HISTORY OF FLIGHT: On September 18, 1994, at 1715 central daylight time, a Piper PA-24-260, N9159P, was destroyed during a forced landing near Tennessee Colony, Texas. The private pilot and the passenger rated pilot received fatal injuries. Visual meteorological conditions prevailed for the local personal flight. During interviews witnesses reported the following information. The pilot and passenger talked of flying in the local area and practicing stalls. This was the second flight of the day and the airplane departed on runway 35 from Palestine Airport, Palestine, Texas, at 1710. The airplane was observed maneuvering at an altitude of 3,000 feet above the ground when witnesses heard a loss of engine power then an increase of engine power. They subsequently heard the engine power stop again prior to observing the airplane nose down and spinning toward the ground. One witness described the pilot as trying to "pull out of the maneuver but ran out of altitude and hit the trees and ground." Another witness described the airplane as "doing tricks" and nose down doing clockwise spins in tight rotation. The airplane then "opened up in more of a flat spin like the nose was coming up." AIRCRAFT INFORMATION: A review of the maintenance records revealed the information in this paragraph. The Engine, S/N L-4065-48, was installed in the airframe on August 2, 1985. Overhaul records for the engine showed that on March 16, 1990, 12 bolts P/N 75061 were purchased and on March 19, 1990, 6 connecting rods were purchased. This engine, at a total time of 2,320.9 hours, was removed and overhauled on July 17, 1990, and at a total time of 2,445.7 the engine was disassembled to comply with AD 91-14-22 due to a propeller strike. On the enclosed report Textron Lycoming states that "if the engine was built using the 75061 connecting rod bolts with the 74502 connecting rods then the potential for a connecting rod/connecting bolt failure exists." Engine records did not indicate any maintenance entries for the fuel divider and the AD compliance summary (copy enclosed) does not indicate AD 75-09-15 (copy enclosed) for the divider gasket. WRECKAGE AND IMPACT INFORMATION: The airplane came to rest at the base of a 70 foot tree on the edge of a creek bed with bark and branches missing from the tree trunk on the side where the airplane came to rest. Pieces of tree limbs and leaves were wedged among pieces of the left wing skin and smears similar in color to the tree limbs and bark were found on areas of the wing skin. The left wing was folded over the cockpit area and the leading edges of both wings were crushed and buckled. Flight control continuity was established. Fuel tank integrity was compromised and a portion of the right fuel tank was separated from the wing. All the spark plugs contained gaskets and were free of deposits. The safety wire and screws were removed from the fuel flow divider and the cover was lifted for examination of the fuel; however, fuel was not found in the divider and the cover was secured using 2 screws. The fuel diaphragm was not examined. The empennage area was bent and folded to the right and the cockpit area was compressed downward. One propeller blade exhibited bending and a leading edge dent. See the enclosed distribution diagram for additional details. MEDICAL AND PATHOLOGICAL INFORMATION: The Office of the Medical Examiner of Dallas, Texas, performed the autopsies. The passenger rated pilot toxicology testing indicated positive for alcohol in the blood and vitreous fluid. TEST AND RESEARCH: Textron Lycoming (report enclosed) and a Board investigator examined the engine and components at Textron Lycoming, Williamsport, Pennsylvania, on January 13, 1995. Engine continuity was confirmed. When fuel pressure was applied to the flow divider fuel "squirted from the vent hole of the top cover." The cover was removed and the fuel flow diaphragm, located against the undersurface of the cover, was found to be ruptured and was forwarded to the NTSB metallurgical laboratory for examination. They could not determine at what time the diaphragm ruptured or if it contributed to the accident scenario. Metallurgist's (report enclosed) examination revealed two tears located on diametrically opposite sides of the piston. The diaphragm was composed of 2 layers of rubber-like material sandwiched around a woven reinforcement layer. The woven material contained sets of strands oriented at 90 degrees to each other. Detailed examination of the tears revealed that both tears were parallel with one set of the strands and perpendicular to the other set of strands. The tears appeared to initiate at the edge of the end of the piston where the diaphragm was held between the piston and a backing ring. ADDITIONAL DATA: The airplane was released to the owner's representative.