A B747-400 CREW; TAXIING FOR TKOF AT SFO; STRAYED FROM TXWY CTRLINE COMING INTO CONTACT WITH A TXWY SIGN.

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WHILE ON TXWY A; ABEAM OUR GATE; TXWY A WAS BLOCKED BY ACFT Y WAITING FOR GATE. CAPT ELECTED TO TAKE TXWY B2 TO TXWY B TO TXWY B1 TO TXWY A. GND CTL CLRED US. AS WE MANEUVERED; WE APPEARED TO BE R OF CTRLINE; BUT WELL WITHIN LIMITS OF TXWY. WE LATER BECAME AWARE THAT THE #4 ENG HAD COME IN CONTACT WITH A TXWY SIGN. AT NO TIME THROUGHOUT THE MANEUVER DID ANY OF THE CREW FEEL A CONCERN FOR ENG CLRNC. THE ONLY AREA OF CONCERN WAS REGARDING BEING SLIGHTLY R OF CTRLINE DURING RATHER TIGHT MANEUVERING. I WAS AWARE THAT THE WING WAS OVERHANGING THE ISLAND AREA; BUT I THOUGHT THAT WE SHOULD HAVE PLENTY OF CLRNC VERTLY. SUPPLEMENTAL INFO FROM ACN 548589: I WAS AWARE THAT I WAS MAKING USE OF THE ENTIRE WIDTH OF THE TXWYS TO MAKE THE INITIAL L TURN FOLLOWED BY THE 90 DEG TURN ONTO TXWY B; THEN TO TXWY B1; WHERE WE RE-ENTERED TXWY A. MY MAIN EFFORT WAS TO ENSURE THE ACFT STAYED ON THE TXWY. A FEW MINS LATER AT TXWY ECHO; ON TXWY A; WE WERE TOLD TO RETURN TO GATE FOR WT AND BAL PROB. AT GATE; WE WERE ADVISED BY MECH THAT THERE WERE SCRAPES ON BOTTOM OF ENG #4 FROM CONTACT WITH TXWY SIGN. AT NO TIME WERE ANY OF US AWARE OF THIS. I HAVE MADE THE SAME TURNS ON TAXI OUT 2 TIMES BEFORE WITH NO PROBS; BUT DID NOTE NOT MUCH ROOM. OTHER 2 TIMES I WAS ABLE TO OFFSET RIGHT BEFORE TURN. THIS TIME COULD NOT SINCE WE WERE AT TXWY B2 ALREADY. CALLBACK CONVERSATION WITH RPTR ACN 548590 REVEALED THE FOLLOWING INFO: AN ARPT OPS SPECIALIST REVEALED THAT STRICT ADHERENCE TO TXWY CTRLINES IS REQUIRED; ESPECIALLY IN THE AREA REFERRED TO IN THIS RPT; IF OBSTACLE CLRNC IS TO BE ASSURED.