On November 20, 2006, at 1238 Pacific standard time, a Stinson 108-1 airplane, N97949, lost engine power and nosed over during a forced landing near San Jose, California. The private pilot, who was the sole occupant, was not injured; the airplane sustained substantial damage. The pilot/owner operated the airplane under the provisions of 14 CFR Part 91 as a personal flight. Visual meteorological conditions prevailed and a flight plan was not filed. The local flight departed Reid-Hill View Airport (RHV), San Jose, California, at 1215. According to the pilot, he was flying above hilly terrain southeast of the airport when he heard a loud bang, followed by a violent vibration coming from the engine. The pilot added that the engine did not experience a total loss of power, but performed poorly due to the severe vibration. The pilot reduced the throttle and the vibration subsided, but when he added more throttle the violent vibration returned. The pilot then decided that it was unsafe to continue the flight and began searching for a place to land. He made a forced landing in a pasture, which was uneventful until one of the main landing gear contacted a "deviation" in the ground. The airplane nosed over and came to rest inverted. In a phone interview with the investigator-in-charge, a mechanic, who recovered the wreckage, reported that he examined the engine and discovered that the number 3 cylinder exhaust valve was stuck. The corresponding push rod tube was also bent, and the number 3 connecting rod was still intact.