Incident Description
The pilot reported hearing a loud noise accompanied by a sudden loss of engine power. In response, a forced landing was performed in a field. No further details about the flight or landing were provided.
Post-Accident Inspection
Following the incident, an examination of the engine revealed two holes in the top of the engine crankcase. The number 3 piston, along with its connecting rod and bolts, were removed for detailed analysis. One of the connecting rod bolts was found to contain microfissures typical of fatigue cracking on the head portion of the bolt.
Fatigue Crack Characteristics
The fatigue cracking had initiated from multiple locations on one side of the underhead radius. The crack had propagated nearly all the way through the cross section of the bolt before the final separation occurred. This mode of failure is consistent with progressive stress cycling leading to material degradation.
Maintenance History
A review of the airplane engine logbooks showed that the last major overhaul was conducted on March 3, 1965. No other maintenance records or operational history were specified.