Incident Summary
Approximately one hour after departure while cruising at 5,000 feet, the pilot reported a loss of engine power. A brief application of carburetor heat temporarily restored power, but the engine soon failed again. The pilot executed a forced landing, during which the airplane collided with trees.
Engine Examination
Post-accident examination of the engine confirmed continuity of the crankshaft, camshaft, and valve train. Differential compression testing of all cylinders at 80 psi base pressure yielded readings above 70 psi. Magneto-to-engine timing was found correct. The magnetos were removed for bench testing: the right magneto operated normally, while the left magneto fired intermittently due to a partial failure of the ignition coil.
Fuel System Findings
Inspection of the fuel vent system revealed that a vented fuel cap was secured by chain to the left fuel tank filler port, and a non-vented cap was secured to the right port. The correct positions for these caps are opposite to how they were found. Additionally, a malfunction of the vent valve assembly was noted, but the assembly was not removed for further examination.
Maintenance History
The airplane had accumulated approximately 3.9 hours since its last annual inspection, which was performed on April 6, 1995.