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To me it's classical, something loose. Seen it a few times and it's the pin clips or buttons but they make similar marks. Something had to get in there.. Maybe from the oil control ring. It looks suspicious.
This came out of a racecar engine Im rebuilding. There were a number of issues found before I saw this. Jetting was much less than I would expect for the application and the advance mechanism in the distributor had seen better days. What fuel was being run by the PO considering the high compression ratio is an unknown but bore size or piston to wall clearance wasn't the cause of this similar meltdown. The piston is getting too hot.
Total seal is a different animal compression loss is cut way back that actually cools the pin area of the piston ay hi speed
and the engine speed was way to hi for the piston to wall clearances seen this before as well — i see the oil ring separator is in the same place as the oil stainless ring this will happen when the rings are chartering — so materials - sizing and speed of the piston comes into play
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