I have a Poulan Pro mower with Briggs 25 hp V Twin Intek motor. This mower was left at a property I purchased so I do not know the history of how it stopped working. When I turn the key to start it the flywheel turns easily but seemed to have no compression, I looked in the cylinder through the spark plug hole and the Pistion is not moving, when the flywheel it truning. I have checked the flywheel and the nut and the tapered end of the crank shaft are turing together (although I have not pulled the flywheel off yet). I am getting spark to the plug, however it is usless with out a moving pistion. Is there some sort of shear pin on the crank? Or is the crank broken internally. There is NO noise from a broken connecting rod or anything else in there that I can think of. I hope not to have to tear this thing all the way down. This motor only has 200 hours on it.

Any help will do.

Thanks

Dirtbike

The shear pin is between the crankshaft and the flywheel.

At low RPM there may not be any compression. You have to turn the engine backwards manually to feel compression.

Busting a rod is entirely possible, but hat kind of stuff usually happens when you run an engine without oil. Yep, when I was 10 or so, Dad said, you broke it. You fix it. So I rebuilt an engine that thew a rod with help from Dad. To this day, I always check the oil.

Sounds like you have a broken rod, you may not hear any sound because someone may have turned the engine to where the piston has stopped now. Push the piston down into the cylinder and then turn the engine by hand to see if it moves.