Soaked the pistons in cleaner yesterday. Just spent my lunch hour blowing them off and scrubbing them. Looks like this motor ingested something hard at one time, maybe? Number 3 and 8 pictured here. I find it odd that it looks like the same mark, 180* from each other. No other pistons are marked. Have not looked at the heads that came off of it yet to see if it left any scars there as well. Doesn't much matter since I'm not using the original heads anyway.