On March 1, 1996, about 1515 eastern standard time, a Bell 206L4, N6248X, registered to the Bell Helicopter Textron, Inc., experienced total loss of engine power during cruise flight and was substantially damaged during an autorotative landing near Chiefland, Florida. Visual meteorological conditions (VMC) prevailed at the time and no flight plan was filed for the 14 CFR Part 91 business flight. The commercial-rated pilot, the sole occupant, was not injured. The flight originated about 1300 central standard time from the Marianna Municipal Airport, Marianna, Florida. The pilot stated that during cruise flight about 400 feet mean sea level, in VMC, he first heard the engine decelerate then heard the engine out audio announcement. He verified that the throttle was full open then lowered the collective control for an autorotative landing. He observed a clearing and initiated a 180-degree turn but when the flight was near the ground, he observed uneven terrain and elected to zero his forward speed. The helicopter then landed hard and rocked forward, causing the main rotor blades to contact the tailboom. The helicopter had been operated for about 1.3 hours since fueling and a total of 74.8 hours since manufacture. Postaccident examination of the helicopter by an FAA airworthiness inspector revealed sufficient fuel to sustain engine operation. Visual examination of a sample of fuel obtained from the fuel tank revealed no evidence of contamination. The helicopter was recovered and the engine was started and operated several times using the fuel supply in the fuel tank with no discrepancies noted. Vacuum test of the fuel system revealed no evidence of preimpact failure or malfunction. The engine was removed from the helicopter for further tests. The engine was placed in a test stand at the manufacturer's facility and operated with no discrepancies noted. The engine-driven fuel pump with attached main fuel control and the power turbine governor (PTG) were removed and sent to the manufacturer's facility for bench tests which revealed no failure or malfunction that would have prevented normal engine operation. The only discrepancy noted was a sheared PTG throttle lever stop roll pin. According to Allied Signal personnel, failure of the roll pin has previously been determined to occur due to over torque of the outer lever attachment nut. The failure did not affect operation of the throttle input from the cockpit. Review of the helicopter historical records revealed that the power turbine governor was installed on 12/15/95, and had accumulated 70.5 hours since new.