most probably because of the mechanical failure. n yes it maybe from the bearing clearance.. i also believe there is physical contact between head n piston that causing the piston to crack into thousand pieces...but when u open the engine, the piston was hit top or ur head cause 1 of ur piston crack totally
so next time have to be careful when rebuilt ur b20b
the lesson is do not rush when building up an engine especially hybrid one...
and one more thing maybe i'm suite to 1.6 only laaa...