What happened
During the cruise phase of flight, the aircraft experienced a loss of engine power. The pilot was forced to perform a landing in a rough, plowed field. The impact resulted in damage to the aircraft.
The investigation
An examination of the engine identified that the anti-rotation pin for the crankshaft gear had sheared and the crankshaft gear retaining bolt was missing. Investigators searched the engine oil pan but did not find the bolt, nor was the crankshaft gear retaining bolt located anywhere within the engine.
A review of maintenance records showed that the engine had been last overhauled on April 6, 1986, and had recorded 522 hours of time in service since that overhaul. There were no subsequent logbook entries indicating that the crankshaft gear or the retaining bolt had been removed.