On September 10, 2002, at 1930 central daylight time a Piper PA24-250, N5724P, registered to a private individual and operated by the private pilot, collided with a guard rail while making a forced landing following a loss of engine power on Interstate I-20 near Morton, Mississippi. The flight was operated under the provisions of Title 14 CFR Part 91, and visual flight rules. Visual meteorological conditions prevailed and no flight plan was filed. The pilot was not injured and the airplane sustained substantial damage. This leg of the flight originated in Tuskegee, Alabama, on September 10, 2002 at 1800. According to the pilot, while in cruise flight, the engine started running rough and loosing power. Smoke was entering the cockpit and a clanking noise could be heard coming from the engine. The pilot elected to make a forced landing on I-20 West. The pilot forgot to put the gear down and landed on the I-20 guard railing separating the east and west bound lanes substantially damaging the fuselage and wings. The engine was removed and sent to Textron Lycoming for further examination. On March 17, 2003, the engine was examined by Lycoming personnel with an NTSB representative present. Examination of the engine's log book revealed that the engine was shipped as a new O-540-A1C5 model from Lycoming Engines, Williamsport, Pennsylvania to Aero Design and Engineering Co. on July 18, 1958. The engine was returned to the Lycoming factory, rebuilt, and shipped to Santa Monica Aviation on June 30, 1962. On July 26, 1968 a new nameplate was furnished to T.W. Smith Aircraft. The engine was not returned to Lycoming until after the mishap on February 19, 2003. Review of the engine logbooks showed 979 hours since the last major overhaul. The time between overhaul (TBO) on this engine is 2000 hours. The engine log excerpts did not reveal compliance with Lycoming Service Bulletin 388, procedure to determine exhaust valve and guide condition. The service bulletin recommends the valve guide to be checked every 400 hours. Examination of the bottom number one and number four spark plugs revealed oil and heavy carbon debris. Cylinders number one, three, five, and six were not removed during the examination. The number two cylinder and piston was removed to facilitate removal of the number four cylinder and piston. The number four exhaust valve was not a Lycoming part. Heavy carbon debris was found in the valve guide area. The number four exhaust valve was stuck in the open position. The number four exhaust valve tip end had damage signatures consistent with operating without the rotator cap. The rotator cap was located at the bottom of the number four rocker cover. The number four exhaust valve stem was observed straight when placed on the optical comparator in the Lycoming Metrology laboratory. The number four piston dome had a circular signature consistent with an impact mark from the exhaust valve. The number four cylinder exhaust push rod and shroud tube was broken separated from the engine as received. The number four cylinder exhaust hydraulic lifter was found below leak down specification minimums.