19990625007629A

Acft experienced an unknown emergency, made an emergency landing near osborne and norris streets, and sustained substantial damage on landing, other circumstances are unknown. (.4)the experimental helicopter experienced a loss of engine power in the takeoff initial climb, about 450 feet AGL, and the pilot autorotated to a hard landing on a city street. A witness who saw the helicopter hovering before takeoff said that the engine 'missed' twice before the helicopter took off. After the helicopter took off and was about 80 to 90 feet AGL, he heard the engine make a 'sputtering' or 'popping' noise. This flight was the first test flight after building the helicopter and the pilot had completed 4.3 hours of engine run-ups and hover time. Examination of the engine found that the no. 3 cylinder intake valve stem cap was damaged and the rocker arm was loose. The valve lash clearances on the other three cylinders were found to be from 0.006 to 0.022 inches greater than the manufacturer's specifications. No other damage was noted to the engine or valve train. The no. 3 cylinder intake valve stem cap was replaced and the other valve clea rances set to the proper 0.004-inch specification. The engine was then installed in a test cell and performed normally during all operational tests. The rotorway engine maual instructs owners to measure and adjust the valve lash, and states, 'if any adjustment is necessary at one hour, valve adjustment should be repeated hourly until the lash stabilizes.' The pilot reported that he had made a total of four adjustments during the first inspection, but after that, all measurements had been within the manufacturer's specifications.