HISTORY OF FLIGHT On March 25, 2009, about 1040 Pacific daylight time, an experimental amateur-built Reimus Sonex FR1, N1006N, collided with terrain during a forced landing near Paso Robles, California. The pilot/builder was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. The certificated sport pilot sustained serious injuries; the airplane sustained substantial damage to the firewall and right wing. The local flight departed Paso Robles Municipal Airport about 1010. Visual meteorological conditions prevailed, and no visual flight rules flight plan had been filed. The pilot reported departing Paso Robles Municipal Airport and flying for about 30 minutes when the engine began to run rough. He changed heading towards the airport in preparation for a precautionary landing, but shortly thereafter the engine lost all power. The pilot then performed a forced landing in a vineyard; during the landing the airplane struck a trellis. The airplane came to rest intact in a nose down attitude with the tail section resting on a 5-foot-tall trellis. First responders reported the presence of fuel on the ground in the area surrounding the nose of the airplane. One propeller blade was observed undamaged; the second blade was fractured midspan with aft bending of the tip. AIRCRAFT INFORMATION The two-seat, experimental amateur-built airplane was issued a Special Airworthiness Certificate on October 18, 2006. It was powered by a four-cylinder, air-cooled, AeroConversions Inc. AeroVee 2180cc engine, and equipped with a two-blade wooden propeller. AeroConversions supplied the engine to the pilot as a kit in 2005. The pilot completed the assembly of the engine later that year, 50.2 flight hours prior to the accident. According to the engine maintenance logbook, the last documented maintenance was performed on February 14, 2008, 23.42 flight hours prior to the accident. The entry, signed by the pilot, stated, "Retorqued head, valves at 0.006 gap changed oil. Reset maintenance to 25.0 hours." TESTS AND RESEARCH Post accident examination of the engine revealed that the number four cylinder head exhaust valve rocker arm adjustment nut was loose, and had rotated towards the end of its travel. Additionally, the valve clearances for the number one cylinder exhaust and intake valves, and the number four cylinder intake valves, were between 3/16 and 3/8 inches. The associated pushrods were observed loose within their cylinder heads; the pushrod for the number four exhaust valve did not make contact with the rocker arm. The AeroVee engine assembly manual recommended that the rocker arm valve clearance be set to 0.006 inches. Additionally, it stated that the torque for the rocker arm adjusting nuts be set to 14 foot-pounds. The pilot reported that he was not aware of the manufacturer’s recommendation to apply a torque of 14 foot-pounds to the rocker arm nuts during the adjustment of the valve clearance.