Was given a Yardman 18.5 HP Briggs I/C OHV II riding mower that doesn't run. I can spin the top of the engine with very little resistance, it just turns. He said one day he started it, the throttle went sky high and he heard a "snap" sound before it shut itself off. I am assuming that this engine has a shear pin, and that it has been sheared off. But I am not the small engine pro, just the first thing that comes to mind. Anyone else have any comments?

Would really like to know if anyone thinks it is worth the effort to take the head off and repair it. Mower only seems to be a few years old and looks to be in good shape, was kept under cover for a couple years.

Thanks.

More then likely the "snap" was a connecting rod that broke, but it could be something else, although it probably is not the key. Need to try and ascertain if the piston is moving in the cylinder when you spin the engine over.

Heh, sky high eh? More than likely a broken connecting rod as said above. You may also want to check the governor linkages...

and what would the govenor linkages have to do with the "snap"?