What was found
ENGINE WAS AT CRUISE POWER. LOUD BANG. SMALLER BANGS. ENGINE RAN, BUT DID NOT PRODUCE APPRECIABLE POWER. FORCED LANDING IN TUNDRA NEAR NOATAK, ALASKA FOLLOWED. NO DAMAGE. FOUND SUPPORT LUGS FOR EXHAUST VALVE ROCKER ARM FAILED ON NR 6 CYLINDER. INTAKE MANIFOLD WAS SEPARATED AT RUBBER COUPLING ON RT FWD SIDE OF ENGINE AND CROSS TUBE WAS BENT FORWARD AGAINST COWLING ALLOWING ENGINE TO INTAKE OUTSIDE AIR.