On September 2, 1996, at 0746 mountain daylight time, a Piper PA-32R-300, N7640F, was substantially damaged during a forced landing at Salida, Colorado. The commercial pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under Title 14 CFR Part 91. The flight originated at Pueblo, Colorado, on September 2, approximately 0700. According to the pilot, he was in level cruise flight at 12,500 feet, 8 miles south of Salida, Colorado, en route to Gunnison, Colorado, when, without warning, the engine lost power. The pilot said he switched fuel tanks and turned on the boost pump, but the engine did not respond and the propeller continued to windmill. The pilot was able to glide the airplane to the Salida Airport, but landed short. He lowered the landing gear and deployed flaps. The right wing struck a fence post, causing the airplane to skew 90 degrees. The landing gear collapsed and the airplane skidded to a halt. On September 26 and 27, 1996, the engine was examined at Jensen Aircraft in Salida under the direction of an FAA airworthiness inspector. After the air filter had been removed, the alternate air valve discs and a broken bolt was found laying in the induction system. The valve mounting arm was found loose on the actuating shaft with approximately 45 degrees of play. The scat tubing from the alternate air box to the injector box was found to be deteriorated. The No. 6 spark plug had been damaged by fod (foreign object debris), and the lower No. 2 spark plug was filled with oil. The No. 6 cylinder was boroscoped. The cylinder appeared to be in good condition, but the piston had sustained impact damage from the remains of the other half of the retaining bolt. It was the opinion of both Jensen Aircraft and the FAA airworthiness inspector that failure of the alternate air box bolt caused the valve to shut, blocking the induction system and starving the engine of air. The other half of the failed bolt was ingested into the No. 6 cylinder through the intake valve.