We have had a 454 engine rebuilt 4 times and each time after approximately 1000 miles, the cam fails. We have made sure to break the engine in properly, not to overrev, etc. etc. and each time the cam fails. This time after about 1200 miles, went to start and getting a popping sound. In times before, it would be under load before it started this, now it was just warming up. Anyone experience anything like this?