A B737-300 WAS DISPATCHED IN NON COMPLIANCE WITH THE NOSE GEAR PINNED IN THE DOWN POS. CAUSED BY A SUBSTITUTE GEAR PIN INSTALLED DURING MAINT.

Narrative

ACFT X CAME INTO ZZZ FOR OVERNIGHT MAINT (ROUTINE). ONE DEFERRAL ON THE ACFT WAS A FAULTY GPWS. WHILE TROUBLESHOOTING THE SYS PER THE MAINT MANUAL; ONE STEP WAS TO INSTALL GEAR PINS. NOT HAVING ANY IN THE IMMEDIATE AREA I CHOSE TO USE MY 6 INCH 1/4 INCH DRIVE RATCHET EXTENSION FOR THE NOSE GEAR DOWN LOCK PIN. AFTER ALL THE TROUBLESHOOTING AND TESTING PER THE MAINT MANUAL; I RETURNED THE GPWS BACK TO AIRWORTHY CONDITION AND RELEASED THE ACFT BACK TO SVC; FAILING TO REMOVE THE 6 INCH EXTENSION FROM THE NOSE GEAR DOWN LOCK ASSEMBLY. UNFORTUNATELY; THE ACFT WAS UNABLE TO RETRACT THE NOSE GEAR AFTER TKOF; THUS RETURNING TO THE AIRFIELD; BACK TO THE GATE. AT THAT POINT IT WAS INSPECTED AND THE 6 INCH EXTENSION WAS DISCOVERED IN THE SPECIFIED AREA. CONTRIBUTING FACTORS TO THIS EVENT ARE: POOR CHOICE IN NOT FOLLOWING MAINT MANUAL PROCS; MAINT WAS ACCOMPLISHED AT THE GATE OVERNIGHT; THUS LIGHTING WAS INEFFICIENT; FRUSTRATION IN TRYING TO FAMILIARIZE MYSELF WITH THIS SYS SO AS TO FIX IT DUE TO THE FACT THAT IT WOULD BE GNDED AT THE END OF THE FLYING DAY (MY SHIFT STARTS AT XA00 AND I LEAVE AT XK15; I REALLY TRIED TO PUT A FULL EFFORT INTO FINDING THE FAULT).