Event Description
According to the pilot, while cruising at an altitude of 5,000 feet MSL, he noticed the smell of burning oil. Shortly thereafter, the engine RPM began to decrease, and the oil pressure dropped toward zero. A subsequent 'explosion' was heard, and the engine seized. The pilot executed a forced landing, during which the airplane impacted trees and came to rest on the ground in a left wing down attitude.
Engine Examination
Post-accident examination of the engine revealed a three-inch diameter hole in the crankcase above the number 3 cylinder attach point. The number 3 connecting rod was found separated. During engine disassembly, one of the connecting rod cap bolts for the number 3 cylinder was found destroyed. One of the nuts for the number 3 connecting rod cap was found lying inside the piston skirt, having separated from its bolt. The exterior of this nut and its threads appeared undamaged to the naked eye. No loose cotter pins were found within the engine. All other connecting rod cap bolts were found attached and secured with cotter pins.
Additional Findings
The end cap of the number 2 piston pin was missing. The inner surface of the number 2 cylinder barrel exhibited longitudinal scoring in the direction of piston action, corresponding to the diameter of the piston pin.
Maintenance History
One day prior to the accident, an oil change was performed, and metal particles were found on the oil screen.