the SG
rating though if you have some SF in your garage, that will be fine also
(for your lawn mower, not your car!). However, there are situations like
equipment that must run in extremely cold weather (probably not a problem
with grass mowing!) where specific alternative oil recommendations should
be followed.
Oil change
If you don't do anything else to prolong the life and happiness of your
small engines (and your automobile, for that matter) it should be an
oil change at the recommended interval. Oil loses its lubrication and
cooling effectiveness with use and this will gradually take its toll on
your precision engine parts. Even a simple lawn mower engine is machined
to very precise tolerances and any contamination will increase wear.
Ultimately, its performance - starting and running - will suffer and its
life will be shortened.
An oil change isn't really a big deal
The oil change procedure is a lot simpler than for an automobile as
everything is readily accessible and there is no oil filter to worry about.
Blade sharpening
The blade in a rotary lawn mower doesn't need to be sharp as a carving
knife or scalpel but serious dents and nicks will result in a less than
perfect lawn (to say the least!). In addition, a seriously unbalanced
blade can result in excessive vibration and eventually, possible internal
damage as well.
Non-violent blade removal
For just some minor touch up, there is no real need to remove the blade. For
major grinding and balancing, removal will be needed. Removal will also be
required to inspect for a damaged or sheared blade lock key and to replace
it if necessary.
"I'd wish I'd read this a few years ago. I used an open-end wrench and it
'flexed' off of the bolt. Needless to say, my next week wasn't a lot of fun
with 10 stitches in my hand."
Carburetor adjustments
If your engine is relatively new (made within the last 10 years or so) and
has only one speed, then there may be no adjustments (like the one discussed
in the section: Cleaning Craftsman (Tecumseh)
carburetors. It will either work or it won't - in which case it needs
cleaning or parts replaced. Or your overhaul was less than 100% effective.
You can tell if your carburetor is of this type as there will be no adjusting
screws on the carburetor. For Craftsman types, there will be a solid hex nut
on the bottom holding the float bowl in place. There may or may not be a
primer button.
Notes on Briggs & Stratton tune-up
(This assumes foam type air filter that needs have a film of engine oil in it
to trap dust.)
Setting engine speed
Many inexpensive mowers don't even have a speed adjustment screw. Spring
tension and the linkage to the governor set speed - period. Note that actual
speed is rarely that critical for engine driven equipment as long as it is
within safe limits. See the comments below on string trimmer speed settings.
However, what options do you have where there is a need to set the precise
engine speed?
Adjusting the carburetor on a 2 stroke engine
This is generic advice but probably a good place to start. It assumes that
there are 2 adjusting screws - idle and high speed mixture.
Troubleshooting Guide
Instant troubleshooting chart - most common problems and possible causes
The following chart lists a variety of common problems and nearly all possible
causes. Diagnostic procedures will then be needed to determine which actually
apply. The 'possible causes' are listed in *approximate* order of likelihood.
Most of these problems are covered in more detail elsewhere in this document.
Possible causes:
Possible causes:
Possible causes:
Possible causes:
Possible causes:
Possible causes:
Possible causes:
Possible causes:
Possible causes:
Possible causes:
Possible causes:
Lawn mower will not start
This is probably the most common problem you are likely to encounter.
The cause is very often the same - lack of maintenance.
Lawn mower is hard to start
Most of the time, the possible causes and solutions will be similar to
those where the engine doesn't start at all. So, see the following sections
for more information. However, here are some specific issues dealing with
engines that do start eventually and then run fine:
Determining why it won't start
Think: FAST - Fuel, Air, Spark, Timing. Diagnosing a balky engine is
not difficult but a step-by-step methodical procedure will make it a
lot less traumatic. Despite all the warnings, serious problems rarely
develop on their own. Most likely, there is a simple, easily remedied
cause.
Fuel
Obviously, the engine won't run without gas!
Air
The optimal air:fuel ratio is around 14:1. This must be lower for a cold
engine and thus a choke plate or other means to increase the richness of the
mixture is usually provided. A choke plate restricts air intake forcing
more gas to be sucked into the cylinder. A primer bulb effectively squirts
gas into the intake pipe to augment the normal carburetor action. Some
carburetors have no choke and no primer but incorporate a small gas reservoir
which fills when the engine is off and provides some extra when starting.
Spark
All common lawn mower engines require a precisely timed spark to ignite
the air-fuel mixture in the cylinder. The existence of a spark can easily
be tested as follows:
Lack of spark
If your mower is less than 15 years old, there is an excellent chance that
if uses an electronic ignition system. These are very reliable as there
are no points or condenser to go bad and no need for routine tune-ups.
Checking the spark plug
Use the proper socket to remove the spark plug and inspect it for damage and
general appearance:
Testing the magneto
The magneto, like the ignition coil on an automobile, contains two windings:
Timing
For power to be developed, the ignition of the compressed air/fuel mixture
must take place at exactly the correct instant - just before the piston
reaches Top Dead Center (TDC) on the compression stroke. With automotive
engines, there are mechanisms to advance the spark at higher revs but
simple lawn mower engines do not have this complication, at least.
Lawn mower will not start after the blade hit an obstruction
The following description applies to most small rotary lawn mowers with
direct driven blades. The vast majority of these use either Tecumseh (as
found a variety of Sears/Craftsman equipment) or Briggs & Stratton engines.
However, similar comments apply to others as well including Lawnboy two
stroke engines and the more modern Honda and other overhead valve type of
engines.
Flywheel removal
Remove the shroud (blower cover) if you have not done so already. This is
usually fastened with 4 screws and hopefully does not involve any head
bolts - if so, you will need to tighten them to the proper torque using a
torque wrench once you have remedied the problem. You may need to remove
the fuel tank (if you have not done this already) and other trim pieces as
well.
