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
|NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Flywheel removal
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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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:
- A rectangular or D shaped piece of soft metal that locks the flywheel
and shaft. You should be able to see if the two identically sized slots
are still aligned.
- A piece of soft metal with an L-shaped cross section. The slot on the
crankshaft is narrower than the slot on the flywheel and is slightly offset
(thus, the L). Again, it should be obvious if the two slots are still
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
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:
- The best way by far is to use a special puller designed for your particular
engine. Briggs & Stratton and Tecumseh flywheels usually have 2 or 3 holes
placed around the center of the flywheel which are used with special puller
blocks. These have self tapping bolts which you thread into the holes and
then tighten down nuts to pop the flywheel off of the crankshaft. I have
made my own blocks for this purpose from scrap steel. If you have a drill
press, it is not difficult. Alternatively, you can purchase these from the
engine manufacturer. The use of a puller really does reduce the use of 4
letter expletives and virtually eliminates the chance of damage to the
flywheel or crankshaft by the alternative techniques.
|___| |___|<-------- 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!)
//////| |///|:----:|///| |//////
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.
- A 'knock-off tool' is a special closed-end nut that you thread onto the
crankshaft in place of the normal flywheel nut. You then are supposed to
pry under the flywheel with a pair of large screwdrivers while tapping
the knock-off tool with a soft hammer. Aside from the fact that as
described, this requires 3 hands, this may or may not work easily.
Depending on conditions, the flywheel may pop off at the first tap or
may stubbornly refuse to budge no matter how much you whack. If not done
properly, it is possible to bend the crankshaft - very expensive. Some
people also worry that the shock will damage internal parts or even
partially demagnetize the magnet on the flywheel. Thus, my preference
for the puller unless the first couple of taps releases the flywheel.
- Many engine books will simply recommend threading the flywheel nut back
on flush with the end of the shaft and tapping this with a hammer as
above (with the 3 hands). The risk here is that the threads may be
damaged in addition to the possibility of bending the shaft or causing
other damage. Use a piece of soft metal - aluminum, brass, or lead - to
protect the end of the shaft and nut. In any case, only use this approach
as a last resort.
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