Yeah, its definitely not piston slap because all 4 would show similar wear. The other cylinders were perfect, and had the same piston-wall clearances to within .001

So, it turns out the piston skirts melted, only on the sides , for no apparent reason other than overheating. This caused one of the wrist pin retaining clips to melt out of the piston. The actual damage was caused by melted portions of the oil rings, piston skirts, and the pulverization of one of the clips. The other clip was almost completely melted into the piston.



More pics here: http://whack.org/~dan/car/je-melted

Interesting things:
- A hole where the wrist pin clip exited the piston skirt (see pic#35 & 37)
- Rod, bearings, crank, wristpin were all totally undamaged.
- Piston-bore clearances are all still perfect
- Top fire ring is intact, still gapped at .025
- Middle (totalseal) rings were crushed together, the main one broke.
- Oil rings were totally burned up on each side, but fine in between.
- The rear thrust face before the fire ring was clean, theres no carbon deposits for about 2" ?? (see pic#31)
- The wristpin oiling grooves seem to die off on top? Don't remember if the groove is supposed to go all the way around? (See pic #57)
- I had to press out the wrist pin, it was stuck good.

- Weirdest: The thrust sides(front and back) of the skirts, as well as the rest of the piston, are more or less completely undamaged, and definitely not melted. Yet the thickest part of the piston, the wrist pin sides, are the only parts that melted... even the wrist pin insides to a slight degree. There's nothing to indicate fire was getting down past the rings on the sides at all.

I'm going to chalk it all up to simple overheating caused by the head gasket leak. The heat probably expanded the piston, and crushed the rings. It wouldn't have leaked if I had shaved off the back right head bolt 1/4" like I've told so many people. I've heard the headgasket/bolt problem had been fixed for the 1999 model year, but forgot the block I built was a *1996*. Stupid.

I would REALLY like to know why just the wrist pin ends melted so drastically though. That's weird.