Accident Overview
Approximately six operating hours prior to the accident, the engine had been overhauled and modified with a new type of camshaft under the provisions of a Supplemental Type Certificate. During a level cruise, the pilot reported hearing a loud bang emanating from the engine, concurrent with the engine stopping.
On-Site Inspection
Initial inspection of the aircraft by FAA inspectors revealed that oil covered the windshield. The number two cylinder rod was observed protruding from a hole in the top of the engine case. One counterweight assembly was found missing from the crankshaft counterweight blade. The missing counterweight, along with cover plates, retaining cir-clips, and associated bushings, were recovered from the oil pan.
Examination and Findings
Optical examination of the recovered pieces showed that the retaining cir-clip had failed. This failure allowed the counterweight pin and the weight itself to separate from the crankshaft. The inspector determined that the cir-clip had been installed backwards, leading to its failure.
Conclusion
No further information about the aircraft, pilot, or circumstances was provided. The investigation focused solely on the mechanical failure of the cir-clip and the resulting engine damage.