Joe, the quality of the flywheel casting comes into question, but I think there's also a possibility the flywheel retaining nut was over-tightened and the flywheel was split at the hub before it even left the factory. The radial split just propagated when the engine was run. So, the flywheel might always have been split, and the main question is whether it split because it was overtightened, or because it was a lousy casting, or both.
