On July 28, 1999, at 1500 central daylight time, a Fairchild 24 C8C, N15345, piloted by an Airline Transport Pilot, sustained substantial damage during a forced landing following a loss of engine power during cruise flight, near La Fayette, Illinois. Visual meteorological conditions prevailed at the time of the accident. The personal flight was operating under the provisions of 14 CFR Part 91 and was not on a flight plan. The pilot and one passenger reported no injuries. The flight departed Hannibal Municipal Airport, Hannibal, Missouri, at 1340 and was en route to Dacy Airport, Harvard, Illinois, at the time of the accident. The pilot reported that, during cruise flight, at 3,000 feet mean sea level (msl), he noticed a substantial amount of engine oil on the right windshield. The pilot stated that, approximately one minute after noticing the oil, the engine's rpm began to drop continuously. The pilot decided to make a precautionary landing at the Kewanee Municipal Airport, Kewanee, Illinois, which was 15 nautical miles northeast of his position. The pilot reported that, approximately two minutes after he first noticed the oil on the windshield, the engine began a gradual loss of power, and he described the engine's operation as "grinding." The pilot stated that he positioned the aircraft into the wind, along Illinois State Highway 17, and executed the forced landing onto the State Highway. The pilot stated that he flared, "...as best as energy would allow and skidded 300' to [a] stop." The pilot reported that the flare, "...would not completely arrest [the] sink rate causing [the] gear to collapse." Post accident inspection of the engine revealed a crack in the head of the number two cylinder. Cylinder number two's rocker-arm cover was removed, revealing that the exhaust valve stem keeper had become unlocked, allowing the valve to drop down into the cylinder's bore. The exhaust valve stem was found to be jammed in its guide.