What happened
The pilot reported hearing a loud noise followed immediately by a loss of engine power. In response to the engine failure, the pilot executed a forced landing into a nearby field.
The investigation
Post-accident inspection of the engine identified two holes located in the top of the engine crankcase. Investigators removed and examined the number 3 piston, along with its connecting rod and bolts.
Examination of one connecting rod bolt revealed microfissures consistent with fatigue cracking on the head portion of the bolt. The investigation determined that the fatigue cracking started at multiple locations on one side of the underhead radius and progressed through nearly the entire cross section of the bolt prior to final separation. A review of the airplane engine logbooks showed that the most recent major overhaul had been completed on March 3, 1965.