On April 7, 1999, at 1045 central daylight time, a Cessna 172N, single engine airplane, N5171K, impacted terrain during a forced landing following a loss of engine power while maneuvering at low altitude near Turrell, Arkansas. The airplane was operated by Downtown Aviation, LLC, Memphis, Tennessee, under Code of Federal Regulations (CFR) Part 91. The commercial pilot/flight instructor and the student pilot were not injured. The airplane sustained substantial damage. Visual meteorological conditions prevailed and a flight plan was not filed for the local instructional flight. The flight departed Memphis, Tennessee, at 1000. During interviews, conducted by the FAA inspector, and on the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), the operator and the pilot reported that the student was performing ground reference maneuvers at 1,200 feet msl when the flight instructor noticed a "bad vibration coming from the engine." The flight instructor performed the emergency procedures and diverted to an agricultural airstrip (approximately 12 miles west/southwest of the departure airport. Upon aligning the airplane with the runway to the north, he noticed a "strong tailwind" and observed 2 agricultural airplanes at the departure end of the runway. At this point, the engine produced partial power and he circled the airstrip for landing to the south on a dirt road (rough/uneven) that paralleled the airstrip. Prior to the touchdown, there was a total loss of engine power. The instructor stated that he prepared his student for a hard landing. Upon landing, the airplane "bounced and a gust of wind from the southeast blew the right main tire into the muddy ditch." Subsequently, the airplane rolled into an adjacent field, the nose gear sank into the soft dirt, and the airplane nosed down. The outboard left wing struck the ground before the airplane came to rest on the main landing gear. The pilot reported the winds were from the south southeast at 10 to 15 knots. The National Weather Service (NWS) surface observation at Memphis, Tennessee, was reporting the winds from 150 degrees at 8 knots. The operator and the FAA inspector examined the aircraft and found that the rear spar of the left wing was buckled outboard of the fuel tank. The FAA inspector found that the "number one cylinder intake valve rocker assembly stud bolt was backed out of the hole four turns, allowing the valve to become inoperative." See the enclosed inspector's report for additional details. A Textron Lycoming Service Bulletin (SB 412B) was issued on March 10, 1978, for replacing all rocker arm retaining studs with oversized studs. This O-320-H2AD, serial number L-7296-76 was shipped from the factory on October 12, 1979; therefore, according to the manufacturer representative, the SB would have been complied with by the manufacturer. The original logbooks were reported lost; therefore, the complete history of the engine, since shipment from the factory, could not be verified. A review of the reconstructed logbooks revealed that on February 12, 1998, the engine had accumulated "200 to 300 hours" since major overhaul. A 100-hour inspection maintenance entry for September 24, 1998, stated in part: "Removed #1 cylinder, honed and installed new rings. #1 cylinder compression checked 68/80 at ground run. This engine determined to be in an airworthy condition." The last 100 hour inspection was performed on March 9, 1999, at an accumulated aircraft time of 8,019.1 hours. The airplane was released to the owner on May 5, 1999.