___ ___
|___| |___|<-------- Self tapping bolts or pretap holes.
| | | |
_|-|_ _|-|_
| |-| | | |-| |<------- Tighten nuts to release flywheel.
___|_|-|_|__________|_|-|_|___
| |-| |-| |<--- Plate or block - 1/4" or thicker steel
|_____|-|______________|-|_____|
|-| .-.----.-. |-|
|-| | :----: |<-|-|---------- Flywheel nut - loosen slightly.
|-| |_:----:_| |-|
______|-|___ :----: ___|-|______
//////:-:///|:----:|///:-://////
//////:-:///|:----:|///:-:////// <-- Flywheel comes with predrilled holes.
//////'-'///|:----:|///'-'////// (taper not shown - ASCII limitations!)
//////| |///|:----:|///| |//////
Flywheel removal on Briggs & Stratton engines
The following applies to most B&S engines with the square starter shaft. This
procedure will be needed to gain access to the points and condenser (on
engines without electronic ignition), oil seal, etc.
Flywheel inspection
Once the flywheel is off, inspect the keyway on the crankshaft and flywheel
for damage. Serious damage will require replacement of the affected parts.
Slight burrs can be removed with a small file. If there are any cracks in
the flywheel radiating from the hole, the flywheel MUST be replaced as this
is a serious safety risk - the flywheel could literally explode when run
at full speed. However, don't be concerned by surface flash - lines that
look like fine cracks resulting from the molding process. To confirm
that these are not cracks, there will be no visible penetration inside the
shaft hole and fine sanding will quickly remove all traces of this flash.
Why soft metal keys must be used
Normally, the soft metal keys lock the blade and flywheel to the crankshaft.
However, should the blade strike an obstacle and stop suddenly, one or both
key(s) will shear and reduce the likelihood that the very expensive crankshaft
or other parts will be damaged. The reason is that the substantial inertia of
the crankshaft and that of the flywheel will tend to try to keep them rotating.
Something has to give and you want it to be the 25 cent key and not the $75
crankshaft! However, this isn't foolproof as explained in the section:
Why you really don't want to attempt to move an immovable
object.
Engine dies or won't restart when hot
(From: Wild Bill (kwag98@tcis.net).)
Smoke signals
For the most part, smoking is just as bad for a small engine as it is for
you. Excessive smoke from the engine may be an indication of problems
with the carburetor, rings, or gasoline:
Lawn mower smoking after oil change
(From: Wild Bill (kwag98@tcis.net).)
About squeals and other animal noises
While some may describe the engine of an antique automobile as 'purring', this
will not likely apply to most gasoline powered lawn mowers. It would seem
that noise reduction is just not a high priority design issue with lawn mower
engineers or marketing types. However, even if not exactly quiet, the sound
made by a healthy mower should not be similar to that of a pig being tortured.
Lawn mower fuel tank leaking
Fuel tanks can leak for a variety of reasons including defects in
manufacturing, abuse, corrosion, etc. However, before you buy a new tank,
a couple of notes:
Lawn mower too loud
Small engines - especially those on cheaper mowers - are usually loud, no
question about it. However, if yours sounds like it is about to explode or
take off, there may be something actually wrong.
Lawn mower wheels
Wheels tend to get banged about and damaged or may just become loose and
unstable due to wear. Wheels and wheel bolts are readily available at
home centers (or Sears for Craftsman mowers).
Intermediate Level Maintenance and Repair
Cleaning Craftsman (Tecumseh) carburetors
Simple float carburetors are found on a variety of equipment including many
engines made for Sears by Tecumseh. The basic procedures applies to the
float carburetors of other manufacturers as well.
Carburetor removal
Disassembly
Most carburetors on Craftsman mowers are variations on a common float design.
Newer mowers tend to have no adjustments and no choke - which greatly
simplifies cleaning and adjustment. With respect to adjustment, there is
none - it either works or it doesn't. If it doesn't, your cleaning was
not thorough enough, some parts need replacement, or the problem is not
in the carburetor.
Cleaning the carburetor parts
Use carburetor cleaner and lint free cloths or paper towels to remove all
built up brown or green gunk, varnish, and other contamination from the
metallic parts. Pay particular attention to the machined passages and
metering holes.
_ _
| | | |
| | | |
| | |_|
| | _ Hole in nut (approximately .025") - use carburetor cleaner
| | | | and wooden toothpicks to clear it out down to shiny brass.
| | | | DO NOT use metal wires!
_| | _ | |_
| \_/ |
|___________|
Critical considerations for proper operation
Reassembly
Once all parts have been cleaned and inspected - replaced where needed,
proceed as follows:
Carburetor installation
With the carburetor positioned in its approximate location on the engine:
Throttle/speed control linkages on Craftsman/Tecumseh engines
The following is for one model! NOT ALL ENGINES ARE SET UP THE SAME! It is
best to consult your engine manual. Getting it wrong is not something you
really want to do! :(
__ _
Open <-- / \ --> Close | |
|o=========. ,=======o| Top hole
\ O / '=============' | |
\_/ Carburetor +-- ===========o| Next hole
_ Throttle | | |
|o| Plate +-straight-+ | |
| | | | |
|o=====o---/\/\/\/\/\/o========== ---+ | |
| | Spring | |
| O | | |
Speed Control | |
or Fixed Tang Governor |_|
(linkages may cross) Lever | O |
+---+
Initial tests
Add a small amount of gas to the fuel tank - perhaps half a glass or so.
Just enough to assure that it will reach the carburetor even if the mower
is slightly tilted or jostled.
Maintenance of point-type ignition systems
In most cases, missing or total lack of spark will be due to dirt, pitting,
or corrosion of the points or a failure of the condenser. Timing may
affected as well by excessive wear. The following procedures should restore
the ignition system to good health:
Setting the point gap and ignition timing
Perform the following whenever the breaker points assembly is replaced or
where a timing problem is suspected.
