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.
|NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Engine overhaul procedure
1994-2007, Samuel M. Goldwasser. All Rights Reserved. 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. 2. There is no charge except to cover the costs of copying.
I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.
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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
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!
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.
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.
Now it is time to get down to business! As noted, depending on your situation,
not every step will be needed.
- Disconnect and secure the spark plug wire.
- Drain the gasoline or remove the fuel tank and store in a safe place.
- Drain the oil from the crankcase/oil sump. While this is not essential
for all overhaul operations, it will eliminate any risk of oil pouring
out or going where it should not when you turn the engine over or on its
side. In addition, this further reduces the risk of explosive fumes which
might result if excessive gasoline has contaminated the oil. Finally,
now is a good time for an oil change! Refer to the section:
An oil change isn't really a big deal. (However, you
won't be refilling until later.) Don't reuse the old oil even if you recently
changed it and dispose of it in an environmentally friendly manner.
- Brush or vacuum off the exterior of the engine above and below the deck
and then wipe it down with an old rag to remove decayed leaves, grass
clipping, dirt, oily grime, dead (or live) rodents, whatever. The cleaner
it is when you actually start work, the better off you will be and there
will be less chance of contaminating the interior.
- Detach (and label if there is any doubt about how they are connected)
any throttle or dead-man control cables.
- Remove the blade (or anything else driven by the crankshaft). See the
section: Non-violent blade removal. Don't lose the
locking key if it is separate!
- Remove any auxiliary drive (self propelled) or power take off. This
may be a belt or chain above or below deck.
- Disconnect any electric start wiring from the mower.
- Check for and remove anything else that would prevent the engine from
being detached from the equipment.
- Remove any trim pieces which cover the engine. Depending on how much you
paid, the engine may be nearly bare or have multiple plastic doodads
covering up what is essentially that same bare engine!
- Remove the gas tank if you have not done so already. A spring loaded
screw clamp may be used to attach the fuel line to the tank - use a pair
of pliers, socket, or screwdriver as appropriate to loosen it.
- Remove the oil filler pipe, if any. This is usually fastened to the
shroud/blower housing with one or two small screws. Thread these back
into their holes finger tight so they will not get lost.
- Remove the shroud/blower housing. This is usually fastened with 4 small
bolts (they may be different sizes - replace in the threaded holes so they
will not be lost. If there is a primer tube running to the carburetor,
disconnect it at whichever end is convenient.
- Remove any electric starter components - starter motor, gears, etc.
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.
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.
Some mufflers simply screw into the cylinder using pipe threads. Others
are mounted with a couple of bolts.
- Remove the muffler. Use penetrating oil (e.g., Liquid Wrench or WD40) if
the mount is heavily rusted or corroded and does not yield to normal efforts.
- It is ok to ruin the muffler in the process. Mufflers are inexpensive and
you probably needed a new one anyhow. Just do not damage the cylinder
threads as the metal is relatively soft.
- If the muffler comes off intact, inspect for serious corrosion, holes,
or other damage and figure on replacing it if needed.
This can be left in place but will be susceptible to damage.
- If you will need to remove the crankshaft or get under the flywheel to
check or adjust the points (non-electronic ignition), then now is as good
a time as any to remove it. See the section: Flywheel
- Inspect the flywheel and set it (and associated washers, starter clutch,
etc.) aside in a safe place - away from steel filings that will be attracted
to the powerful magnet!
- Thread the flywheel nut back onto the shaft and then protect it with a rag
or paper towel secured with an elastic band.
- Inspect the high tension lead for cracking or broken insulation. Temporary
repairs using several layers of electrical tape may be made but replacement
is best for long term reliability.
- Inspect the stop wire and any others for similar damage and repair or
replace parts as needed.
- The electronic (e.g., Goldkey or Magnetron) ignition can be removed as a
unit since there is nothing under the flywheel except possibly a (plastic)
sleeve/spacer. Inspect the potted unit for cracks or other damage.
- For point type ignitions, the magneto coil along with the components under
the flywheel (points, condenser, cam) can be easily removed if the flywheel
has been pulled. Inspect for worn, pitted, welded, or corroded points
and other damage.
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.
- Use the proper size spark plug or deep socket to remove the spark plug
counterclockwise. Inspect the spark plug and threads in the head for damage.
