On September 6, 1998, at 1707 Alaska daylight time, a Cessna 140 airplane, N81045, sustained substantial damage when it nosed over during an emergency landing seven miles southeast of the Fairbanks International Airport, Fairbanks, Alaska. The private pilot owner and the sole passenger were not injured. The flight was conducted under 14 CFR Part 91 as a personal flight. The flight departed the Fairbanks/Clear Creek airstrip at 1615, and was returning to Fairbanks International Airport, from a camping trip. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The pilot told the NTSB investigator-in-charge during a telephone interview on September 6, and in his NTSB Pilot / Operator report, that while in cruise at 1,500 feet msl, he heard a "clunk" and the engine rpm began to decrease. He stated that application of carburetor heat, and changing fuel tanks did not improve the engine performance. The engine noise continued, and engine rpm continued to decrease. The pilot notified the Fairbanks Air Traffic Control Tower of his emergency, and made a forced landing on tundra. The airplane nosed over during the landing. Postaccident inspection of the Teledyne Continental Motors C-85-6-12 engine revealed the exhaust valve stem of the number two cylinder had separated, allowing the valve to be ingested into the cylinder. Metal pieces up to 1/2 inch in diameter, were recovered from the cylinder and exhaust manifold. The engine had accumulated 4,555 hours in service at the time of the accident, and 1,089 hours since overhaul.