Recoil (pull) starter repair
Broken lawn mower handle
Should the tubular handle on your mower break at some point (yes, I know this
should be unlikely but I know of two people who have managed to do it!), the
use of a splint is probably the best approach. Obtain a length of steel pipe
with an inside diameter just a hair larger than the outside diameter of the
handle. About 8 to 12 inches should be enough. Even electrical conduit may
work. Use this to splice the joint. Drill holes through both the pipe and
handle and secure with sheet metal screws. This will maintain the required
strength and keep the handle the same length as it was originally so you
will not have to become a midget to mow your lawn.
Diaphragm carburetor problems
"I Recently inherited a BobCat Snow Blower from the 60's or 70's. It has
a Lausen 3.5hp (HR35P-2403P). I just installed a Tecumseh Rebuild
Kit#631893. The unit runs way too rich, I run out of gas in 10 minutes,
the muffler starts to glow red. I cannot get it to idle. I installed a
new needle, seat/jet and diaphragm. During the rebuild I did not remove
the welch plugs. I tried swapping the idle screw with the high speed
screw (not sure which is which). One screw has a smooth taper while the
other has a taper with a step to it (no evidence of scoring). Could I be
missing a key piece that regulated fuel flow? The rebuild kit did not
come with directions, so I just installed everything in reverse."
Metal gas tank repair
Yes, you have to remove the gasoline first! And, make sure all traces of
vapors are gone - if it smells like gas, it may very well explode! However,
this isn't as much of a problem as with an automotive gas tank.
Engine Overhaul
When does this information apply?
This chapter deals with the following:
Do you need an overhaul?
Many common problems can be remedied without going into the deep dark
recesses of the engine. However, some will require either a partial or
total overhaul. Eliminate all other possibilities from consideration
before considering an overhaul - it will not be a fun afternoon (or
weekend, or week, or month,....).
Comments on engine rebuilding
While the specific question dealt with a medium size snowblower engine, the
comments should apply to other yard equipment as well.
"Is it economical or feasible to properly rebuild a 7 HP Tecumseh engine on a
snowblower? Compression seems fine. Has been burning oil to some degree for
the last 3yrs, but this year its' burning a lot - maybe 1/2 pint oil for each
gal of gas. Until last year, was using 5W30. This year, switched to straight
SAE30. I could get a new Tecumseh SnoKing engine for about $350 including
shipping."
Compression testing
Special compression gauges are available at auto parts stores or small
engine parts suppliers. These will catch and hold the highest pressure
reached so you don't need to be in two places at once.
Should you even bother?
Only you can decide if the time and effort will be worth it. If you enjoy
a challenge, then engine overhaul may be for you. However, this is probably
not going to be your idea of fun. Doing something like this for the first
time *will* result in scraped knuckles and the liberal use of 4 letter
expletives. If the mower was a Hechinger's $100 special and has seen
several seasons of use, then it may be time for a new one.
Special tools
For most of the procedures described below, the basic set of items listed
in the section: Tools and supplies will suffice.
However, some of the following more specialized tools may be needed depending
on how far you go:
Prepare your work area
Once the gasoline and oil is drained, all overhaul work can be done indoors.
Without gas, there is little risk and working indoors is generally much more
convenient. Therefore, you need to decide where to set up for the overhaul.
The best location will be relatively dust free, well lit, and not likely to
be required for other purposes. Your engine may be remain in a disassembled
state for some time if you need to obtain replacement parts. Also, even with
its bodily fluids removed, an old engine will stink. Therefore, the dining
room table is probably not the ideal choice!
Engine overhaul procedure
The following description applies directly to a large number of Craftsman
mowers using Tecumseh engines (most do). However, with minor modifications,
it is also applicable to most other mowers using 4 stroke engines.
Prepare the engine for removal
While for certain repairs it is quite possible to work on the engine while
still mounted on the mower or other yard equipment, it will almost always
be much more convenient to disconnect and remove the entire engine to the
convenience of your workbench. There are generally only a handful of actual
connections. A typical small engine is remarkably light and compact once
stripped of the mower deck!
Remove the engine
At this point, the engine should be free of all its attachments to the
mower except for its mounting. For a typical rotary mower, there will be
three large bolts accessible from under the deck. Removing these with the
proper socket will allow the engine to be lifted and moved to your workbench.
You will probably be surprised at how light it is! I recommend just
screwing the bolts back into their threaded holes finger tight. That way
they will not get lost and the threads will be protected. Also, Protect the
threaded end of the crankshaft with a bit of rag or paper towel fastened
with an elastic band.
Engine disassembly
The following sections provide the detailed procedures for disassembly
and initial inspection for major damage. As noted, these apply directly
to most Tecumseh engines but most other 4 stroke engines are very similar.
Removal of the accessories
Now it is time to get down to business! As noted, depending on your situation,
not every step will be needed.
Carburetor
Muffler
Note that in addition to decreasing the noise from your engine, the muffler
serves a very important spark/flame arresting function. Therefore, it
is important that it be in good condition.
Flywheel
Ignition
This can be left in place but will be susceptible to damage.
Cylinder head
Valves
You should only need to do this if you are replacing or grinding a valve.
In most cases, the valves are undamaged but may appear in poor condition
due to carbon buildup - which can be removed in-place fairly easily.
Oil sump/crankcase cover
We are now going into the lower section. I can hear you saying "Joy!".
Camshaft/camgear
Connecting rod
Piston
Crankshaft
Breather
Oil seals
Detailed inspection
A complete overhaul can restore a small engine to like-new condition. Any
parts that are found to be damaged or out of tolerance are repaired or
replaced.
Engine reassembly
Once you have performed whatever magic is required to repair or replace
broken or damaged parts, here are the steps that will transform your pile
of parts into a (hopefully) working engine.