- Use the proper size socket to remove the (usually 6 to 10) head bolts
counterclockwise. It is best to loosen each a half turn at a time
in an alternating pattern until they turn freely to minimize possible
stress on the head. They will be fairly tight but should not be frozen.
Check each one after removal as some may be longer than others and then
must go back in their respective holes. Hold the head with one hand
as you remove the last couple bolts - it should pop right off.
- Separate the head and head gasket from the cylinder. This should occur
easily without requiring your persuader.
- Inspect the head, head gasket, and cylinder mating surface for major
damage. While it may look really ugly, once the carbon is removed, the
metal should be virtually like new.
- Remove built up carbon from the head, valves, piston, and cylinder. This
is best accomplished by chipping it away with a soft metal tool like a
scrap of aluminum. Take care if you use a steel paint scraper or screwdriver
not to scratch the relatively soft cylinder or piston. WD40 will often
help to loosen this carbon buildup. Most of the carbon will probably be
on the exhaust valve and on the exhaust valve side of the head and piston.
Remove the valve cover on the side of the engine next to the valves.
Use a feeler gauge to check the gap between the valve lifter and valve
stem with the valve lifter in the relaxed - lowest - position. A typical
value is .010 inches. Excessive clearance will require replacement of the
valve or valve lifter. There could also be too little clearance - which is
also bad - but the valves stems can be ground down to repair this problem
which is either a defect in manufacturing or a result of a cam shaft
replacement which is oversize.
Use a valve spring compressor to remove pressure on each valve.
The retaining clip or split cup should now be free. Remove these.
The valve should now slide out.
Loosen the valve spring compressor and remove the spring and any other
hardware. Don't interchange the intake and exhaust valve springs.
Remove the built up carbon deposits from the valves and valve seats
using a soft metal scraper. Some WD40 may help to loosen the caked on
Inspect the valves for serious burning or pitting especially on the
seating (angled) surfaces. Once free of any carbon, they should be
smooth and undamaged.
Similarly, inspect the valve seats for serious burning and pitting.
Inspect the springs for rust or other damage. Stand them on a flat
surface and check for serious droop/tilt. Measure their free length
and compare with your engine specifications.
We are now going into the lower section. I can hear you saying "Joy!".
- Check the crankshaft for burrs at the blade lock key or other key and/or
where any front wheel drive pulley setscrew was tightened. It is essential
that these be carefully removed with a fine file before you attempt to
remove the cover to avoid damage to the main bearing. In addition, any
rust and/or dirt buildup must be removed with steel wool, sandpaper, or
emery cloth to allow the shaft to pass through the main bearing without
damaging the bearing or oil seal. Remove all traces of rust and grime
but don't go overboard - it doesn't need to shine. Wipe with a very
slightly damp cloth to remove ALL abrasive residue.
- Set the engine flywheel-side down on wooden blocks so that the flywheel
mounting shaft is clear of the table.
- Once again, wipe down the underside of the engine, especially around the
crankcase/oil sump mounting bolts and the seam where the cover will
separate from the engine block.
- Remove the 6 to 10 hex head crankcase/oil sump mounting bolts and set them
- Use a soft rubber mallet if necessary to help free the cover. If mild
persuasion doesn't work, check for any bolts you may have missed.
- As the cover comes free, gently lift and turn at the same time. It should
slide right off the crankshaft. If there is any resistance, you probably
didn't find all the burrs or rust. Go back, identify, and correct the
problem. Don't force it as you will end up with scratches on the bearing
surface and/or damage to the oil seal.
- The gasket will likely tear in the process of removing the cover and
will need to be replaced. It is not worth trying to repair it. You
will have to scrape the remnants of the old gasket off of both mating
surfaces before installing the new one (later).
- Check for any washers that may come free with the cover. There will
be at least one on the crankshaft. It may be sticking to the bearing
surface on the cover.
- Usually, the flyweight governor is just left in place unless parts need
to be replaced. Inspect it for damage to the gears, flyweights, or cup.
Individual parts can be replaced if needed (and if you can get them!).
The post is a press fit and should not be disturbed unless damaged.
- Remove the camshaft driven plunger type oil pump. This is in two sections
which have a definite relationship (the flat faces out). Inspect for damage
and set aside.
- Carefully rotate the crankshaft until the timing marks align. These will
be a line, dot, or hole on the camgear and crankshaft gear. For most engines,
these should line up perfectly with each other at one position of the
crankshaft. However, on some Craftsman engines, they are offset by one
tooth. Check and note this before removing the camshaft/camgear!
