NTSB Identification: DEN04LA136.
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Accident occurred Monday, September 06, 2004 in Gillette, WY
Probable Cause Approval Date: 07/07/2005
Aircraft: Cessna 182, registration: N2725G
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot stated he was in cruise flight when the engine began to run rough. He heard sounds of grinding metal and shortly thereafter, the "engine began to shake violently." The pilot shut the engine down and attempted a forced landing to a plowed field. During the forced landing, the nose wheel impacted a small rut, separating the nose landing gear tire from the nose landing gear assembly. The airplane nosed over, causing substantial damage. An internal examination of the engine showed the number 3 piston, piston rings, and tension springs, and the number 3 exhaust valve head had fragmented into numerous pieces. These pieces were located in the oil sump. The inside of the crankcase halves showed impact damage in the areas aft of the number 4 piston and forward of the number 3 piston. The top inside of the number 3 cylinder head showed numerous impact marks including a 7/8 inch long, 1/8 inch wide and 1/8 inch deep indentation at one of the spark plug openings, and a 1/2 inch long, 1/8 inch wide, and 1/8 inch deep indentation at the area of the exhaust valve seat which were consistent with a valve head edge impact. The number 3 exhaust valve seat was not present. The number 3 exhaust valve stem was removed and examined. Fractures observed on the valve stem were consistent with an overload failure. The number 3 exhaust valve guide showed elongating distortion. An examination of the crankshaft, camshaft, other cylinders, pistons, valves, and valve springs showed no pre-existing failures. No evidence of the number 3 exhaust valve seat was found among the fractured pieces in the engine. An examination of the remaining airplane systems revealed no anomalies.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

improper engine overhaul performed by the mechanic which resulted in the fractured exhaust valve and subsequent partial loss of engine power. Contributing to the accident was the lack of suitable terrain for a forced landing.

Full narrative available

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