On October 12, 1997, at 1500 hours Pacific daylight time, a Cessna 170A, N9212A, ground looped while attempting to land at the Gansner Field Airport, Quincy, California. The aircraft sustained substantial damage and the commercial pilot and three passengers were not injured. The aircraft was owned and operated by the pilot, and was completing a personal cross-country flight from Chico, California. Visual meteorological conditions prevailed and included light and variable wind conditions. In his written statement, the pilot reported that the approach, landing flare, and touchdown were normal. He further stated that during the initial ground roll, a very strong tailwheel vibration began and "shook the plane and overrode my rudder controls." The pilot was unable to regain control and the aircraft veered to the left, then ground looped in a very tight circle. Written statements submitted by the passengers were consistent with the pilot's report. An Federal Aviation Administration airworthiness inspector from the Reno, Nevada, Flight Standards District Office examined the runway and the aircraft. He reported that tail wheel scrub marks were present on the runway pavement in a high frequency wave pattern which led to the point of the ground loop. Examination of the aircraft disclosed about 1/8-inch play in the tail wheel bearings. The inspector also reported that the tail wheel was improperly shimmed. Review of the maintenance records disclosed that the tail wheel was replaced 12 days prior to the accident. The work orders from the repair shop which installed the unit noted that the tail wheel assembly was supplied by the owner. The work order notes that the bearings were replaced by the shop at the time of installation.