- With the timing marks aligned, valve pressure should be released (if
you removed the valves, this won't matter) on the camshaft and it should
slip out easily.
- Inspect the camgear for chipped or broken teeth and wear. There should
be no chipped teeth and no detectable wear on any of the gear teeth.
Chipped teeth or significant wear will require replacement.
- Inspect the cam lobes for wear or wear. There should be no detectable
wear and no damage.
- Check the compression release mechanism on the camgear for damage and
free operation. The weight should snap back to the shaft when released.
The little lift pin should move smoothly.
- Remove each of the valve lifters and inspect for wear. There should be
no significant wear. Note which went where so that they can be replaced
in the same location. Most are of the same length but once a wear pattern
is established, replacement in the same location is desirable. Sometimes,
they are of different lengths and then this is more critical.
- Rotate the crankshaft so that the rod bolts or nuts are accessible.
- Bend out any lock plate that may be associated with the rod bolts or nuts.
Many Tecumseh engines use 'Durlock' rod bolts with integral locking
serrations and there is no lock plate and no lock washers. Note: Durlock
bolts, lock plates, or lock washers should always be replaced with new ones
if removed and not be reused. You really don't want the rod coming apart!
- Use the proper size socket to loosen the rod bolts or nuts
counterclockwise. Start with small equal increments on each of them until
loose to equalize stress.
- Remove the bolts or nuts and cap. Note the orientation of the cap and
rod. If yours is the slant type, this is easy. Otherwise, look for match
marks, casting numbers, or other identifying marks and make a diagram in
- Where bolts protrude from the rod, immediately cover these with some bits
of rubber tubing or tape to prevent them from hitting and dinging the
crank pin journal or other precision surfaces.
- Remove any carbon ridge you find at the top of the cylinder. This will
catch the rings and prevent you from removing the piston or if force is
used, break the rings. Usually, it is a simple matter of scraping with
a piece of soft metal like aluminum. On rare occasions with a really
well worn engine, enough of a metal ridge will also be present to require
the use of a ridge reamer tool.
- Push the piston up and out of the cylinder bore. The rings will expand
but will not pop off unless they are actually broken.
- Replace the rod cap and finger tighten the nuts or bolts. This will help
to protect the bearing surfaces from accidental damage.
- Inspect the piston for damage. There may still be significant carbon
deposits but once these are carefully scraped off, the piston should be
fairly smooth. There may be some vertical scoring but a modest amount
of this is not serious.
- Inspect the rings and ring grooves for damage. It is usually not necessary
to actually remove the rings from the piston to do this - which should be
avoided if possible to minimize the chance of breakage. The outer surface
of the rings should have an almost polished appearance with no significant
pits, scratches, or corrosion. There should be no chips or other visible
- If you must remove the rings, use a ring expander if possible and make
sure you note the exact orientation - top/bottom and location - for each.
- If you are removing the piston pin, note the orientation of both the
rod and pin as they must be returned in the same relationship. Pistons
are not symmetric! Look closely and you will see that the pin is offset
a fraction of an inch to one side. This is done to optimize the center
of force on the rod bearing and rotating crank pin journal.
- Use a pair of needlenose pliers to remove the 'circlip' from one side.
The piston (wrist) pin usually floats (moves easily) in between the two
circlips but a slight lip of metal (probably resulting from the pin
banging back and forth) may prevent it from being easily removed. Very
slightly scraping around this lip will free it up or you can remove the
other circlip and then use a drill or arbor press to push the pin out far
enough to free the rod. There is no need to remove the pin entirely.
Then, there will be no question as to the direction upon reassembly.
- Lift while rotating the crankshaft out of the top bearing. There should be
no resistance (unless you forgot to remove something).
- Inspect the crankshaft to determine if it is bent. Any deviation from
perfection is cause for replacement. The proper way to do this is with
some V-blocks and a run-out gauge. However, you won't have these tools
so a visual inspection is the best you can do. However, unless your
blade kissed a boulder, a bent crankshaft is not likely.
- Inspect the small gear for broken teeth and wear. There should be no
chipped teeth or detectable wear of the gear teeth. If there are chipped
teeth or significant wear, then this gear and the camgear will need
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.
- Check for any washers at the flywheel end of the crankshaft and set these
aside. There are probably none.
- The breather allows the pressure inside the crankcase to vent to the
outside and should result in negative pressure inside as this contains
a (leaky) one-way valve.
