What happened
The pilot was conducting a flight following the recent installation of two magnetos. During the climb out, the engine failed. Both the pilot and a witness reported that the engine quit during this phase of flight, with the pilot noting that he heard something break inside the engine.
In response to the engine failure, the pilot attempted an emergency landing on a gravel driveway located south of the runway. Upon impact with the ground, the main landing gear collapsed. The aircraft subsequently slid for 150 feet before coming to a rest. The pilot was not injured.
The investigation
A post-accident inspection of the engine and components revealed that both magnetos had been installed without cotter pins on the drive gear retaining nuts. This improper installation allowed the nuts to back off, which disconnected the magnetos. Furthermore, one of the gears fell into the engine, causing the reported engine stoppage.