A B737-500 TECHNICIAN WHILE WORKING TO GAIN CLRNC FOR AN AILERON CABLE; A FUEL XFEED VALVE WAS DISCONNECTED AND MOVED CUTTING THE SEAL CAUSING A FUEL LEAK.

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ON NOV/FRI/02; I WAS WORKING ON WRITE-UP X IN CONJUNCTION WITH WRITE-UP Y. THE DISCREPANCIES IN QUESTION WERE MARKED IN RED OR THE COMPONENTS TROUBLE SPOTS. I LOOSENED THE UPPER AND LOWER AFT BOLTS ON THE EDP SUPPLY SHUTOFF VALVE; REPOSITIONED THE VALVE AND RETORQUED THE BOLTS R AND F MM 29-15-94; MAINT MANUAL 20-50-11-0201 AND SRM 51-40-04. THIS PROVIDED VERY LITTLE CLRNC BTWN THE AILERON CABLES AND THE VALVE X; BUT INSUFFICIENT CLRNC BTWN THE SHUTOFF VALVE AND THE FUEL XFEED VALVE. I THEN PROCEEDED TO LOOSEN THE NUTS ON THE FUEL XFEED VALVE A LITTLE AT A TIME; ASSUMING THE VALVE MIGHT BE ABLE TO SHIFT ENOUGH TO PROVIDE CLRNC AT THE CONTACTING POINTS. ABOUT XA40 PM THE VALVE STARTED TO LEAK FUEL. I QUICKLY TOLD THE MECH ON THE HEADSET TO INFORM THE COCKPIT PERSON THAT WE HAD A FUEL LEAK AND PWR WAS CUT. I NOTICED WHERE THE FUEL WAS LEAKING; THE O-RING THAT HAD BECOME UNSEATED ON THE XFEED VALVE. I QUICKLY TIGHTENED THE NUTS ON THE VALVE AND THE LEAK WAS TEMPORARILY STOPPED. ALTHOUGH WE WERE ABLE TO FINISH OUR MAINT CHKS; THIS ERROR HAD CREATED AN INSPECTION WRITE-UP TO REPLACE THE O-RING IN THE XFEED VALVE. THE FOLLOWING 2 SHIFTS HAD TRANSFERRED FUEL AND REPLACED THE XFEED VALVE AND O-RING. A FUNCTIONAL TEST WAS PERFORMED; NO LEAKS WERE FOUND AND THE ACFT WENT ON A POST HMV TEST FLT THAT EVENING. ALL APPEARED TO FUNCTION NORMALLY.