Accident Overview
During cruise flight, the pilot reported to air traffic control that the airplane's engine had ceased operating and declared an emergency. Subsequently, the pilot reported that there was "oil all over the windshield" and that he was attempting a forced landing. The airplane collided with trees in a densely wooded area. No witnesses to the accident were identified.
Wreckage Examination
During examination of the wreckage, oil was noted on the bottom of the fuselage, the inboard bottom skins of the left and right wings, and the tail surfaces. The #2 cylinder was found separated from the engine. Examination of the engine revealed that all 8 of the fasteners (6 studs and 2 through bolts) securing the #2 cylinder to the crankcase were separated. Fretting was noted on the mating surfaces of the cylinder base flange and the crankcase deck (flat face around the cylinder bore) and on the mating surfaces of the crankcase halves.
Metallurgical Analysis
Metallurgical examination of the 8 fasteners indicated they all separated due to fatigue cracking probably due to insufficient clamping force. Insufficient clamping force can result from improper torque application at cylinder installation or from the clamped surfaces moving closer over time. Fracture of the studs led to separation of the #2 cylinder from the crankcase and a loss of engine power.
Maintenance History
Examination of the maintenance records showed that the engine had accumulated about 839 hours since a major overhaul approximately 13 years prior to the accident. There were no entries in the records indicating removal of the #2 cylinder since the major overhaul.