What happened
At the time of takeoff, the ambient temperature was approximately 0 degrees Fahrenheit. The aircraft had been stored in an unheated hangar prior to the flight, and an oil heater had been installed on the aircraft.
During the departure phase, the oil pressure was observed within the yellow arc of the instrument. This low-pressure condition persisted throughout the duration of the flight. Although suitable airports were available for precautionary landings, the pilot continued the flight.
After approximately 30 to 45 minutes of flight time, the propeller began surging and the oil pressure decreased significantly. Within about one minute of this drop, the engine began knocking and subsequently ceased operation. The pilot then executed a forced landing.
The investigation
Post-accident inspection of the engine revealed that oil had coated the top of the engine. Despite the presence of oil on the exterior, the oil cap was found to be tightly secured, and the oil dipstick indicated approximately 4 quarts of oil remained in the system.
A detailed examination of the engine components revealed a hole in the crankcase located above the number 2 and number 4 cylinders. The investigation found that the number 2, 3, and 5 connecting rod bearings had burned and showed signs of meltdown. Additionally, the number 4 connecting rod and bearing had separated from the crankshaft, exhibiting significant heat damage and failure.
Mechanics also inspected the oil system for potential blockages. No obstructions were found within the oil passages, and the oil cooler was confirmed to be functional, as fluids flowed freely through the unit.