On July 12, 1998, approximately 1726 Pacific daylight time, a Beech 23, N8719M, registered to and being flown by a private pilot, was substantially damaged during an off airport forced landing following an abrupt loss of engine power three nautical miles northwest of Oakville, Washington. The pilot and his two passengers were uninjured. Visual meteorological conditions prevailed and a VFR flight plan had been filed. The flight, which was personal, and destined for Elma, Washington, was to have been operated under 14CFR91, and originated from Aurora, Oregon, approximately 1620 The pilot reported that while about ten miles southeast of Elma, the engine started vibrating violently and losing power without warning. He had no success at restoring power using emergency procedures. He stated that he declared an emergency and, unable to maintain altitude, he executed a forced landing in a soft open field of 12 inch high corn. During the roll-out, the nose landing gear separated and the left main landing gear collapsed. The engine was inspected at a maintenance facility at Olympia, Washington. During teardown of the engine, it was determined that the exhaust valve on the number 3 cylinder had failed, with the valve head broken off just below the tulip. This valve was of the hollow sodium-filled type. The aircraft's engine logbook (kept with the airplane) contained a note dated September 11, 1995, at a tachometer reading of 1790 hours, and reporting that the previous log books had been lost. An annual inspection was performed that date, and there was a note that the O-320-D2B engine, serial number L-5772-39, was 790 hours past its major overhaul. A later log entry (May 7, 1996) indicated that this time since overhaul had been corrected from 790 hours to 867 hours at a tachometer reading of 1817. This log entry indicated that the engine was overhauled on December 2, 1966, by Flightcraft, Portland, Oregon. The stem of the failed exhaust valve was dimensionally checked at .433 inches in diameter, or a nominal dimension for 7/16 inch valves (measured at the valve stem). The Airworthiness Directives (AD) listing in the reconstructed log books for the engine noted that AD 63-23-02 "Exhaust valves and guides DNA (does not apply) by SN (serial number)." AD 63-23-02 requires recurrent inspection and replacement of valves and/or valve guides at intervals of a maximum of 500 hours, depending upon the operational environment of the airplane, and depending upon the part number of the camshaft in the engine. That AD refers to Lycoming SB (service bulletin) 293B, which lists, in part, that the applicability of this AD included -D series engines with serial numbers of 5086-39 and up. No record of compliance with this AD note prior to the reconstruction of the log books was found, and no record was found as to which camshaft was installed at the reported overhaul.