Originally Posted by CO_VR4

Your pictures suggest to me that you dropped the head of a valve into the cylinder. Your pictures show damage to the cylinder walls which are caused by (uncompressable) foreign object(s) bouncing around in the cylinder. There is not enough room for the engine to rotate to TDC with the valve head broken off in the combustion chamber. Something has to give -- either the cylinder head and/or the top of the piston. A hundred or so revolutions with the valve head in there broke the piston, and then what was left of it caught on the lower end of the cylinder bore and the crank powered it through the side of your block. That's my guess How does the combustion chamber for that cylinder look? Beat to crap? Missing a valve head? If it is, what caused it? Could be metal fatigue, but valve float is also a common cause, when the engine is overreved and the springs are not heavy enough to maintain contact with the cam. The valves get pulled up into the head by the spring after the cam has spun away from contact, and slam into the seat. After a few of those events the spring pulls the valve stem off the head, leaving the head in the combustion chamber. Can you get pics of the cylinder head?