The sections that look "raised" (circled in green) here are actually flush with the bore material, they look raised because the surrounding material is worn away



I didn't learn a whole lot from having it torn down to be honest. I suspect the initial cause was overheating, piston expanding too much and scraping into the cylinder wall.

I'm going to be removing the crankshaft and pistons and I think seeing what the piston on that cylinder looks like will provide a little more information.