HISTORY OF FLIGHT: On September 10, 1994, at 1326 central daylight time, a Cessna 175, N7554M, was substantially damaged during a forced landing near Oklahoma City, Oklahoma. The private pilot and the pilot rated passenger received fatal injuries. Visual meteorological conditions prevailed for the local personal flight. During interviews and on the enclosed statements, witnesses reported the information in this paragraph. The airplane departed runway 16 at Downtown Airpark, Oklahoma City, Oklahoma. During the initial climb at approximately 25 feet above the runway, engine sounds ceased and the propeller "was stationary in a vertical position." The airplane touched down with flaps extended and during the landing roll, on the grass area beyond the departure end of the runway. The airplane traversed "rough and uneven terrain" and struck a dirt bank and became airborne. The aircraft was observed to descend into a 25 foot deep ravine. PERSONNEL INFORMATION: Federal Aviation Administration records revealed that the passenger was also a rated private pilot who obtained a third class medical certificate on December 27, 1979, and his private pilot certificate on May 8, 1980. Since 1980 there is no record of any pilot activity, either flight or medical issuance. AIRCRAFT INFORMATION: The airplane was registered to the private pilot on May 13, 1988. Aircraft records were never made available to the investigator- in-charge. WRECKAGE AND IMPACT INFORMATION: The airplane came to rest on a measured magnetic heading of 150 degrees at the base of a 25 foot ravine. Ground scars were found in the grass area beyond the departure end of the runway. See the enclosed diagram for additional details. The baggage compartment and empennage were buckled downward and the airframe and engine were intact. The fuel selector was found in the "OFF" position; however, fire department personnel reported turning the "fuel shut-off" as fuel was leaking from the airplane. An examination of the flap actuator revealed the retracted position and flight control continuity was confirmed. One propeller blade was bent aft and the crankshaft did not rotate a complete revolution. The throttle control in the cockpit was found in the idle position with the linkage at the engine indicating midrange. Fuel was found in the fuel lines to the gascolator and the gascolator screen contained debris. The gascolator fuel screen and the engine were forwarded to Mobile, Alabama, for examination. MEDICAL AND PATHOLOGICAL INFORMATION: An autopsy and toxicology testing were not performed. TEST AND RESEARCH: On october 14, 1994, the engine, accessories, and fuel gascolator were examined (report enclosed) at Teledyne Continental Motors in Mobile, Alabama. Metallic debris was found in the engine oil sump and in the residual oil. The pump cavity exhibited scratches in the cavity walls. The oil pressure line was not identified as a Teledyne Continental Motors (TCM) line. Fuel was found in the carburetor and during flow testing, fuel passed through the fuel gascolator. Engine binding was noted during rotation. The front reduction gear case was removed from the engine. The propeller shaft thrust bearings fit loosely on the journal; they exhibited rotational scratches. A review of the engineering drawings and published parts lists established that these bearings were not the correct part for this installation. Both the propeller drive gear bearings were solid in lieu of the required split type. The propeller drive gear front bearing was seized to the propeller drive gear. Physical evidence on the bearing indicated that it had been modified to fit the installation. Further examination of the bearing failed to identify the source of manufacture, there were no identification markings. The metallurgist further identified that the bearing material was brass. The engineering drawings require a steel bearing with locking tab for this installation. The crankcase and the forward gear case exhibited galling and metal debris identified as aluminum from the forward gear case. The engine had scratches in the main bearings and rod bearings. ADDITIONAL INFORMATION: The airplane was released to the owner's representative.