For the following steps, position the engine on wooden blocks blade/PTO side
down.
The camgear timing mark (if not marked) is in line with the center of the
hobbing hole (small hole in the face of the gear).
Flywheel/magneto end
___________________
/| | | | | | | | 8 |
|5| | | |3| | | |=|=O |
| O=|=|=|=O=|=| | | | |
/| | | | | | | | _ | |
|1| | | | | | | | |O| |2|__
| O | | | | Spark Plug O |
| | | | | | | | | | | | | |
\|7| | | |4| | | | | | | |
| O=|=|=|=O=|=| | |6| | |
/\| | | | | | | |=|=O |__|
___/____\|_|_|_|_|_|_|_|_|_|___\___
-----------------------------------
PTO/Blade end
Engine installation
It will be easier to tighten the flywheel nut to the recommended torque
once the engine has been reinstalled on the mower. Therefore, now is a
good time to install the engine to the mower deck:
Initial post-overhaul testing
Assuming you didn't make any mistakes, the engine should start on the
first pull. As you start it, look and listen for any abnormalities and
immediately stop it if any are detected:
Items of Interest
Explosion risk when filling a metal gas can
Although rare, there have been reports of fires resulting during fuel
transfer. Simple precautions can minimize this risk.
Why you really don't want to attempt to move an immovable object
The rotating blades and mass of the internal engine parts pack quite a
punch. Speeding along merrily mowing away one doesn't think about this.
However, if the blade should hit an obstruction, you may have no choice.
Blade tip /
hits curb. X-------____________________________________
Ouch! / | | Inertia of this
/ | - O - | | side of blade
/ |____________________________________ | | attempts to
| | | | ------- | continue in same
V v v v v v v direction.
Net sideways force
on crankshaft
How about a crankshaft friendly blade?
It is too bad that most lawn mower blades are made of heavy rigid steel
(though I do recall a mower that used a super thick nylon cord - sort of
like a weed whacker on steroids). The chance of serious engine damage
from curb kissing would be greatly reduced if a blade were used which had
less inertia and increased flexibility. Then, no matter how hard you tried
to whack something solid, only the blade lock and/or flywheel keys would
shear and thus spare the expensive engine parts.
"I use a top notch Supa-Swift with a gravity cast alloy chassis and swing-tip
blades (Australian invention, no bent cranks on our mowers mate!)"
Crankshaft-friendly blade sighted
(From: Thomas Prufer (Prufer@compuserve.com).)
Another reason not to mow rocks!
(From: Forbes Family (fbsfam@clear.net.nz).)
Rod disasters - or why the oil and governor are kind of important
A combination of low oil (well, actually, almost no oil) and probably too
high RPMs resulted catastrophic failure of the connecting rod and cap on
my garage sale Eager 1 Craftsman mower. I had just completed cleaning
the carburetor and was testing it when p-ting!! and it stopped dead - the
rod had broken and it was dead-dead. Extremely embarrassing since there
was no excuse for such a disaster.
I forgot the oil and now it's stuck
OK, so you didn't read this document first or just got distracted while
changing the oil and you ran the thing with no oil until it came to a
screeching halt. Assuming nothing actually broke - it just won't turn at
all, there may still be hope without a complete refurb (which in reality
probably means a new mower):
So you got oil in the cylinder
"I tilted my Toro to work on it and now can't start it because oil flooded
into the cylinder. I already cleaned up the plug. Is there anything I can
do to clean out the oil without taking the engine apart?"
So you put gasoline in the oil filler hole
Don't panic, just get it out of there. Drain the oil/gas mixture completely
and refill with the proper new engine oil. If you want to be doubly sure, run
the engine for a minute or so to mix any of the remaining contaminated
oil with the new oil, then drain and refill again. It really shouldn't have
done any damage if you get it out of there reasonably quickly (I don't know
what effect gas might have on the oil seals over time though).
Oil starvation from mowing at too steep an angle?
4 stroke engines require oil to continuously coat the various moving parts
during operation. There are two types of systems used in most small engines:
splash lubrication and forced oil lubrication.
Additional comments on winterizing - draining versus the use of fuel a stabilizer
Not everyone agrees with the recommendation to drain the fuel at the end
of the season as described in the section: General
preventive maintenance.
Testing a used lawn mower before you buy
A used mower at a bargain price may not turn out to be such a bargain if you
have to do extensive repairs. There are two types: the living and the dead.
Discussion of 2 stroke engine rebuilding
"I am in the process of refurbishing an old Eska 7.5 H.P. outboard boat motor.
The engine (a 2-stroke Tecumseh) runs fine when under load at full throttle.
Does your 2 stroke engine use reed valves?
Since a bad reed valve can be the cause of a variety of problems, knowing if
you even have these can be useful - not all 2 stroke engines use reed valves.
Some problems with Briggs and Stratton engines
(From: Mike Brandt (mwbran1@uswest.com).)
Comments on Briggs and Stratton repair
The following was in response to a posting on alt.home.repair about a 12 year
old lawn mower. Of course, if properly maintained, such an engine may still
have quite a bit of life left in it :-).
Experience with Briggs & Stratton carburetor
(From: Dan Hicks (danhicks@millcomm.com).)
McCulloch chain saw hard to start
"This weekend I picked up a 14" McCulloch chain saw and have had a hell of a
time getting it started. I am no novice at this as I already have a gas
trimmer and blower. I am sure my fuel mixture is right and have done just
about everything else by the book. In how many pulls do I consistently start
a cold McCulloch chain saw. I should mention that I HAVE started it but can't
believe it should be this hard."
Riding mower stops periodically
(From: Mike Odryna (modryna@ix.netcom.com).)
How do you get the blade off a tractor mower?
