What was found
CRANKSHAFT BROKE AFT OF NR 2 MAIN JOURNAL AT OIL TRANSFER TUBE. PARTS SET TO TCM FOR DETERMINATION OF FAILURE. CAUSE WAS DETERMINED TO BE LOW THROUGH-BOLT TORQUE WHICH, IN TURN, CAUSED BEARING TO SHIFT AND CRANKSHAFT TO VIBRATE. AIRCRAFT HAD DEPARTED NORMALLY, WHEN LEVELLING AND SETTING CRUISE CONDITION VIBRATION WAS NOTICED. WHEN AIRCRAFT TURNED TO RETURN TO BASE, ENGINE FAILED. AIRCRAFT LANDED WITHOUT INCIDENT. (SEAPLANE). VAR TYPE CRANKSHAFT. CUT .010 INCH UNDER.