Got the head off finally- #4 piston has a small square notch in it facing the rear-about 1/8" wide-as well as some scratch/scuff marks on the top of the piston, so it's not shattered anyway. Bad valve adjustment? Valves look ok at first glance and there is some oily residue on the block at that piston that may indicate a bad cylinder head gasket there. I'll take some pics this weekend.