ENG GEAR BOX SEAL REPLACED WITH ROUTINE POST MAINT CHKS. SEAL FAILED INFLT.

Narrative

ACFT OF B-747 FLEET HAD AN IDG REMOVED FROM #4 ENG DURING ROUTINE MAINT. WHILE THE IDG WAS REMOVED THE SEAL BTWN THE IDG AND THE GEAR BOX WAS REPLACED BECAUSE OF WEAR. AFTER THE IDG WAS REINSTALLED AND THE ENG HAD BEEN CLOSED AN OIL LEAK WAS DETECTED UNDER #4 ENG. THE ENG WAS DRY MOTORED IN THE HANGAR AND SAID TO BE OK FOR SVC. ANY TIME A COMPONENT SUCH AS AN IDG IS REMOVED OR REPLACED; AN ENG RUN IS REQUIRED AFTER IT LEAVES THE HANGAR AND BEFORE BEING RETURNED TO SVC. AN ENG RUN WAS COMPLETED AND NO MAJOR OIL LEAK WAS DETECTED. AFTER THE ACFT WAS RETURNED TO SVC AND LEFT SFO; #4 ENG HAD TO BE SHUT DOWN INFLT AND THE ACFT HAD TO RETURN TO SFO. WHEN COMPONENTS SUCH AS AN IDG ARE REMOVED OR REPLACED; THESE COMPONENTS SHOULD BE MADE TO PERFORM LIKE THEY WOULD PERFORM INFLT; BEFORE THEY ARE RETURNED TO SVC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR MECH SAYS THAT AFTER THE SEAL WAS REPLACED BTWN THE IDG AND THE GEAR BOX; THE ENG WAS DRY MOTORED AND CHKED OK. THEN; BEFORE RETURNING TO FLT; A 5 MIN IDLE CHK WAS MADE; STILL WITHOUT ANY LEAK. HOWEVER; THE RPTR THINKS THAT A HIGH PWR ENG RUN SHOULD BE MADE IN ORDER TO PUT A GREATER LOAD ON THE ENG. BECAUSE; IN THIS INCIDENT WHEN INFLT THE SEAL MALFUNCTIONED AND THE ENG HAD TO BE SHUTDOWN.