Accident Overview
A pilot executed a forced landing following an in-flight engine failure. The aircraft landed without further incident, and subsequent investigation focused on determining the cause of the power loss.
Teardown Examination
Engine teardown revealed multiple mechanical anomalies. The No. 4 exhaust valve head had separated from its stem. Metal debris was found in the oil sump, indicating internal component failure. Additionally, the No. 1 connecting rod was separated from the crankshaft. Examination of the area around the No. 1 connecting rod crankshaft journal showed evidence of improper lubrication.
Engine Component Findings
The oil pump was intact and an adequate supply of lubricating oil was available, suggesting the lubrication issue was localized rather than systemic. Prior to the valve head passing through the piston top, it made numerous dents and abrasions on the piston head and cylinder dome. The resulting sandblasting effect obliterated the fracture surfaces, hindering metallurgical analysis of the initial failure point.
The sequence of events likely began with the exhaust valve head separation. The liberated valve head caused damage to the piston and cylinder, generating debris that contaminated the oil system. The connecting rod separation may have been a secondary consequence of the debris or the resulting mechanical disruption.