Event
After takeoff and the first power reduction, the pilot reported a loud bang from the engine. The tachometer indicated zero RPM, although the propeller continued rotating. Unable to return to the departure point, the pilot performed a ditching. All occupants evacuated the aircraft without injury. No preflight discrepancies were noted, and the oil capacity was 9 quarts. There were no reported engine malfunctions during start, taxi, or run-up before takeoff.
Examination
Disassembly of the engine revealed that the crankshaft was fractured at the No. 3 crankshaft cheek. Metallurgical examination determined the fracture was due to fatigue. The No. 2 main bearing was missing from its position in the crankcases; pieces of the bearing were found in the oil sump. Additionally, the bolt for the No. 2 cylinder connecting rod was fractured near the bolt head. Metallurgical analysis of the bearing pieces and the fractured connecting rod bolt showed overstress on the undamaged fracture surfaces and features consistent with bending shear separation, respectively.
Examination of the crankcase halves revealed brown to black deposits at all cylinder mounting surfaces, consistent with corrosion and fretting products. Fretting and polishing were noted in several areas of both crankcase halves. The No. 2 main bearing saddle area was described as "severely damaged with large rolled edges formed at the forward and rear edges."
Maintenance History
The engine was rebuilt by Teledyne Continental Motors on August 23, 1988, and installed in the airplane on October 1, 1988. All cylinders were overhauled and installed on the engine on November 25, 1994. At that time, the engine had accumulated approximately 986 hours since major overhaul. Between October 1, 1988, and November 25, 1994, ten oil samples were taken for analysis, but the reports were not located in the maintenance records and were unavailable from the facility that performed the analysis. There was no record of repair or replacement of the No. 2 or No. 3 cylinders between the installation of the overhauled cylinders in 1994 and the last logbook entry dated March 6, 2001. At the time of the accident, the engine had accumulated about 548 hours since the overhauled cylinders were installed.