On April 9, 2003, at 1635 central daylight time, a Piper PA-22-108, N4860Z, piloted by a private pilot, sustained substantial damage during a forced landing near Rose Hill, Kansas. Visual meteorological conditions prevailed at the time of the accident. The personal flight was operating under the provisions of 14 CFR Part 91 without a flight plan. The pilot was not injured and his passenger reported minor injuries. The flight departed Eureka Municipal Airport (13K), Eureka, Kansas, at 1550 and was en route to Cook Airfield (K50), Derby, Kansas, at the time of the forced landing. According to the pilot's written statement, about one mile east of Rose Hill the engine began "cutting out." The pilot reported the engine "would run for 2 or 3 seconds and cut out for 2 or 3 seconds, over and over again." The pilot stated he applied carburetor heat and selected a different fuel tank, with no effect on engine performance. The pilot reported he performed a forced landing to a hayfield and during the landing rollout the airplane nosed over after encountering a soft area of the field. An inspector with the Federal Aviation Administration performed the on-scene investigation. The carburetor was reinstalled on the engine, as it had become detached during the accident. An engine test run was performed and at first the engine would not start. The spark plugs were removed and cleaned due to oil fouling. The spark plugs were reinstalled and the engine started. A magneto check was performed and the engine would not operate on the left magneto. The left magneto was disassembled and the timing gear keeper was found laying loose in the case. The keeper, timing gear keyway slot, and magneto drive shaft were all worn. The timing gear and keeper were replaced with serviceable components and the magneto was reinstalled on the engine. The engine operated on both magnetos, with acceptable engine rpm drops when selected on the individual magnetos. The magneto manufacturer issued a service bulletin during June 1972 that called for the replacement of cam washers (p/n 10-51354) having a thickness of 0.063-inches with a thicker 0.095-inches washer. The purpose of the replacement was to "insure secureness of the magneto cam to magnet shaft." The magneto's cam washer from the accident aircraft was measured with a dial-caliper and was 0.063-inches thick.