Incident Overview
During cruise flight, the pilot experienced a catastrophic engine failure and subsequently performed a forced landing to an airport. The landing was successfully executed without further incident.
Engine Examination
Post-incident examination of the engine revealed a three-inch hole in the engine case adjacent to the number 2 cylinder. A teardown of the engine showed a separated number 2 connecting rod and significant damage to the number 2 piston and cylinder. Heavy longitudinal scoring and metal transfer were observed on the number 2 cylinder bore, and the inboard edge of the barrel was deformed, consistent with connecting rod contact. The inboard end of the number 2 connecting rod was fractured in two locations adjacent to the rod bearing area, with surrounding discoloration consistent with extreme localized heating. A connecting rod bolt fragment exhibited tensile elongation and surface and fracture features consistent with an elevated temperature overstress separation.
Piston and Cylinder History
The aircraft had been operated for about four hours since the number 1 and 2 cylinder and piston assemblies were replaced by a maintenance facility in Knoxville, Tennessee. The crowns of both pistons indicated they were manufactured by Superior Air Parts and were 0.010-inch oversize (P010) in diameter. However, diameter measurements at various datum points revealed that the number 2 piston was closer in size to a standard size piston and did not contain any measurable dimensions within the P010 limits. The number 1 piston measurements tended to be closer to the P010 dimensions, with two locations within the P010 limits. Hardness measurements from both pistons were below the specified range for a new piston.
Maintenance Details
The cylinder assemblies were supplied by an aviation facility in El Reno, Oklahoma, which used "serviceable parts." The specific service history of the pistons and piston pins could not be determined. The owner of the aviation facility stated that they did not check the "piston skirt clearance" and expected the installer to check the skirt clearance per the Teledyne Continental Motors (TCM) Overhaul Manual at the time of installation. According to the maintenance facility in Tennessee, the cylinders were installed per the TCM Overhaul Manual.
Conclusion
The investigation documented the physical evidence of engine component failures and the maintenance background, but did not identify a single probable cause for the failure.