[CHANMADD]

Something went down the carb or the top of the piston broke. I made a mistake once of reusing the rod, which had the big end journal slightly ovalated. I trusted the machine shop who who had promised me he had inspected the rod and I then had him assemble the short block..........
That rod broke at 5k and destroyed everything below the heads...Oh the valves also needed to be replaced. The ring gap on pistons with a high top ring land needs to be larger than the manufacturers say because the ring gets hot , expands and breaks a piece of the top land out and the result............not nice.
You gotta get all the sharp edges out of the combustion chamber to prevent future pre-ignition ,if you re-use the heads.
Good Luck...