On September 1, 1998, about 1702 eastern daylight time, a Cessna 150H, N50009, registered to New Market Airport, Inc., nosed over while making a forced landing following a loss of engine power at Kill Devil Hills, North Carolina, while on a Title 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the commercial-rated pilot and one passenger received minor injuries. The flight originated from Hatteras, North Carolina, the same day, about 1615. The pilot stated he had refueled at Manteo, North Carolina, and then flew to Hatteras, which took about 45 minutes. After being on the ground at Hatteras for about 1 hour, he departed for the return trip to Manteo. As he crossed over Kill Devil Hills, he started to climb to a higher altitude to cross over the bay. About 1/4 of the way across the bay, the engine suddenly snapped and made a thud noise and then began to lose power and vibrate. He turned back toward Kill Devil Hills, and tried to make it to First Flight Airport. The aircraft would not maintain altitude and he made a forced landing in a sandy area, at which time the aircraft nosed over. Postcrash examination of the engine by an FAA inspector showed that the No. 1 cylinder exhaust valve head had broken off and caused the No. 1 piston to break and the No. 1 connecting rod to bend. Damage to the No. 1 cylinder exhaust valve prevented metallurgical examination. Logbook records showed the No. 1 cylinder exhaust valve had been installed in the cylinder during engine overhaul on April 25, 1979, at aircraft and engine total time 2324.6. The No. 1 and No. 4 cylinders were removed for repair on November 10, 1981. At the time of the accident the aircraft and engine had accumulated 1,527 flight hours since the engine overhaul and 1,236 flight hours since the No. 1 cylinder repair. (See FAA inspector statement and aircraft maintenance records attached to this report)