Incident Overview
During cruise flight, the airplane experienced a loss of engine power, necessitating a forced landing in a rough plowed field. The aircraft sustained damage during the landing.
Engine Examination
Post-incident examination of the engine revealed that the crankshaft gear retaining bolt was missing. Additionally, the gear's anti-rotation pin was found to be sheared. Inspection of the oil pan did not yield the missing bolt, and no retaining bolt was located within the engine.
Maintenance Records Review
A review of the maintenance records indicated that the engine was last overhauled on April 6, 1986. Since that overhaul, the engine had accumulated 522 hours of time in service. No subsequent logbook entries were found that documented any removal of the crankshaft gear or its retaining bolt.