On September 1, 2020, at 1100 eastern daylight time, a Stinson 108-3, N909C, was substantially damaged when it was involved in an accident near Coleman, Michigan. The pilot was uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that the airplane had been flying for about 45 minutes before it experienced a total loss of engine power. The pilot then performed a forced landing to a soybean field, where it rolled for about 180 ft and nosed over resulting in substantial damage to the fuselage and empennage. Postaccident examination of the engine, by a Federal Aviation Administration representative, revealed the single generator drive gear for the ignition system had separated into several pieces. The drive gear shaft installation called for a castellated nut with a cotter pin to retain the drive gear, but the cotter pin had not been installed and allowed the nut to back off. The generator was installed by the pilot, who did not hold a mechanic certificate, during his overhaul of the engine. The pilot stated that he performed the overhaul of the engine and installation of the generator under the supervision of a mechanic with an airframe and powerplant ratings. No other mechanical anomalies with the engine were noted.