I have two new 350 crate engines I just installed in my boat last year. I have 19 total running hours. Only two from this year before suddenly losing an engine the other day running at 3300 rpms. #6 piston has a hole in it and everything else is like new. no damage to the head, all carburetor screws intact, valves look great. The engine was running great and timing was set correctly. Has anyone else seen this? Any guesses what might cause this?