Incident Overview
An aircraft in level cruise at 6,500 feet msl experienced a sudden engine failure without warning. The pilot heard a 'pop' from the engine compartment coincident with the power loss. Despite switching fuel tanks and activating the electric boost pump, which restored fuel flow on the gauge, the engine did not restart. The pilot selected an open field and continued restart attempts while preparing for an off-airport landing. The aircraft touched down in the field and rolled some distance before the nose gear collapsed.
Post-Accident Examination
During a teardown inspection of the engine, all cylinder bases and through bolt studs exhibited evidence of oil leakage. When the cylinders were removed, all through bolt and cylinder hold down stud nuts were loose enough to break torque with one hand using a short open-end wrench. Removal of the cylinders revealed fretted cylinder bases and pads. Separating the case halves revealed fretting on all cylinder pads and bearing saddle-parting surfaces, with more pronounced fretting on the No. 2 main bearing saddle surfaces. The No. 2 main bearing was fragmented and found in the oil sump, with erosion and smearing evident on the bearing saddle. The crankshaft was fractured across the No. 3 short cheek, with heavy scoring on the Nos. 2 and 3 main journals.
Maintenance History
Review of the maintenance records disclosed that cylinders 1, 2, 4, 5, and 6 were replaced on March 24, 1997, 232 hours prior to the incident.
Conclusion
The investigation identified extensive mechanical issues within the engine, including loose fasteners, fretting, bearing fragmentation, and crankshaft fracture. No probable cause was stated in the source.