Incident Narrative
A pilot reported that during flight at 1800 feet above mean sea level, the engine seized. Subsequently, the propeller bolts sheared, and the propeller separated from the aircraft and fell to the ground. The pilot executed a landing without any damage to the airplane.
Inspection Findings
Following the incident, an inspection of the engine was conducted. A 'B' nut on the oil pressure line to the turbocharger was found loose. Cylinders in the vicinity of the 'B' nut were coated with a dark, oily substance. The turbocharger and its housing exhibited a dark, charred, oily residue.
Examination of the crankshaft revealed distress on journals number one, four, five, and six. The number one crankshaft journal displayed a blue discoloration. The number four connecting rod was broken and also colored blue. The number four cylinder head was separated from its base.
The mating surfaces of the propeller hub and the engine crankshaft flange showed areas of distress. Three of the studs that secured the propeller to the crankshaft flange had fractures that initiated on opposite sides of those studs.
Maintenance History
A top overhaul had been performed 85 tachometer hours prior to the incident.