MECHANIC REPORTS A B757-200 RETURNED TO FIELD AFTER REPLACING NOSE GEAR DOOR ACTUATOR FROM COMPANY INVENTORY. THE AMM PROCEDURE DOES NOT CALL OUT FOR A GEAR SWING WHEN CHANGING DOOR ACTUATOR.

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REMOVED AND REPLACED NOSE GEAR DOOR ACTUATOR IN ACCORDANCE WITH AMM. OPS CHKED GOOD ON THE GND. ACFT DEPARTED AND RETURNED TO THE FIELD AFTER TKOF WITH NOSE GEAR INDICATION PROB. A BAD PART FROM THE VENDOR. THE ACTUATOR WAS LAID SIDE-BY-SIDE WITH THE OLD ACTUATOR WITH BOTH FULLY EXTENDED AND THE NEW ACTUATOR FROM THE VENDOR WAS APPROX 1 INCH SHORTER. WE BORROWED AN ACTUATOR FROM ACR X AND WAS INSTALLED ON OUR ACFT. THE ACTUATOR WAS THEN INSTALLED INTO THE ACFT. THE NOSE LNDG GEAR WAS OPS CHKED PER THE AMM WITH NO FAULT NOTED. THE ACTUATOR FROM THE VENDOR WOULD NOT FULLY EXTEND. THIS WOULD NOT LET THE HYD FLUID FLOW THROUGH THE SEQUENCE VALVE; THUS NOT LETTING THE NOSE GEAR TO RETRACT. I DON'T KNOW HOW TO AVOID THIS FROM HAPPENING AGAIN. THE JOB WAS ACCOMPLISHED STEP-BY-STEP FROM THE AMM AND THIS EVENT STILL HAPPENED. MAYBE THE VENDORS THAT OUR COMPANY USES NEED TO HAVE BETTER QUALITY CTL ON THE PARTS THAT THEY OVERHAUL. THE AMM FOR THE JOB COULD ALSO CALL OUT FOR A NOSE GEAR SWING FOR THE REPLACEMENT ON THE NOSE LNDG GEAR DOOR ACTUATOR REPLACEMENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE NOSE GEAR DOOR ACTUATOR HE INSTALLED BEFORE THE B757-200 DID A RETURN TO FIELD; CAME FROM HIS COMPANY STORES. THE AMM ONLY REQUIRES MAINT TO RECYCLE THE NOSE GEAR DOOR HANDLES AND VERIFY THE DOORS OPEN AND CLOSE AND ARE FAIRED TO THE ACFT FUSELAGE. WHEN THE ACFT RETURNED; THEY JACKED THE NOSE GEAR TO PERFORM A GEAR SWING. THE NOSE GEAR WOULD BREAK OVER AND UNLOCK BUT WOULD NOT COME UP; BECAUSE THE GEAR DOORS DID NOT OPEN AS WIDE AS THEY SHOULD HAVE. THE LACK OF PROPER DOOR OPENING; PREVENTED THE SEQUENCE VALVE FROM PORTING FLUID TO THE LANDING GEAR ACTUATOR TO RETRACT THE GEAR. REPORTER STATED THE FAILED GEAR DOOR ACTUATOR THAT CAUSED THE AIR TURNBACK WAS SHORTER IN TOTAL LENGTH THAN THE BORROWED ACTUATOR THEY ENDED UP INSTALLING. THE ACTUATOR HOUSING LENGTHS WERE THE SAME; BUT NOT THE ROD END EXTENSION LENGTH.