What was found
PILOT EXPERIENCED AN ROUGH RUNNING LT ENGINE 20 MINUTES INTO THE FLIGHT. THE PILOT REPORTED THAT ALL LT ENGINE INSTRUMENT INDICATIONS WERE NORMAL AT THAT TIME. OIL PRESSURE DROPPED TO ZERO, TURNED BACK TO AIRPORT. DECLARED AN EMERGENCY AND LANDED WITHOUT ANY FURTHER INCIDENT. AFTER INSPECTION OF THE LT ENGINE, A HOLE WAS FOUND IN THE TOP OF THE ENGINE CASE BETWEEN CYLINDERS 5 AND 6. AT THE TIME OF THIS REPORT, THE LT ENGINE HAD NOT BEEN TORN DOWN TO INVESTIGATE THE CAUSE FURTHER. IT APPEARS THAT A POSSIBLE CONNECTING ROD AND BEARING WOULD BE THE CAUSE OF THE FAILURE.