I'd have thought the crack would be near the gap in the ring (do they really expand that much to cover that much space?)I’m gonna have to say insufficient ring end gap.
The PN on the piston is from Wiseco. It’s a 4032 alloy forging..typically ran with very tight tolerances in the bore, because it doesn’t expand very much ( comparably) when it gets hot.
But the rings do...
The wrong end gap will cause them to butt when exposed to heat from too much of a power adder, and not enough timing removed. Certain alloys expand at different rates than the ring, and a “too tight” ring will basically cut the ring land right off the piston.
Thats what that looks like was starting to happen to me.
Does the ring end gap move around the piston or does the ring stay in the same place once in the bore? I've always wondered about that.