What happened
The pilot was conducting a personal flight in normal cruise configuration at an altitude of approximately 1000 feet, located about two miles southeast of the airport. During this phase of flight, the engine began to misfire, and smoke quickly filled the cabin. The pilot reported that the engine was losing power and that the aircraft could no longer maintain altitude.
Due to the deteriorating mechanical condition, the pilot elected to land in a nearby clearing rather than attempting to reach the airport. During the landing roll, the nose gear struck a small rise in the terrain and broke off. The aircraft subsequently nosed over and came to rest on its upper surface.
The investigation
A post-crash inspection revealed the root cause of the mechanical failure. The engine muffler contained several pin-sized rust holes that allowed exhaust gases to escape into the engine compartment. This hot exhaust burned through the aluminum shroud, which was not made of stainless steel, and melted the insulation on the left magneto wiring harness, voltage regulator wiring, and battery wires from the generator.
After the magneto wiring harness was replaced, an engine runup was performed with no problems noted, confirming that the electrical system functioned correctly once the damaged components were removed. The primary failure mode was identified as exhaust leakage due to corrosion in the muffler.