On October 27, 1999, approximately 1135 mountain daylight time, a Bellanca 8KCAB, N8707V, registered to and operated by Kempton Air Service, was substantially damaged when it collided with terrain during landing roll at Walker Field, Grand Junction, Colorado. The commercial certificated flight instructor and one passenger were not injured. Visual meteorological conditions prevailed, and a VFR flight plan had been filed for the personal flight being conducted under Title 14 CFR Part 91. The flight originated at 1100. According to the pilot, after flying for one half of an hour in the local area, he returned to the airport to practice landings. He made a "normal" tailwheel landing on runway 11 and landed 1,000 feet down the runway. He stated that at the time he landed, the wind was light from 110 degrees. During rollout approximately 200 feet down the runway, the left main landing gear collapsed and separated from the aircraft. The airplane ground looped and departed the runway to the left, turning 180 degrees and coming to rest on its left side. The propeller was damaged, and the left wing strut and left rear wing spar were bent. Postaccident examination of the airplane revealed that the left main landing gear u-bolt failed. The u-bolt was sent to the NTSB's Materials Laboratory for examination. According to their report, the bolt fractured through the bend between the horizontal and vertical leg of the bolt. The fractured surface revealed ratchet marks and crack arrest positions typical of fatigue cracking. The fatigue initiated at several origins on the inner radius of the bend and disseminated through approximately 80 percent of the bolt cross section. The fractured features on the remaining fractured surface were typical of an overstress failure. The intact vertical leg was bent outward, creating an approximate 120-degree angle with the horizontal leg. No evidence of cracking was observed on the inner radius surface of the bend between the vertical and horizontal leg. The inner surface of the bolt on each side of the bend between the separated vertical leg and the horizontal leg was rubbed. According to their report, the fractured surface of the bolt at the failure initiation area was damaged following the separation and the reason for the fatigue initiation was unable to be determined.