On June 26, 2003, about 1430 eastern daylight time, a Cessna 150F, N8517G, was substantially damaged during a forced landing after experiencing a partial loss of engine power near Williamson, New York. The certified flight instructor (CFI) and student pilot were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the local instructional flight conducted under 14 CFR Part 91. According to the pilot, the flight had departed the Williamson-Sodus Airport (3G7) in Williamson, about 1330, and remained in the traffic pattern with the student pilot at the controls. After conducting a fourth touch-and-go, as the airplane was climbing, the engine began to run rough. The CFI took the controls and elected to perform a forced landing to an apple orchard. During the forced landing, the left and right wings struck trees. The airplane came to rest upright. A Federal Aviation Administration (FAA) inspector examined the airplane after the accident and observed substantial damage to both wings. The inspector also noted that when the engine was rotated using the propeller blades, the number one cylinder did not develop compression. The valve box cover was removed, and a fractured cylinder rocker shaft boss was observed. The inspector added that the fracture on the boss was consistent with fatigue. Airworthiness Directive (AD) 94-05-05 R1, published in 1994, was issued to prevent possible engine power loss and subsequent engine failure. The AD required that maintenance personnel inspect the cylinder rocker shaft bosses for cracks at the next cylinder removal from the engine or engine overhaul, whichever occurs first, after the effective date of the AD. A revised AD became effective in 1996. Review of the airplane's engine maintenance records indicated that the last engine overhaul and cylinder removal was accomplished in 1977. The engine had accumulated about 2,003 hours of operation since it's manufacture in 1966, and about 700 hours of operation since the overhaul. An annual inspection of the airframe and engine was performed during September 2002.