[olddog]

I didn't realize the engine had 10K miles. I doubt it had anything to do with assembly fit.

The piston could have been leaned out long ago and caused a crack. Many other possibilities, as well (bad piston as others have said).

I do not think an over rev or any other driving issue would cause this. I doubt the previous owner new anything was wrong. A failure like this goes un-noticed until a chunck comes loose.

Sorry about your luck. Hope you end up happier with a better engine when your done. You will get a lot of personal satifaction from helping to design what goes into it and knowing what is in it.