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Very interesting link. On page 37 there are pics of nearly identical damage. But the angle of my flake (opening upward) seems to indicate that I damaged it on installation. Not knocking force from above.
Here's a link to an interesting Kolbenschmidt Piston Failure doc - sure looks like ring land fracture from Knocking (or hydraulic lock?)
https://cdn2.ms-motorservice.com/fileadmin/media/MAM/PDF_Assets/Piston-damage-recognising-and-rectifying_51730.pdf
I loved that document when I first found it. Should be sub titled - '50 Ways to Break Your Pistons'
There are some MESSED UP pistons in there.
It is indeed suspicious that I would have done the same thing twice on the same cylinder.
I know I'll be SOOOOOPER careful putting the pistons back in this time. I always am, but a 'normal' amount of careful. Just gently tapping them in with the plastic end of my light weight plastic tappy hammer. With a light coat of engine oil on everything.
And double check those ring gaps, although based on bobxyz's link it's probably not butting rings. Just some very slight damage on install, followed by me revving the piss out of it for many thousands of miles. vroom vroom.
... 93 octane pump gas...They're all 4 certainly jetted and set up identically.
It's a pretty high compression ratio.