On December 3, 1998, at 1430 eastern standard time, a Cessna 150, N18022, collided with the ground during an emergency landing, near Columbia, North Carolina. The instructional flight was operated by the flight instructor under the provisions of Title 14 CFR Part 91 with no flight plan filed. A review of weather data from the nearest reporting facility disclosed that visual weather conditions prevailed at the time of the accident. According to the operator, the airframe sustained substantial structural damage. The certified flight instructor and the student pilot, were not injured. The local flight departed Manteo, North Carolina, at 1330. According to the flight instructor, before the initial takeoff, he and the student pilot completed a preflight inspection and a normal engine run-up. The flight instructor reported that after the initial takeoff they flew to Elizabeth City, North Carolina, where they made a touch and go landing. The flight instructor and student pilot made another touch and go landing at Edenton, North Carolina. Approximately one hour into the flight, the flight instructor reported that the engine developed a rough condition and a reduction in power. Since normal flight could not be maintained, the flight instructor selected a field that he believed would be suitable for a forced landing. During the landing roll the flight instructor attempted to avoid a collision with a drainage ditch and trees. After the airplane went through several gyrations, it rested 180 degrees from the initial landing direction. Examination of the engine disclosed that the #2 exhaust valve had failed, and pieces of the valve head were lodged in the cylinder and the exhaust system. The examination of the valve revealed that the valve head separated at the valve stem attach point. The valve stem remained in a normally installed position, and functioned when the engine drive train was rotated. A review of the engine maintenance logs disclosed that this engine had a previous exhaust valve failure 931 hours ago. The exhaust valve Part Number was SA-646612 (see attached FAA inspector's report).