This VH4D Wisconsin was made in 1985. This engine is all original. After using it for about 4 hrs recently with no problem or indication of anything going wrong, i was finished my work and turned it off. The next day I started it and it sounded like an old steam jenny. It was huffing, puffing and blowing air pressure out of several places of the head gasket. So I knew instantly that the head gasket had blown. I went ahead and pulled the head off and guess what I find? A hole about the size of a quarter in the top of one of the pistons. In fact, it looked like the piston came up, hit a rock, and busted a hole in the top. These are not light weight components. I am going on replacing the piston and head gasket and whatever else I need to do for repair. And double and triple check everything in that engine. My question is simple, does anyone have any idea what would have caused this??