Incident Report
The pilot reported that while in cruise flight, the engine began running rough and losing power. Smoke entered the cockpit, and a clanking noise was heard from the engine. The pilot decided to perform a forced landing on I-20 West. However, the pilot forgot to extend the landing gear, and the aircraft touched down on the guard railing separating the eastbound and westbound lanes. The fuselage and wings sustained substantial damage.
Engine Examination
The engine was removed and sent to Textron Lycoming for further examination. Inspection of the bottom number one and number four spark plugs revealed oil and heavy carbon debris. Heavy carbon debris was also found in the exhaust valve guide area.
The number four exhaust valve was stuck in the open position. The tip of the number four exhaust valve showed damage signatures consistent with operation 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 to be straight when placed on an optical comparator in the Lycoming Metrology laboratory.
The number four piston dome displayed a circular signature consistent with an impact mark from the exhaust valve. The number four cylinder exhaust push rod and shroud tube were found broken and separated from the engine as received. Additionally, the number four cylinder exhaust hydraulic lifter was found to be below leak down specification minimums.