As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AKN - EN ROUTE AIRCRAFT EXPERIENCED ENGINE ROUGHNESS. PILOT LANDED AIRCRAFT AT REINDEER BAY, NAKNEK LAKE. PROBLEM WAS DETERMINED TO BE EXHAUST SIDE ROCKER CHAMBER CRACKED THROUGH ROCKER AXLE PIN BORES. SUSPECT CAUSES: COULD BE INCORRECT ROCKER AXLE TORQUE OR VALVE STICKING.