What happened
While climbing to cruise altitude on an IFR flight plan under visual conditions, the engine lost all power approximately 10 minutes after takeoff. The pilot performed a forced landing in an open field. There were no injuries and no damage was sustained by the aircraft during the landing.
The investigation
An examination of the engine revealed that the number 2 cylinder had separated from the crankcase and become lodged within the cowl. A detailed inspection showed that the cylinder hold down studs had failed, exhibiting a 'necked-down' appearance at the fracture points. Following this failure, the rod bolts also failed, causing the piston to reverse direction and lodge itself inside the case.
Investigators found no evidence of oil starvation or heat distress. Further examination conducted at an engine overhaul facility determined that the hold down stud nuts on the remaining five cylinders did not have sufficient torque.