On July 1, 2001, at 0705 Pacific daylight time a Cessna 172N single engine airplane, N737SH, nosed over during a forced landing near Boulder City, Nevada. The forced landing was precipitated by a loss of engine power during cruise flight. The private pilot and three passengers were not injured, and the airplane sustained substantial damage. The airplane was registered to a private individual and was operated by Westair Aviation, North Las Vegas, Nevada, under the provisions of 14 CFR Part 91. The personal flight departed Boulder City at 0655, and was destined for North Las Vegas. Visual meteorological conditions prevailed, and a flight plan was not filed. According to a Federal Aviation Administration (FAA) inspector who responded to the accident site, during the pilot's preflight he had visually estimated 15 gallons of fuel in each tank prior to departure from North Las Vegas earlier that day. A substantial amount of fuel was observed at the accident site. The inspector also stated that the airplane had made a forced landing due to a loss of engine power at Jean, Nevada, on June 29, 2001. The airplane sustained structural damage to it wings and empennage. The Lycoming O-320-H2AD engine (serial number L-5102-76T) had accumulated 302.2 total hours since its last overhaul. The airplane was relocated to the facilities of Air Transport, Phoenix, Arizona, where on July 24, 2001, an FAA inspector, along with an investigator from Textron Lycoming, examined the engine. The engine remained attached to the airframe at the engine mount, and appeared relatively undamaged. The top spark plugs were removed, examined, and compared to the Champion Check-A-Plug A-27 chart. The spark plug electrodes were mechanically undamaged and exhibited coloration consistent with normal operation. Thumb compression was confirmed in the proper firing order when the propeller was rotated manually. The dual magneto was found secured to its mounting pad with the distributor cap and wires in place. Both "P" leads were secure in their respective ports. A magneto synchronizer was attached at the magneto "P" leads to check the magneto to engine timing. The magneto timing check indicated the left and right points were not opening. The magneto distributor cap was removed to provide a visual examination of the contact assemblies. During manual rotation of the propeller, the points were examined and found not to be opening as the magneto cam rotated. The magneto (part number D4RN-3000, serial number 1268803G) was removed from the engine and was taken to Homes Aviation, Chandler, Arizona, for further examination. It was confirmed that the points would not open during cam rotation. It was also placed on a test bench and no sparks were noted through the ignition harness. The facility then reset the contacts and timing and retested the magneto. The magneto was found operationally functional after the contact and timing work. A review of the maintenance records revealed the engine underwent its last 100-hour inspection on June 28, 2001, at an airplane total time of 7,270.5 hours, and 299.1 hours since the engine overhaul The inspection occurred 3 operating hours prior to the accident. On June 30, 2001, a maintenance entry indicates the magneto internal timing was reset in accordance with the manufacturer's maintenance manual. The airplane and engine total time was not indicated with this maintenance action. At the time of the accident, the airplane had accumulated a total time of 7,273.6 hours.