On May 11, 2007, about 1615 Pacific daylight time a Piper PA-24, N8170P, experienced the collapse of its landing gear during rollout on runway 34 at Eugene, Oregon. As the airplane slid to a stop, bulkheads were bent and the firewall was deformed. The airplane was substantially damaged. Neither the commercial pilot nor the three passengers were injured during the personal flight in the airplane, which the pilot owned and operated. Visual meteorological conditions prevailed at the time, and no flight plan had been filed. The flight was performed under the provisions of 14 Code of Federal Regulations Part 91, and it originated from Santa Rosa, California, about 1345. According to the pilot, approaching the destination airport he attempted to extend the landing gear. When he moved the landing gear control to the down position, the gear did not extend. In an attempt to rectify the situation the pilot cycled the gear handle again, but the gear did not extend. The pilot further reported that he observed the airplane's generator was producing current. The pilot pulled and reset the landing gear circuit breaker, and again attempted to extend the gear. This time, the gear extended and the single green gear down light illuminated. The pilot opined that the gear was down and locked, and he proceeded to land. The touchdown was uneventful. However, after a couple of seconds the gear collapsed. The airplane's landing gear extension system was subsequently examined under the direction of the National Transportation Safety Board investigator. According to the Chief Inspector, Flightcraft, Eugene, due to impact damage of the landing gear actuator aft mount, the landing gear could not be operated with electric power. The airplane's master switch was turned on, and no panel anomalies were observed. Each landing gear was then manually retracted and extended three times. Each time, when extended, the gear locked down over center, and a green down and locked light indication occurred. The gear motor was electrically activated, and the motor sounded normal. The reason for the gear's failure to fully extend to the locked down position was not ascertained.