Originally posted by: Doctorturbo
This whole deal could be caused by many, many things. If you did not do anything stupid like rap it out on an ice cold engine or run it low on oil the most likely cause will be a tight wrist pin when they put it together.
If they got the wrist pin a little tight to begin with it will gall some and get hot; which will cause it to gall some more and on and on.............until up locks up or scuffs the **** out of the piston.
It should not make any difference but like the cam, the piston pin is splashed oiled. In my opinion you are doing it an injustice by breaking it in slow. The more oil you can get splashed on the pin the better. (Higher RPM) That's one of the reasons why cam makers don't want you to idle a new cam.
Detonation could also cause this. How much compression did they set it at and what kind of fuel did you run in it? There is not many things other than detonation that will cause a crack in a piston top.