- The breather cover is under where the flywheel is located.
- Remove the screw to remove the cover plate. There is a gasket but
it will probably separate cleanly.
- Check the spring and valve disk for rust, dirt, and wear. They will
likely be fine. Make sure the small vent hole is clear.
- Replace the cover as there is nothing else to do in there.
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
- Do not remove the oil seals unless you intend to replace them. If oil
leakage has not been a problem and you don't think any damage resulted
from removing the crankshaft, leave them alone. It should be possible
to replace the oil seals after reassembly if oil leakage turns out to
be a problem.
- It is very unlikely that the flywheel side oil seal would be defective
- The PTO/blade oil seal can be damaged by neglecting to completely remove
burrs from the crankshaft before removal of the crankcase/oil sum cover.
- To remove the oil seals, use a screwdriver to pry them out from the
crankcase/oil sump cover and/or the flywheel side of the crankcase.
Take care not to gouge the mounting surfaces.
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:
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.
- Crank pin journal and rod bearing. Inspect for wear, pitting, and scoring
on both the crank pin journal and the inside bearing surface of the rod and
cap. On a new engine, both of these surfaces are nearly mirror smooth. On
a well worn engine, there may be significant scoring due to particles from
the oil getting trapped. An engine that has failed due to a severe lack of
lubrication may result in some pretty spectacular failures of these parts.
Minimizing wear and the change of catastrophic failure is the primary reason
for performing regular oil changes.
- A few score marks around the entire circumference of the journal are
unimportant as long as they represent a small percentage of the surface
- Scratches, pitting, or score marks that run side ways are more serious.
If slight, polishing with very fine emery or crocus cloth may be all
that is needed. If they catch a fingernail, this may not be enough.
- A serious out-of-round condition is unacceptable.
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!
- Main bearing - PTO (blade) end. Inspect for severe scoring, corrosion,
or other damage. It may no longer be mirror smooth but should not appear
- Main bearing - flywheel/magneto) end. Inspect for severe scoring,
corrosion, or other damage. This will probably appear almost like new even
on an old engine as there is a lot less load on this end and it is relatively
well protected and well lubricated.
- Cylinder. Inspect inside the cylinder for excessive wear and scoring.
If it appears fairly smooth without much scoring, it is probably ok
but only exact inside measurements would confirm.
- Piston. Examine the sides for vertical scoring. There will probably be
some but as long as the piston is not mostly score marks, it is probably
fine. Only exact measurements would confirm. Check for damage to the
lands - the surfaces between the ring grooves. If any are cracked or
broken, the piston will need to be replaced.
- Piston (wrist) pin. This should be mirror smooth. There should be no
detectable free play if you try to jiggle the rod.
- Rings. Inspect for damage, pitting, and scratches. The outside surfaces
should be pretty much mirror smooth. Use an appropriate sized feeler
gauge to check clearance between the rings and piston grooves.
- Oil passages. Inspect and use compressed air if necessary to clear the
various oil passages in the crankcase/cylinder, camshaft, connecting rod,
and crankshaft. The typical small Tecumseh engine has a hollow camshaft
which is part of the oil pump and drilled passages in the crankcase. The
oil path is from the plunger/barrel oil pump up through the center of the
camshaft, over top via the passages in the crankcase to lubricate the main
bearing (flywheel/magneto end) and also to drip on the connecting rod and
crank pin journal. Some larger engines also have drilled passages in the
crankshaft and connecting rod. There is even an oil pressure test port
normally sealed by a small screw. A typical pressure measurement on an
engine running at full speed is 7 psi but you won't measure this so just
make sure everything is clean and clear.
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.
- Oil seals: If you removed the oil seal(s), clean the inside surfaces
where the seals go and install new ones by pressing them in straight and
square with a block of wood and rubber mallet or better yet, use a drill
press or arbor press. Make sure you get the correct side facing out!
Installing the new oil seals after the crankshaft has been replaced may
be easier. There is a special tool for this but a piece of pipe that just
fits over the crankshaft cut off square will work just as well. Remove any
burrs on the crankshaft to prevent damage to the new seal and take care that
any rubber lip on the seal does not get folded over.
- Breather: If this was removed, replace valve plate, spring, gasket, and
cover. However, this is probably already assembled.
- Valves: Use a valve spring compressor to fully compress the spring for the
intake valve and install the valve, any washers, and retaining clips. Do
the same for the exhaust valve. Install the valve cover.
