Hi It1s10, dozzer, r pope: I realize the oil rings have nothing to do with the test, but was wondering if oil couldn't escape fast enough behind the oil rings-which are drain back holes-if excessive oil couldn't escape fast enough and build up in the cylinder. I don't think this my trouble, just a thought. On the second rebuild all things associated with clearances, rings installed right, etc. checked out 100% (had two other motor heads there at tear down on the second rebuild so they could give me some extra eyes on the problem). Also, our machinist rechecked everything when it was re-honed. (our piston to cylinder is .0025) Between multiple people you would of thought one of us would catch a flaw. that's why this one is killing me. Although the grease may not be the problem, it'll be put together with oil this next time, and like you guys said it could be a boo boo I made, so we'll recheck everything again and find out. I'm human all the way, so when this happened the first time, I was twice as picky on the second rebuild of all clearances, etc. as one would suspect. I think your right (pope) on considering new pistons. Dozzer: our machinist wants piston in hand before he finishes the cylinder with hone machine. On second rebuild machinist measured a few cylinders with me there, plus I measured them too back at the shop. Got to go for now. thanks.