(From: Lloyd E. Sponenburgh (lloyds@fiscalinfo.com).)
About Wico magnetos
These are separate units (not part of the flywheel assembly) and may be found
on larger (usually horizontal crank) engines.
What is inside a small engine electronic ignition module?
The advantage of these systems is that there is no maintenance as there are no
points to wear out or gum up. Timing is fixed by the relationship of the
flywheel magnet and sensor. There are also no adjustments except to set the
magneto coil pole piece to flywheel air gap.
Capacitor discharge ignitions systems
(From: Matthias Meerwein (mmerwei@eis.k8.rt.bosch.de).)
Which manufacturer makes what brand names?
The following could be retitled: Sales people don't have a clue of what they
are talking about most of the time or make something up to please the customer
(and pad their commissions). I'm not sure how much of the following can be
trusted though in all fairness, it may be that manufacturers switch around
like musical chairs. :)
Comment on modern manual mowers
(From: Peter Szymonik (Xorg@msn.com).)
Comments on electric mowers
(From: Leslie Gerstenfeld (lgerst1@umbc.edu).)
Comments on mulching mowers
(From: Jeff (kahlua53@aol.com).)Kahlua53
Comments on inexpensive lawn mowers
True or false?:
"Throw away mowers will always cost you more in the long run. Murrays and
MTDs are bargain basement mowers, and you most definitely get what you pay
for."
Comment on high wheeler and wish list
(From: Edward Rice (ehrice@his.com).)
Comments on plastic decks
(From: Joe Kowalski (builder@proaxis.com).)
Comments on Briggs & Stratton versus Tecumseh engines
These two manufacturers produce the vast majority of small engines used in
low to medium priced yard equipment.
Comments on trimmers
(From: Alan Dale (ASD43@webtv.net).)
Comments on Honda overhaul
(From: Israel Kantorowicz (kant@sqi.com).)
Walk behind versus riding mower or tractor
(From: Stephen M. Henning (shenning@fast.net).)
A lawn mower for the security minded
Smarter (and lower maintenance) than the average cow...
"This is a lawn mower that is solar powered and stays within a buried wire
boundary. It also 'learns' the layout of your yard and will even put itself
away at night. Does anyone have one of these devices? It sounds great, but
at $1,500, I would like some real world product feedback."
The miracles of JB Weld
OK, I have no idea of whether the following repair will actually hold up
but I supposed there is nothing to lose by trying:
Interesting lawn mower repairs
(From: Sean Smith (seansmith@racemark.com).)
Importance of having the correct valve clearance
Since would be hard to have valve-clearances of all engines here, look in
the owner's manual. Many manufacturers have them on-line. See the
section: Links to engine and equipment manufacturers.
A search engine (no pun...) will also find these quickly.
(From: Derrick Setchell (D.Setchell@eastman.ucl.ac.uk).)
Valve adjustment for OHV engines
(From: Mike's Small Engine (smallengineparts@yahoo.com).)
Internal Combustion Engines
Small engine technology
If you have some idea of how your automobile engine operates - or a Model T
Ford for that matter - then you know the basic operating principles of your
small engine as well. In fact, your Craftsman Eager 1 has a lot more in common
with a Model T than a Honda Accord. However, strip off, the electronics,
pollution control devices, and engine powered accessories, and the basic
mechanical construction is very similar, though the lawn mower engine is
not manufactured to quite the same tolerances and with the same quality
materials as an automobile engine.
Types of engines
Unless otherwise noted, most of the descriptions and procedures in this
document apply to both 4 stroke and 2 stroke engines. However, there are
fundamental differences in the proper fuel and oil that is used with each
type.
Parts of a 4 stroke engine
You may be surprised at the large number of individual parts which comprise
the engine even on a $100 mower. The following description is for a typical
single cylinder 4 stroke engine as would be found on most rotary mowers,
rototillers, shredders, backup electric generators, larger snow throwers and
leaf blowers, and even modest size riding mowers and lawn tractors:
Provides some or all of the inertia so the engine can coast through the
3 non-power strokes of the full cycle (4 stroke). However, with rotary
mowers in particular, the blade provides some of the inertia due to the
use of a lower mass (lighter, so this is not all bad!) flywheel.
Engine operating principles
These are internal combustion engines which means that the burning of the
fuel-air mixture itself powers the engine. External combustion engines use
the heat from combustion to expand or boil a working fluid as in a steam
engine. Other examples of internal combustion engines are the rotary
Wankel engine and gas turbines (jet engines).
Bearings and bushings
The shafts of rotating parts normally are mounted in such a way that friction
is minimized - to the extent needed for the application. A bearing is any such
joint with more specific terms used to describe the typical types found in
lawn mowers - or small motors, automobile engines, or 100 MW turbines.
Crankshaft anatomy
The diagram below shows the major parts of the crankshaft:
Counterbalance weights
__ | __
| | | | |
Threads for | |<-+->| | Threads for
Flywheel nut | | | | blade adapter nut
| | | | | __ |
V _________---| | | |-|__|_______ V
...---/ | | | | | |__| ----+...
||| | | | | | | |__| | ||||
'''---\_________| | | | | |__|_______----+'''
^ ---| |_____| |-|__| ^
| |--| |--| ^ |
Main bearing | | | | | Main bearing
(Flywheel end) | |_____| | | (PTO/blade end)
|__| ^ |__| |
| +--- Crank gear (meshes
with cam gear)
Crank pin
Journal
Basic operation of a float type carburetor
The diagram below shows a schematic of a typical float type carburetor with
the engine running at high speed. The choke plate is fully open and the
throttle plate is opened the proper amount be feedback from the governor
to maintain the speed set by the user throttle control.