- Piston rings: Replace any that were removed. Use a piston ring expander
if available or your hands to expand the rings and slip them over the piston
and into their proper grooves. Note orientation and position! Avoid
scratching the relatively soft piston. Do not expand more than needed -
the rings are fragile.
Note the typical arrangement (from top to bottom):
- Compression ring (solid).
- Compression ring (solid).
- Oil ring (slotted with internal expander spring).
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.
- Piston pin and connecting rod: Put a few drops of engine oil on the
pin, position the rod, and then slide the pin into place. Use a press
if it is a tight fit. Use new circlips to secure the pin. Make sure
you get the orientation of both the rod correct! It is also desirable
to install the pin in the same orientation as it was originally. If the
pin was never entirely removed, this should not be a problem.
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.
For the following steps, position the engine on wooden blocks blade/PTO side
- Crankshaft: Using a gentle rotating-while-inserting, place the crankshaft
into the flywheel/magneto-end bearing. Use engine oil to prevent scratches.
Take care not to bend over the lip of the oil seal.
- Piston into cylinder: Coat the piston and cylinder wall with engine oil.
Orient the rings around the piston so that the gaps are staggered by 90
degrees and not above the pin location. Suggest from top to bottom: 45,
135, 225 degrees. Use a piston ring compressor (commercial or home-made).
Tighten until the rings are fully compressed and then release just a hair.
Position the piston in the correct orientation - rod with respect to
crankshaft - and gently tap into cylinder using a wood block and rubber
mallet. If it hangs up, the compressor is too loose. If it does not
move at all, the compressor is too tight.
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.
- Rod and cap to crankshaft: Coat the crank pin journal with engine oil.
Position the crank pin journal and rod bearing so that they are in contact.
Place the rod cap in position - noting match marks. Using a new lock plate,
lock washers, or rob bolts, as appropriate, hand thread the nuts or bolts on
as far as they will go. Jiggle the cap to adjust and then tighten some
more by hand.
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:
- I use a basic 3/8" deflecting beam type torque wrench - nothing fancy.
To this, I add a 3/8" to 1/4 inch adapter (short) and a 1/4" socket.
- Position the piston/crankshaft to provide the most clearance for each
nut or bolt. These will differ.
- This can also be done with an open end wrench and spring scale but the
torque wrench is so much easier!
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
- Valve lifters: Install the valve lifters in their respective holes.
- Camshaft/camgear: Carefully rotate the crankshaft until the timing mark
faces the camshaft bearing location. Slip the camgear in place so that the
timing marks exactly align (or if your engine is one of those exceptions,
so they are off by one tooth - see your engine manual if in doubt). For
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).
- The corresponding timing mark on the crankshaft is either a beveled tooth
on its gear or in line with the keyway.
- If the engine has a Craftsman type (float) carburetor, advance camshaft 1
tooth clockwise (except for the Craftsman variable governed fuel system,
whatever that is!).
- Oil pump: Install the two piece oil pump. The flat must face out.
- Crankcase/oil sump cover (temporary): Install the washer(s) that go on
the crankshaft. Without using a gasket, install the crankcase/oil sump
cover. Use a gentle twisting motion and take care to avoid damaging the
oil seal. Slip the ball end of the oil pump plunger into its cavity in
the cover before it is fully lowered. With a little jiggling, the cover
should seat properly. Thread a couple of the mounting bolts in hand tight
to hold it in place.
- Test for free rotation: Use the blade adapter and key as a means of
grasping the crankshaft and rotate it through two complete revolutions.
There should be no binding of parts though you will feel the resistance of
the piston as it moves up and down in the cylinder and the valves as they
are lifted once in every two revolutions (which you will also see from above).
- Remove the cover. Double check that the mating surfaces are free of old
gasket material and dirt. Use a new gasket. Again, take care not to
damage the oil seal and line up the ball on the end of the oil pump plunger
so that it fits in its cavity in the cover as it is slid into place.
Install all the bolts and tighten in a staggered order incrementally to
the proper torque.
- Cylinder head: Position the cylinder head and new head gasket and install
all the head bolts finger tight. If any are of a different size, make
sure they go in the proper locations so that they do not bottom out or
engage too few threads. (Tecumseh bolts seem to be all the same size.)
Tighten the head bolts in the recommended sequence in 3 or 4 equal
increments to the torque specified for your engine.
