Do we really know how close to round any cylinder bore remains as the block warms up? Particularly if there's a casting flaw that affects heat flow and temperature distribution (and hence expansions/distortions)?
"Oval" was the best word I could come up with to mean "not quite round". Not visibly oval or necessarily even a nice symmetrical non-round shape. You guys have a deeper level of engine building experience than me (I do have a little), but the thermal transient analysis work I did from time to time before retiring gives me a fair idea what might be happening.
Yes I understand all of that too. Flaw in the block possible that got through. But they x-ray blocks to check for core shift well at least one from each batch. Well pistons are not round the cam shape in tell they get temp in them especially forged pistons they grow hint reason why there set with more clearance when cold