Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Need to run a leak test on a briggs 15.5 on a craftsman tractor for a friend. Briggs says to hold the piston at tdc with the crank holder and a 1/2" breaker bar. In this case the engine is still on the tractor. Would engaging the pto hold the piston? If not, would the proper socket and breaker on the flywheel nut be enough to hold it? Can't see taking the engine off the tractor until I know for sure if the problem is rings, valves or just a head gasket. Thanks

okay here we go .

a compression test wont work on hardley any small engine because of whats called compression release.

this is a mechanical system used to actually bleed off a little bit of compression so the starter can roll the motor over.without it things will break easily.

so we use a cylinder leak down tester.

with the piston held at top dead center on the compression stroke we apply compressed air through an attachment at the sparkplug hole.we use a guage to determine how much of this compressed air is being lost.

and it is quite easy to determine where the air is lost to ...valves ...rings ... head gasket.

we usually hold the engine from turning over with a breaker bar on the bolt that holds the PTO pulley on.

the flywheel bolt will probably loosen and come out.

hope this clears things up.

a quick way to determine if an engine has enough compression to run is to roll the engine backwards by hand. you will FEEL it come up to compression,now just give it an extra snap against compression.if it bounces back its okay.

try this on a known good engine and see what i mean.

this works because the compression release is designed to operate when rolling the engine normally,if we roll it backwards we are not using the compression release.

you may have to remove the flywheel shroud to do this .

later chris