Incident Overview
During cruise flight at 2,300 feet, the pilot was reviewing a map when he heard a noise and noted a change in engine sound. Observing slow rotation of the propeller blades and the tachometer dropping to zero, he declared an emergency on guard frequency and initiated a forced landing. Spotting a golf course, he initially headed toward it but determined that golfers would obstruct the approach, so he redirected toward a road. During the landing rollout, the left wing struck a sign.
Post-Accident Examination
Examination of the engine assembly revealed severe fretting on the crankcase center web mating surface. The crankshaft center main bearing was found displaced aft at the same location, with the bearing halves partially rotated out of their normal position. This displaced bearing blocked the oil supply hole that provides lubrication to the No. 3 connecting rod, leading to failure of that connecting rod due to oil starvation.
Maintenance History
Review of the aircraft logbooks showed that the engine had exceeded the manufacturer's recommended time before overhaul.