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.
/| | | | | | | | 8 |
|5| | | |3| | | |=|=O |
| O=|=|=|=O=|=| | | | |
/| | | | | | | | _ | |
|1| | | | | | | | |O| |2|__
| O | | | | Spark Plug O |
| | | | | | | | | | | | | |
\|7| | | |4| | | | | | | |
| O=|=|=|=O=|=| | |6| | |
/\| | | | | | | |=|=O |__|
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:
- Ignition: Install the components (if any) that go under the flywheel
(e.g., points, condenser, cam). Install the magneto coil or electronic
ignition module. Temporarily position it so that it is as far away as
possible from where the flywheel will go. Tighten the bolts.
- Set the point gap and ignition timing (point type ignitions systems only).
See the section: Setting the point gap and ignition
- Flywheel: Place any inside spacers proper side up onto the crankshaft.
Position the flywheel key in the keyway and then install the flywheel
onto the shaft. Jiggle it a little to seat solidly. It should not now
move from side-to-side at all. Add the washers, starter cup, and flywheel
nut. Screw the nut on by hand and then tighten securely (but not to full
torque necessarily at this time) using a socket wrench. Torque to
specifications once the engine is mounted as this will be a lot easier.
- Set the flywheel magnet-magneto gap (if you have not done this already):
Place an appropriate spacer (e.g., .015 inches) between the flywheel magnet
and magneto pole pieces. Loosen the magneto coil mounting bolts. The
magnet will draw the pole pieces tight against the spacer. Tighten the
bolts to the recommended torque.
- Install the spark plug with a new washer (and a dab of anti-seize
compound). First, thread the plug in by hand to get it started and then
tighten to specifications (15 to 30 ft-lbs typical).
- Install any electric starting components.
- Install the muffler. A dab of anti-seize compound will make removal of
exhaust system components much easier at a later time should the need arise.
- Carburetor: Position the carburetor assembly in its proper location.
- Reinstall the throttle and governor linkages: Where there is no speed
adjustment or idle position, the direct governor linkage goes in the hole
closest to the engine and the spring hooks onto a fixed vertical metal
strip with only one hole at one end and the lower hole in the governor
lever at the other. Thus, in operation, the spring attempts to keep the
throttle open and the governor pulls on the throttle to close it. Increased
spring tension results in higher speed. Don't get these backwards when you
go to reinstall the carburetor on the engine!!!
- Reattach the primer tube, if you removed it at the carburetor end.
- Reattach the stop switch wire, if any.
- Install the carburetor onto the engine with a new gasket if needed.
Tighten securely to the proper torque (6 to 8 ft-lbs).
- Double-check that the throttle linkage and governor spring are in the
proper holes and nothing is binding - you should be able to move the
throttle back and forth without any sticking or tightness. It should
return to the full counterclockwise position instantly as a result of
the governor spring tension.
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:
- Remove the three mounting bolts from the bottom of the engine. Position
the engine on the mower deck and install these bolts finger tight. Then,
use a socket wrench to tighten securely.
- Tighten the flywheel nut. Brace the flywheel against something solid
and tighten the flywheel nut to the recommended torque (30-33 ft-lbs).
- Shroud/blower housing: Position and install using the proper bolts.
- Oil fill pipe: Put a little engine oil on the O-ring. Position the
fill pipe into the oil hole in the base of the crankcase/oil sump cover.
Make sure the O-ring seats inside the oil hole. Tighten the screw(s).
- Gas tank: Slip the gas tank into its mounts and tighten any screws.
Connect the carburetor fuel hose to the gas tank.
- Trim pieces: Reinstall any trim pieces.
- Reattach any dead-man and throttle cables to the engine.
- Install any front wheel drive components - pulley to crankshaft (using
proper key) and belt, or chain drive.
- Install the blade adapter and blade. Tighten to the recommended torque.
- ADD OIL!!! Add fresh engine oil to just below the top of the oil filler
hole or just below FULL on the dipstick. This will be about 1-1/4 pints.
- Use the starter cord or electric starter to crank the engine a few times.
This will help to distribute the oil.
- Add a small amount of gasoline to the fuel tank - say, a half a glass.
- Engine overspeeds due to screwed up governor or linkage.
- Unusual knocking or banging due to parts hitting one another.
- Excessive black, white, or blue smoke from exhaust (or 3 foot flames,
- Leakage of oil or gas.
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
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!
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