What was found
THE PILOT REPORTED HEARING A LOUD POP FROM THE NR 1 ENGINE ON TAKEOFF AND A NEAR COMPLETE LOSS OF RPM. THE ENGINE WAS SUBSEQUENTLY REMOVED AND DISASSEMBLED. THE CRANKSHAFT WAS FOUND TO BE COMPLETELY BROKEN JUST IN FRONT OF THE NR 2 BEARING. WHAT REMAINED OF THE BEARING WAS FOUND IN THE OIL SUMP. THE ENGINE CASE WAS SEVERELY DAMAGED AS A RESULT OF THE BREAKAGE. A REVIEW OF THE LOGBOOKS INDICATED THAT THERE HAD BEEN TWO INSTANCES WHERE CYLINDERS HAD BEEN REPLACED. THE NR 2 AND NR 4 CYLINDERS HAD BEEN REPLACED 105 HOURS AGO AND THE NR 1 AND NR 6 CYLINDERS HAD BEEN REPLACED 221 HOURS AGO. IT IS SUSPECTED THAT THE IMPROPER TORQUEING OF THE CRANKCASE THROUGH BOLTS CAUSED THE NR 2 BEARING TO SHIFT AND CREATED A STRESS RISER ON THE CRANKSHAFT THAT LEAD TO THE FAILURE.