What was found
ENROUTE, IFR AT 17000 FT WHEN PILOT NOTICED DROP IN MANIFOLD PRESSURE. PILOT REDUCED POWER SETTINGS AND STARTED DESCENT . NEXT OIL PRESSURE AND MANIFOLD PRESSURE DROPPED SIGNIFICANTLY AND DECLARED AN EMERGENCY, FEATHERED THE PROP AND SHUTDOWN THE ENGINE. MADE AN EMERGENCY LANDING WITH DAMAGE TO GEAR AND PROPELLERS. ENGINE WAS EXAMINED, THE PROPELLER ROTATED WITH PROPER RESISTANCE AND CONTINUITY TO THE ACCESSORY SECTION WAS ESTABLISHED. CRANKSHAFT APPEARED TO BE OPERATIONAL. ALL VALVES AND PISTONS OPERATED NORMALLY. THE ENGINE HAS A CAPACITY OF TEN QUARTS. NO DAMAGE COULD BE FOUND INSIDE OF ENGINE. THERE WAS NO OIL RESIDUE IN EXHAUST STACK OR LEAKING FROM ENGINE. THE AIR-OIL SEPARATOR HAD EXTENSIVE AMOUNT OF OIL FLOWING FORM VENT TUBE. IT APPEARS THAT A PISTON RING FAILURE OR A BURNED HOLE IN A PISTON CAUSED EXCESSIVE PRESSURE IN THE ENGINE BLOCK CAUSING THE OIL TO BE BLOWN OUT THE AIL/OIL SEPARATOR.