On June 12, 1996, about 1415 eastern daylight time, a Brantly B-2 helicopter was substantially damaged at Oswego County Airport, Fulton, New York. The certificated flight instructor(CFI) and private pilot were not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the local flight conducted under 14 CFR Part 91. According to the NTSB Form 6120.1/2, the CFI stated that he noticed loose nuts on the intake manifold during pre-flight. The CFI and student pilot tightened the nuts and continued with the instructional flight. After takeoff and 40 to 45 minutes of maneuvers, they landed the aircraft, turned off power, and exited. They said that they wanted to check the intake manifold. After finding all satisfactory, they performed a maintenance run to check the manifold pressure. After raising the manifold pressure up to 26 inches the pilot said the aircraft became "light on the skids" but did not break ground. After setting the aircraft back down it rolled left and to the rear. The main rotor blades impacted the ground and separated from the aircraft. Post accident examination of the wreckage by the FAA Inspector revealed the left rear oleo strut had failed by separating from the top of the strut. Also, sets of skid marks were found leading to the accident location. The first set were found approximately 50 feet away.