Accident Summary
The airplane impacted terrain during a forced landing following a loss of engine power. The pilot had recently purchased the aircraft and taken delivery on the day of the accident.
Engine Examination
Post-accident examination of the engine revealed that three of the crankshaft cluster gear bolts were fractured completely through. The fracture surface features were consistent with fatigue. Additionally, the crankshaft gear had a hole where a crankshaft dowel had been installed following a design change in 1948, as reflected in subsequent maintenance manuals. The dowel is used as a reference in machining the crankshaft.
During disassembly, the tappets fell out when the engine was overturned. It was later noted that the tappets did not contain retaining hardware. When the oil was drained, the interior of the crankcase halves contained a black colored residue.
Maintenance History
Logbook entries show that the engine was last overhauled on July 25, 1990, and had accumulated a total time since overhaul of 257.5 hours. Teledyne Continental Service Information Letter SIL98-9A, Time Between Overhaul Periods, states that engines are to be overhauled at least every twelve years.