Introduction
A pilot reported an engine vibration and partial loss of power during the takeoff initial climb. The subsequent forced landing was made in a soft field, resulting in structural damage to the landing gear, propeller, firewall, engine mounts, and left wing.
Sequence of Events
According to the pilot, the engine issues began shortly after takeoff. Despite the partial power loss, the pilot executed a forced landing. The landing occurred in a soft field, and the aircraft sustained damage to multiple components.
Post-Accident Examination
Following the accident, FAA inspectors performed an engine test run at full power. They observed a drop of 200 RPM but could not duplicate the engine vibrations. Inspection revealed that the magneto timing was set at 27 degrees BTDC, while the specification is 25 degrees BTDC. Additionally, a carbon brush was missing from the right magneto.
The rocker arms had been installed in reverse positions on all four cylinders. The FAA inspector reported that "the exhaust valve was not receiving adequate lubrication." Physical evidence on the exhaust valve rotator caps indicated binding of the exhaust valves.
Maintenance History
The engine had accumulated 170 hours of time in service since a major engine overhaul and magneto overhaul. The pilot stated that before this accident, there had not been any previous indications of engine problems since the overhaul.
Conclusion
The investigation determined the presence of multiple mechanical anomalies, including incorrect magneto timing, a missing carbon brush, reversed rocker arm installation, and evidence of exhaust valve binding. The pilot's report indicated no prior engine issues.