What was found
INCORRECT CYLINDER BASE O-RINGS INSTALLED AT TOP-OVERHAUL. THE O-RINGS INSTALLED APPEARED TO BE THE SIZE FOR THE ENGINE. THESE LARGER CROSS SECTION SEALS WERE PINCHED BETWEEN THE CYLINDER BASE AND THE CRANKCASE. THIS RESULTED IN A LOW THROUGH-BOLT TORQUE. NUMBERS 2 AND 3 MAIN BEARINGS SPUN, DISRUPTING OIL FLOW TO THE NUMBER 4 CONNECTING ROD. THE NUMBER 4 CONNECTING ROD FAILED AND PENETRATED THE CASE.