Air filter (Air: -->, Air+fuel: ==>)
_____________
/ \ Choke plate Throttle plate
| ||||||||| | (Fully open) Venturi (Partially open)
| ||||||||| |______________ v _______________________________
| ||||||||| \______/
| ||||||||| -> -> -> -> -> ==> ==> / ==> Intake
| ||||||||| -> ----O---- ---> ===> ==> ==> O ==> pipe to
| -> -> -> -> -> __||__ ==> ==> / | ==> cylinder
\____________________ ___/ || \_____________|__________________
|| || |
Fuel __________ Air bleed ->|| ||<- Main nozzle o---------+
Inlet ______ |____________||______||__ |--> Pull
| |_ _| || \ Speed <--/\/\/--+ from
Needle ->| __A_______________ || | control Spring governor
Valve | |o__/ \ || | closes
|-----| Float |-----||---| throttle
| . . | | Gas || . |<- Float bowl plate
| . . .\_____________/. . . || . |
\______________________________/
The four strokes of a four stroke engine in living ASCII art
You will just love the most excellent, accurate, and to-scale (:-).)ASCII
renditions below but at least it will display on any computer using a fixed
width font and not require half your disk space allocation for storage!
Intake stroke (1)
Air-fuel mixture is sucked into the cylinder by the by piston moving down
driven by inertia of flywheel (and blade).
From ignition/magneto coil >========
||
||||
Spark Plug ||||
/||\
_________________________| || |________________________
| _______________________| || |______________________ |
| | ==" | |
| | ______ -> -> -> -> -> -> -> -> -> | |
| |__ \____/ ___ -> -> -> -> -> ___ ______ __| |
|____\ || / | _____________________ | \\____//____|
Air-fuel || | || || | ||
mixture from ---> || | ||=====================|| | ||
carburetor ______ || / ||=====================|| \ || ______
| ____||||___ ||=====================|| ___||||____ |
| | || | || | || | || | |
| | || | || Piston | O || | || | |
| | | || V \ || | || | |
| | | || _ _ _ _ _ \ _ _ _ || | | |
| | Intake | ||/ \ \|| | Exhaust | |
| | Valve | | \ | | Valve | |
| | Open | | \ | | Closed | |
| | | | Rod \ | | | |
| | | | \ | | | |
\
---> O Crank pin journal
/
/
/
O
Main bearings
Compression stroke (2)
Air-fuel mixture is compressed as piston rises in sealed volume of combustion
chamber driven by inertia of flywheel (and blade).
From ignition/magneto coil >========
||
||||
Spark Plug ||||
/||\
_________________________| || |________________________
| _______________________| || |______________________ |
| | ==" | |
| | ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ | |
| |__ ______ ___ | | | | | | | | | | | ___ ______ __| |
|____\\____// | _____________________ | \\____//____|
|| | || || | ||
|| | ||=====================|| | ||
______ || / ||=====================|| \ || ______
| ____||||___ ||=====================|| ___||||____ |
| | || | || ^ || | || | |
| | || | || Piston O | || | || | |
| | || | || / | || | || | |
| | | || _ _ _ / _ _ _ _ _ || | | |
| | Intake | ||/ / \|| | Exhaust | |
| | Valve | | / | | Valve | |
| | Closed | | / | | Closed | |
| | | | / Rod | | | |
| | | | / | | | |
/
Crank pin journal O
\
^ \
| \
O
Main bearings
Ignition
Compressed air-fuel mixture is ignited just before piston passes Top Dead
Center (TDC) and starts down again.
ZAP!
From ignition/magneto coil >========
||
||||
Spark Plug ||||
/||\
_________________________| || |________________________
| _______________________| || |______________________ |
| | ==" | |
| | - X - | |
| |__ ______ ___ _____________________ ___ ______ __| |
|____\\____// || || \\____//____|
|| | ||=====================|| | ||
|| | ||=====================|| | ||
______ || / ||=====================|| \ || ______
| ____||||___ || || ___||||____ |
| | || | || Piston O || | || | |
| | || | || | || | || | |
| | || | || _ _ _ _ | _ _ _ _ || | || | |
| | | ||/ | \|| | | |
| | Intake | | | | | Exhaust | |
| | Valve | | Rod | | | Valve | |
| | Closed | | | | | Closed | |
| | | | | | | | |
---> O
| Crank pin journal
|
|
|
O
Main bearings
Power stroke (3)
Heated expanding gases drive piston downward and apply power impulse to
crankshaft via connecting rod (clockwise rotation).
From ignition/magneto coil >========
||
||||
Spark Plug ||||
/||\
_________________________| || |________________________
| _______________________| || |______________________ |
| | ==" | |
| | | | | | | | | | | | | | |
| |__ ______ ___ V V V V V V V V V V V ___ ______ __| |
|____\\____// | _____________________ | \\____//____|
|| | || || | ||
|| | ||=====================|| | ||
______ || / ||=====================|| \ || ______
| ____||||___ ||=====================|| ___||||____ |
| | || | || | || | || | |
| | || | || Piston | O || | || | |
| | || | || V \ || | || | |
| | | || _ _ _ _ _ \ _ _ _ || | | |
| | Intake | ||/ \ \|| | Exhaust | |
| | Valve | | \ | | Valve | |
| | Closed | | \ | | Closed | |
| | | | Rod \ | | | |
| | | | \ | | | |
\
O Crank pin journal
/
/ |
/ |
O V
Main bearings
Exhaust stroke (4)
Exhaust gasses pushed out of cylinder by rising piston driven by inertia
of flywheel (and blade).
