ATL94LA150

The flight instructor and his student were taking off on a local, instructional flight. About 300 feet AGL, during the initial climb, the engine lost power, accompanied by a strong vibration. The aircraft was force landed, and collided with trees. A post- accident examination of the engine revealed that the number 2 exhaust valve was stuck open. Further inspection showed coking and carbon deposits on the valve stem and guide. After cleaning, the valve stem diameter was measured to be .4328'. The allowable range is .4335' to .4340'. The engine had a history of sticking valves; the number two exhaust valve was freed by maintenance personnel 5 hours before the crash. They also reported that the valve was freed without removing the cylinder or the valve.

On August 3, 1994, at 1425 eastern daylight time, a Cessna 150J, N60182, collided with trees and terrain during takeoff from the JAARS-Townsend Airport in Waxhaw, North Carolina. The aircraft was destroyed, while the commercial-rated flight instructor and his student were not injured. The aircraft was operated under 14 CFR Part 91 by Waxhaw Aero Club. Visual meteorological conditions existed at the time, and no flight plan was filed for the local, instructional flight. The flight was originating at the time of the accident.

The flight instructor reported that as the aircraft climbed through about 300 feet above ground level, the engine lost power, accompanied by a strong vibration. Unable to land on the runway, he force landed the airplane straight ahead. During the landing, the airplane collided with trees, and came to rest, inverted.

After the accident, the engine was removed from the accident site and transported to a maintenance facility, where an examination of the engine was performed. The number 2 cylinder valve cover was removed, and the exhaust valve was found to be stuck in the full open position. The number two cylinder head was then removed and inspected. There was no evidence of damage found to the head or to the top of the piston. The exhaust valve was removed from the valve guide; there were carbon deposits and evidence of coking from excessive oil on the valve stem and on the inside of the valve guide. The valve stem was cleaned, and the stem diameter was found to be .4328 inches. The overhaul manual for the engine specifies that the allowable range for the stem diameter is a minimum of .4335 inches, and a maximum of .4340 inches. The coating on the inside of the valve guide was then cleaned with a homing tool, and an additional .0020 inches of clearance was added with one scrape to the guide.

The local mechanic reported that N60182 was examined for a rough running engine, in his maintenance shop, about 5 hours prior to the accident flight. No compression was observed on the number 2 cylinder. The exhaust valve was stuck, and was freed without removal of the cylinder or valve. The engine was then run on the ground. The engine ran smoothly, and developed normal power. The aircraft was then released for flight.

According to the engine logbook, on June 28, 1994, the number 4 cylinder was removed to correct a stuck exhaust valve. The valve guide was reamed, and the cylinder was reinstalled. A subsequent ground and flight check of the aircraft was satisfactory.

According to logbook entries, the engine had been operated about 420 hours since the last major overhaul. The details of that overhaul were not located. The operator did not comply with 49 CFR Part 830, requiring the completion of an NTSB Form 6120.1/2 (Pilot/Operator Report).