[1JEWLDSSRS]

It is a real thing. My old 72 Challenger 340 ci did it back when. Not sure what causes it, but when we rebuilt the engine and took the old pistons out, you could see where the piston skirts were hitting the cylinder walls and scraping them. I think it probably was due to the rings being excessively worn out and not sealing them like they should, and therefor causing the pistons to "slap" the cylinder wall on the up and down stroke by not being tight and centered in the bore. Just my guess. The engine when we tore it apart had very badly worn rings. Compression and the oil rings. Burned a lot of oil too.