As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE DEVELOPED ROUGHNESS, DETERMINED TO BE MAGNETO FAILURE. PILOT LANDED AND TAXIED ON BEACH WHERE IT WAS DETERMINED THE EXHAUST ROCKER CHAMBER NR 1 CYLINDER HAD CRACKED, PRESUMABLY FROM ENGINE ROUGHNESS. BOTH COMPONENTS WERE REPLACED.