The conditions you have described is what us old
timers call "galling the piston" it is caused by
overheating the engine in such as a long hill or
running too fast for conditions, most of the time it
will occur when the oil temp gets above 250F, I don't
know what the cylinder head temp would be but most say
over 450F on the heads the valve seats start having
problems. Just gotta watch those temps on the air
cooled engines. Phil

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