What was found
DURING FLIGHT, OIL PRESS WAS INDICATING LOW (10-30 PSI) AND ERRATIC. AFTER LANDING, DURING TAXI, OIL PRESS INDICATION WAS 0-10 PSI. PRESS XMITTER REMOVED AND A DIRECT READING GAUGE CONFIRMED THAT ON-BOARD INDICATIONS WERE CORRECT. PRESS REGULATOR AND BYPASS VALVES WERE CHECKED, FOUND NORMAL AND UNOBSTRUCTED. ENG IS EQUIPPED WITH A CHRISTEN 802 INVERTED OIL VALVE INSTALLED AT THE SUPPLY SIDE OF THE OIL PUMP. UPON REMOVAL AND DISASSEMBLY OF SAME, THE UPPER OF THE TWO CHROME BALLS (1.1250 INCH DIAMETER) WAS FOUND CORRODED CAUSING OIL PUMP TO SUCK AIR WHILE IN THE UPRIGHT ATTITUDE AND ENABLING CAVITATION. THE LOWER BALL, UNLIKE THE UPPER, IS CONTINUOUSLY BATHED IN OIL AND WAS FOUND IN LIKE-NEW CONDITION.