On March 20, 2001, at 1500 hours Pacific standard time, a Cessna 172RG, N6307R, lost engine power and made an emergency landing in an open dirt field in Stanford, California, where it came to rest inverted. The airplane was operated by the West Valley Flying Club as an instructional flight under the provisions of 14 CFR Part 91, and sustained substantial damage. The certified flight instructor (CFI) and the private student pilot were not injured. Visual meteorological conditions prevailed for the local area flight. The flight departed from the Palo Alto Airport of Santa Clara County, Palo Alto, California, at 1416. No flight plan had been filed. The flight was scheduled to terminate at the Palo Alto airport. The purpose of the flight was to provide instruction for a complex airplane checkout. The CFI stated that they were over Webb Ranch, about 2,000 feet msl, when he noted a loss of oil pressure. He contacted the Palo Alto Air Traffic Control Tower and declared an emergency. He stated the engine stopped at 1,600 feet. He and the student pilot shutdown the airplane systems. He noted at one point the cockpit filled with smoke and they had to open the windows. The CFI set up for the emergency landing on a side road. A truck entered the road, and he had to maneuver the airplane onto an adjacent open field. On the landing rollout the nose landing gear dug into the soft dirt and the airplane nosed over. The student pilot stated that they were getting ready to go back to home base when the CFI asked him if he heard knocking. He replied that he heard the knocking. They both observed the oil pressure was at zero. The knocking continued to increase in intensity. The CFI declared an emergency and landed in an open field. A Federal Aviation Administration (FAA) inspector inspected the engine. A Textron Lycoming engine manufacturer's representative, who was a party to the investigation, assisted the FAA. They found that the oil filter had not been tightened or safety wired to the engine. The bottom of the fuselage, firewall, and the rear of the engine were coated with oil. The engine was seized. A Safety Board investigator conducted a review of the airframe and engine logbooks. It was noted that the last annual inspection was completed on March 21, 2000. On March 19, 2001, maintenance was performed on the airplane that included an oil change.