Accident Description
While repositioning an aircraft to its home base, the pilot experienced a loss of engine power while cruising at approximately 1000 feet above ground level. The pilot transmitted a mayday call and maneuvered the aircraft to execute a forced landing on an interstate highway. During the approach to land, the aircraft struck the top (ground) wire of a power line that crossed the highway at that location. The impact caused the aircraft to flip over and fall onto the northbound lanes of the highway.
Investigation
A teardown examination of the engine revealed that the accessory drive gear attaching bolt (part number STD-847) had backed out. This allowed the drive gear to loosen, resulting in a loss of synchronization of valve and ignition timing. Further inspection found an incorrectly sized Heli-coil installed in the crankshaft, which had been used to repair the gear attaching threads.