77snojet 440 sst - Snowmobile Forum: Your #1 Snowmobile Forum

gbryanton · 03-26-2008, 10:25 PM

hello just wondering if anybody would know what would cause the piston to fail on the clutch side of engine as the proper plugs installed and gapped and gas/oil ratio of 25:1 on yamaha engine.Iinstalled a new piston previous on clutch side and it lasted approximately 1 month.Would appreciate any feedback on this topic

**smallengineguy** · 03-27-2008, 07:20 AM

Crank seal leaking or dirty carb caused it to lean out.

**RJ Gleason** · 03-27-2008, 09:11 AM

The color of the spark plug from that cyl will help to tell you what went wrong.
Most likely scenario is that the PTO seal is bad.

gbryanton · 03-27-2008, 02:35 PM

the plug on the pto side had a grayish appreance and the piston started to burn off on the exhaust side no hole through piston.Took out motor and there was oil leaking past the magneto side and a little on the pto side guess it"s time for a complete engine overhaul from the crank an up

gbryanton · 03-27-2008, 02:39 PM

thanks alot for the advice on this topic just need to find the time and parts to carry out repairs.Very hepful forum glad to have joined up.

**RJ Gleason** · 03-27-2008, 03:04 PM

Considering the age of the engine, it could have been worse.
Always a good idea to test for air leaks with an older engine that you did not do all the work on yourself.