From ignition/magneto coil >========
||
||||
Spark Plug ||||
/||\
_________________________| || |________________________
| _______________________| || |______________________ |
| | ==" | |
| | -> -> -> -> -> -> -> -> -> ______ | |
| |__ ______ ___ -> -> -> -> -> ___ \____/ __| |
|____\\____// | _____________________ | \ || /____|
|| | || || | || Exhaust
|| | ||=====================|| | || ---> gases to
______ || / ||=====================|| \ || ______ muffler
| ____||||___ ||=====================|| ___||||____ |
| | || | || ^ || | || | |
| | || | || Piston O | || | || | |
| | || | || / | || | | |
| | | || _ _ _ / _ _ _ _ _ || | | |
| | Intake | ||/ / \|| | Exhaust | |
| | Valve | | / | | Valve | |
| | Closed | | / | | Open | |
| | | | / Rod | | | |
| | | | / | | | |
/
Crank pin journal O --->
\
\
\
O Main bearings
Service Information
References
The best reference is the manual that likely came with your engine. This
will have the specific information needed to service it as well as the
recommended preventive maintenance tips. Many engine manufacturers now
have the user and service manuals for specific engine/equipment models
on-line as well as extensive general maintenance and troubleshooting
information, and parts identification and ordering.
Richard J, Rivele, Ed.
Chilten Book Company, 1993
Radnor, PA 19089
ISBN 0-8019-8323-1
Chilten Book Company, 1979
Radnor, PA 19089
ISBN 0-8019-6810-0 (Paperback: ISBN 0-8019-6811-9)
Paul Dempsey
TAB Books
Blue Ridge Summit, PA 17214
Paul Weissler
Sterling Publishing Company
Two Park Avenue, New York, NY 10016
Ross R. Olney,
Doubleday and Company, Inc., 1972
Garden City, NY
Intertec Publishing Corporation
P.O. Box 12901, Overland Park, Kansas 66212
Carmine C. Castellani & Clifford P.Seitz
ARCO Publishing, Inc., 1975, 1976
219 Park Ave. South, New York, NY 10003
ISBN 0-668-02705-3
Tom Cuthbertson and Rich Morrall
10 Speed Press
Box 4310, Berkeley, CA 94704
Franklynn Peterson
Emerson Books, Inc., 1978
Buchanan, NY 10511
Mort Schultz
John Wiley & Sons, Inc., 1994
605 Third Avenue, New York, NY 10158-0012
ISBN 0-471-53500-1 (cloth:acid-free paper), ISBN 0-471-53501-X (paper)
George R. Drake
Reston Publishing Company, A Prenice-Hall Company, 1976
Reston, VA 22090
ISBN 0-87909-724-8
A Popular Science Book
Paul Weissler
Times Mirror Magazines, Inc., Book Division, 1975
ISBN 0-06-014564-1
Time-Life Books, Inc., 1989
Alexandria, VA
ISBN 0-8094-6268-0, ISBN 0-8094-6269-9 (lib. bdg.)
The Editors of Time-Life Books
Time-Life Books, Inc., 1982
Alexandria, VA
ISBN 0-8094-3910-1 (retail ed.), ISBN 0-8094-3911-X (lib. bdg.),
ISBN 0-8094-3912-8 (lib. bdg.)
A Repair and Maintenance Manual
Walter E. Billiet
Perntice-Hall, Inc., 1982
Englewood Cliffs, NJ 07632
ISBN 0-13-814327-7 (hardback), ISBN 0-13-814319-6 (pbk.)
Walter Hall
Rodale Press, 1983
Emmaus, PA
ISBN 0-87857-446-8 (hardcover), ISBN 0-87857-447-6 (paperback)
Paul Dempsey
Tab/McGraw Hill, 1994, $14.95
Links to engine and equipment manufacturers
Try Doc
System Small Engine and Power Equipment Resource list. (This is a
copy found via a Web search. The original Weh site seems to have disappeared.)
A local copy is archived at
Sam's
Copy of Doc System Small Engine and Power Equipment Resource.
On-line small engine discussion group
This is a free (well sort of, it is advertising supported which presumably
means you probably have to tolerate banners and such but hopefully no SPAM).
"Small Engines is an open forum intended as a resource for individuals
studying small engines, business owners, home owners or anyone for that
matter. The basic purpose of the list is to serve as a forum for discussions
and distribution of information. Subscribers are encouraged to post
questions, comments, or announcements of interest to the list about small
engines and which pertain to work or theory or ideas about the current
development or past of small engines. Discussions include: electrical systems
on equipment, what works and how to do things, the effects of small engines
on the environment and a lot more."
Mower and engine parts sources
Most of the common maintenance and repair parts that are likely to be needed
are readily available and relatively inexpensive. Your place of purchase
may be most convenient but not necessarily the cheapest.
New parts and supplies - walk-in
New parts and supplies - mail order/Web
An increasing number of small engine manufacturers are providing on-line
sales of repair manuals, general maintenance items, and "how to" books
and videos. One example is Briggs
and Stratton. However, they may not have more specialized items like
head gaskets and connecting rods.
- Phone: 1-864-242-6480
- Fax: 1-864-235-6465
- Email: sales@becoparts.com
- Web: http://www.becoparts.com/
- Payment terms: Visa, Mastercard, and Discover
- Phone: 1-800-826-8563
- Fax: 1-800-294-4144
- Web: http://www.mfgsupply.com/
- Email: webmaster@mfgsupply.com
- Safety information.
- Monthly tips, FAQ-like help, and an 'ask the mechanic' service.
- Original engine service manuals and special tools.
- Equipment and engine parts including complete engines and shortblocks.
- After-market replacement parts for most popular brands of engines and
outdoor power equipment.
- Phone: 1-800-873-6721
- Fax: 1-800-873-6720
- Web: http://www.oscar-wilson.com/
- Email: oscar@i1.net
- Payment terms: cash, check, Mastercard, Visa, Discover, open account.
- Email: smallengineparts@yahoo.com
- Web: http://www.partsangel.com/
- Accepts all major credit cards, debit cards, checks, and money orders.
