So what is everyones opinion of why this happened. Fresh rebuild. Rev 800. Never taken above half throttle...okay, so maybe an occasional bump to 3/4, but never full.
Cylinder looks okay except a bit of build up from the piston.
The whole story on this is that it belongs to my son's friend, they borrow my garage to work on it.
He originally had a problem with the right cylinder. The intake side of the piston had busted and compression was down to 60 PSI (mag side), PTO side was at 115 PSI.
They replaced both pistons and slapped it back together. I thought they knew what they were doing, but evidently the first rebuild was done incorrectly. One piston was backwards and the rings were upside down. It busted a ring and tore up the cylinders.
New/used set of cylinders and new pistons, they paid closer attention to the ring placement, etc, etc. Got it back together and ran it for about 2 hours before it lost compression again. 5 PSI on the PTO, 130 PSI on the Mag.
Pulled it apart and discovered the melted piston.
I told them they need to pull the whole motor out this time and check everything for leaks, etc. I'll be helping out a lot closer on this (hopefully) final rebuild.
One note on this, the exhaust valve was pretty beat up on that PTO side after this. He'll replace it, but it looked like something was hitting it hard. Wondering if these can be put in upside down or something. I've never really worked with exhaust valves. Pulled the ones on my old Summit off and cleaned them, but they looked symmetrical.
Not upside down, but backwards with the bevel facing the wrong way.
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