Incident Overview
During descent through 4300 feet, the engine experienced a complete loss of power. The pilot executed an emergency landing on a golf course. However, during the landing roll, the aircraft's right wing impacted a pole, resulting in structural damage to the wing.
Post-Incident Examination
A subsequent examination of the engine identified the cause of the power loss. The 5/16 inch bolt, part number STD-847, which secured the crankshaft gear to the aft end of the crankshaft, had backed out. This allowed the gear to shift, subsequently shearing the dowel pin. With the dowel pin sheared, the crankshaft could no longer drive the accessories mounted on the engine, including the magnetos and vacuum pump. The engine had accumulated 371 hours of operation since its last overhaul.
Conclusion
The failure of the crankshaft gear retaining bolt (PN STD-847) led to the loss of engine power by disabling the accessory drive system. This necessitated the emergency landing and resulted in impact damage to the right wing.