Will also trade chickens, pigs, and tomatoes for parts! :) Valid in
Arkansas only. :) :)
- Phone: 1-815-708-0422
- Web: www.power2go2.com/
- Email: gary@power2go2.com
- Payment terms: Cash, check, money order, Paypal, and invoice
(with approved credit)
Used parts
It doesn't make a lot of sense to search the countryside for a clogged air
filter or slightly worn engine oil :-) but it may be possible to save a
substantial amount of money if you can locate a previously owned replacement
for that bent crankshaft!
"About 10 minutes, replace the points, spark plug and a spritz of starting
fluid and 90% are fine after that!"
Comments on buying used mowers
Caution: Mowers older than about 20 years or so will not have the safety
features of modern ones (dead-man bar for engine kill and/or blade-brake
clutch). Therefore, it may make sense to avoid really old mowers without
these safety features even if they are in perfect condition.
Small Engine Specifications
Typical mechanical specifications
The following are some of the key dimensions and other specifications for
several common Tecumseh engines. Where two numbers are listed, they are
the upper and lower service (wear) limits as appropriate. One of these will
be close to the expected dimension on a new engine; the other represents the
point at which you are supposed to replace the part due to wear. All values
are in inches unless otherwise noted.
Specification LAV/H30 LAV/H40 LAV/H50 V/H70 VM/HM100
-------------------------------------------------------------------------------
Horsepower: 3 4 5 7 10
Displacement (cubic inches): 7.75 10.5 11.5 15.0 20.2
Bore: 2.3125 2.625 2.75 2.75 3.187
Stroke: 1-27/32 1-15/16 1-15/16 2-17/32 2-17/32
Timing Dimension: .060 .035 .035 .050 .070
(before TDC)
Point setting: .020 .020 .020 .020 .020
Spark plug gap: .030 .030 .030 .030 .030
Valve Clearance: .010 .010 .010 .010 .010
Valve seat angle (degrees): 46 46 46 46 46
Valve spring free length: 1.135 1.135 1.135 1.462 1.462
Valve seat width: .035 .035 .035 .042 .042
.045 .045 .045 .052 .052
Crankshaft end play: .005 .005 .005 .005 .005
.027 .027 .027 .027 .027
Crank pin journal diameter: .8610 .9995 .9995 1.1865 1.1865
.8615 1.0000 1.0000 1.1870 1.1870
Connecting rod bearing diam: .8620 1.0005 1.0005 1.1880 1.1880
(crank pin journal end) .8625 1.0010 1.0010 1.1885 1.1885
Crankshaft diameter: .8735 .9985 .9985 .9985 1.1870
(cover/blade/PTO) .8740 .9990 .9990 .9990 1.1875
Main bearing diameter: .8755 1.0005 1.0005 1.0005 1.1890
(cover/blade/PTO) .8760 1.0010 1.0010 1.0010 1.1895
Crankshaft Diameter: .8735 .9985 .9990 .9985 .9985
(flywheel/magneto) .8740 .9990 .9995 .9990 .9990
Main bearing diameter: .8755 1.0005 1.0005 1.0005 1.0005
(flywheel/magneto) .8760 1.0010 1.0010 1.0010 1.0010
Camshaft bearing diameter: .4975 .4975 .4975 .6230 .6230
.4980 .4980 .4980 .6235 .6235
Piston diameter: 2.3090 2.6260 2.7450 2.7450 3.1817
2.3095 2.6265 2.7455 2.7455 3.1842
Piston pin diameter: .5629 .5629 .5629 .6248 .6248
.5631 .5631 .5631 .6250 .6250
Width of comp. ring grooves: .0955 .0925 .0795 .0795 .0955
.0977 .0935 .0815 .0805 .0975
Width of oil ring grooves: .125 .156 .1565 .188 .188
.127 .158 .1585 .190 .190
Ring end gap: .007 .007 .007 .007 .007
.020 .020 .020 .020 .020
Top piston land clearance: .0105 .0165 .024 .023 .029
.0145 .0215 .027 .028 .034
Piston skirt clearance: .0025 .0045 .0045 .0045 .028
.0040 .0060 .0060 .0060 .053
Typical torque specifications
For proper operation and long life, you cannot just tighten critical nuts
and bolts by feel. You really don't want the connecting rod cap to come
loose while the engine is running! A Web site that has torque specifications
for many popular engine models as well as other useful information
is Outdoor Power Equipment.
Location Torque ---> Inch-pounds Foot pounds
----------------------------------------------------------------------------
Cylinder head bolts: 160 - 200 13 - 16
Connecting rod bolts (Durlock rod bolts):
2.5 - 4 HP small frame: 96 - 110 7.9 - 9.1
5 - 6 HP medium frame: 130 - 150 10.8 - 12.5
7 - 10 HP medium frame: 150 - 170 12.5 - 14.1
Cylinder cover or flange to cylinder: 65 - 110 5.5 - 9.0
Flywheel nut: 360 - 396 30 - 33
Spark plug: 180 - 360 15 - 30
Magneto stator to cylinder: 40 - 90 3.3 - 7.5
Starter to blower housing or cylinder: 40 - 60 3.3 - 5.0
Housing baffle to cylinder: 48 - 72 4 - 6
Breather cover to cylinder: 20 - 26 1.7 - 2.1
Intake pipe to cylinder: 72 - 96 6 - 8
Carburetor to intake pipe: 48 - 72 4 - 6
Air cleaner to carburetor (plastic): 8 - 12 1
Tank plate to bracket (plastic): 100 - 144 9 - 12
Tank to housing: 45 - 65 3.7 - 5
Muffler bolts to cylinder:
1 - 5 HP small frame: 30 - 45 2.5 - 3.5
4 - 5 HP medium frame: 90 - 150 8 - 12
Electric starter to cylinder: 50 - 60 4 - 5