On May 31, 1993, at 1315 Alaska daylight time, a retractable wheel equipped Cessna 310 airplane, N5847M, registered to and operated by the Pilot-in-Command, experienced a collapse of the nose gear upon landing at the Kodiak Airport, Kodiak, Alaska. The personal flight, operating under 14 CFR Part 91, departed Kodiak for a local maintenance test flight. Visual meteorological conditions prevailed and no flight plan was filed. The Airline Transport Pilot-in-Command and the mechanic/passenger were not injured and the airplane received only minor damage. According to the Pilot-in-Command, the nose gear made a loud noise upon retraction and then would not lock down during the subsequent extension. Examination of the system showed a failure of the nose gear idler bell crank. Metallurgical examination of the idler bell crank by use of the bench binocular microscope showed that the fractures revealed features typical of over stress separations. According to the Pilot-in-Command/owner and the mechanic, after the mishap, they simply replaced the idler bell crank and performed a gear extension and retraction check while the airplane was on jacks. The gear performed perfectly and they were not able to duplicate the problem. The nose wheel centering mechanism was examined and no anomalies were noted. According to the mechanic, the landing gear was rigged properly.