On September 19, 2012, about 1045 central standard time, a Hiller UH-12B helicopter, N94735, experienced a loss of engine power while maneuvering at low altitude near Rio Vista, Texas. The student rated pilot, sole occupant, was not injured during forced landing and the helicopter was substantially damaged. The helicopter was owned and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Day visual meteorological conditions prevailed for the flight, which operated without a flight plan. The pilot reported that he was on a survey flight, looking at cattle and fences from the helicopter. He stated that the helicopter engine suddenly stopped, so he elected to autorotate to the field. The helicopter made a hard landing and the skids were caught by the high vegetation. An examination, by the responding Federal Aviation Administration (FAA) inspectors revealed that the helicopter’s, tailrotor and aft section of the tailboom had separated from the helicopter. The main rotor blade had damage consistent with impacting the tailboom. The engine was examined by an Airframe and Powerplant (A&P) mechanic, under the supervision of the FAA inspectors. The mechanic found no compression on the number five and number six cylinders; neither valve moved on the number six cylinder and only the intake on the five cylinder moved. The number six cylinder was removed and revealed damage to the crankcase and camshaft boss. Additionally, the number six connecting rod, piston pin, and plugs were found intact; however, the number six piston was missing; several pieces of metal were located in the engine.