[Big-Foot]

I agree to the detonation... Also - Check the inside of your intake manifold for the chunk of piston.. Wouldn't be the first time that a new engine ingested a piece of the old engine.. Judging by the oily carbon deposits on the other pistons - she was pumping just a bit of oil. That will help promote detonation as well.. The clean piston is odd unless it got a good steam cleaning from the leaking headgasket..