Ive heard of some of those caps failing from incorrectly torqued bolts but if the piston smacked the valves somehow you should check for cracks in the piston,bent camshafts,bent valves ,stuck guides and cracks in the head. Well get this puppy runnin again.
i had the cam caps break on my motor from the aluminum water pump backing off,hiting the cover and pushing the cam through the caps. it broke the ridge off that hold the steal half circle things in