On July 5, 1993, about 1630 hours eastern daylight time, N61058, a Cessna 150 with a tail wheel conversion, was substantially damaged after ground looping on landing at the Pittsfield Airport, Maine. The airplane was operated by John M. Miller, Carmel, Maine. The pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and a flight plan was not filed. The personal flight originated from Newport, Maine, about 1600 hours, and was conducted under 14 CFR 91. The pilot reported that the accident occurred about one hour of flight time since the airplane's last annual inspection. Prior to the inspection, the pilot stated that the airplane had tailwheel control problems and "tailwheel shimmy"; he had asked that these problems be checked and repaired. Following the annual inspection, the pilot departed from his private airstrip in Newburgh, Maine, and performed a landing onto another grass strip at the Newport Skypark, Maine. He then departed from the Newport Skypark and flew to the Pittsfield Airport. This airport has a 4,000 foot paved runway. He reported that after a "normal" approach with no wind, the airplane had a "severe tailwheel vibration and shimmy" after touchdown. The pilot stated that the airplane then veered sharply to the right and he "had no control using the tailwheel." The airplane ground looped and the left main landing gear collapsed. According to an FAA Aviation Safety Inspector, post impact damage to the tailwheel assembly prevented a reliable determination of the existence of any pre existing mechanical malfunctions.