Sponsored Links (Register now to hide all advertisements)
It appears that it was seizing. Did the engine get hot? Was the piston dry when you pulled it? Did you ensure the pistons were re-installed in the same hole they came out of? Is there any metal transfer to the cylinder wall from the piston?
I can't see anything going down the spark plug hole and getting past the compression rings to do that on both sides of the skirt but who knows??