What was found
DURING CLIMB OUT, THE PILOT NOTICED THE RIGHT ENGINE OIL PRESSURE GAGE INDICATING A SIGNIFICANT INCREASE IN PRESSURE. WHEN THE RIGHT ENGINE STARTED TO RUN ROUGH THE ENGINE WAS SECURED AND THE PROPELLER WAS FEATHERED AS A PRECAUTION. THE AIRCRAFT RETURNED TO THE AIRPORT OF DEPARTURE AND LANDED WITHOUT FURTHER PROBLEMS. AFTER THE RIGHT COWLING WAS REMOVED TO INVESTIGATE THE ROUGH RUNNING ENGINE, IT WAS FOUND THAT THE ENGINE HAD BLOWN THE NUMBER 4 CYLINDER OFF OF THE CRANKCASE, ALLOWING THE PISTON TO COCK IN THE CYLINDER BARREL AND THROWING THE NUMBER 4 ROD, DAMAGING THE CRANKCASE. THE ENGINE CANNOT BE ROTATED BY HAND.