Twin engine application. Blew head gasket on port engine. Replaced head gaskets and rebuilt blowers on both engines for assurance. 1st test drive, few miles, ran great. Stopped and checked for leaks etc. 2nd drive, few miles, port engine died at 5K RPM. Cam's not turning with crank. It moves a little when cranking. Broken cam or sheared timing key I guess. Anyone have this failure with this engine? Some engines are basically junk after this type of failure, piston to valve contact. How about a 575? Whatever failed in the port engine should I change in the starboard one? I did the head gaskets and blowers in the star engine because I read they were weak. They were fine when disassembled.

If it had a cast gear pressed on the cam, i bet it broke.If the engine sounds fine on the starter, then thats your problem

Take it all apart Buddy, the engine maigh move a little bit,+/- 10 degre. Some of your valve are straigh against their pistons. If you're lucky, the valves bended out of shape and maybe save the base but I wouldn't be surprised about, broken valve banging inside the cylinder destroying the piston, the head etc.etc. I'd bet that you have more than expensive looking metal filing in your oil. Even if the engine stopped within one second, the crank turned 83.33 times. I wish you good luck cos I didn't have any when it did happen to me and the engine was at around 2500rpm when it happened to me and it cost me a whole engine.