Because of the inbuilt decompressor, i think the procedure for testing compression as outlined by Briggs is to rotate/spin the engine by hand toward the top of the compression stroke (a sort of flick of the wrist) and the engine is meant to bounce back a certain amount.

Grumpy will know more about it.

As the piston raises up to the top of the stroke it builds compression and just before TDC the exhaust valve will lift slightly, so its like theres two TDC's on the compression stroke if you are turning the motor by hand. Well two stages.
I would assume the theory is that in the first part of the compression it should build enough. The above spin method does have its flaws, any drag on the crank will effect results as will altering the reciprocating weight of the engine. The Greenfields pulley being a billet of steel weighs a hell of a lot more than the pressed steel pulleys ive seen on other machines.

You can use a tester, if you have another motor there similar or same, and compare the PSI readings. Something better than 60 or 70 psi rings a bell.

I dont bother any more, i used to compression test the mower engines (3-5hp) but i just pull the head off and have a look now. Set the valve clearances and put it back together. Then see if it smokes. Sure compression pressure is relative to ring wear but so is smoking, a motor that does not run at full efficency due to worn rings will still do its job for a long while, but one that smokes will be a hard sell.


I would suggest you do the same.
Fix the starter.
Check the spark, see if thats OK.
Pull the head off, inspect the bore and set the valve clearances.

Whats the carb like?? You said that the filter is missing, has it had water in it?? Has water got in the motor.
Carb (and exhaust?) will need to come of to check the valve clearances.

If the motor does not pass the test it is very sellable as parts and/or worth keeping.


With a cast iron flywheel the motor is safe to start and run with nothing on the crank.
I would suggest an old table or desk, drill a hole, cut a hole out with a jigsaw and bolt the motor down with 2 bolts.

Cheers, Bob.