A NUT ON A THROTTLE ARM WAS NOT SAFETIED. ON DSCNT CREW UNABLE TO REDUCE PWR LEVEL FROM CRUISE SETTING.

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ON WED; I PARTICIPATED IN REPLACING #2 ENG ON ACFT X. EIGHTEEN DAYS LATER ON A FLT TO SALT LAKE CITY; THE CREW RPTED THAT #2 ENG WOULD NOT REDUCE PWR FROM THE CRUISE PWR SETTING. THE MECH THAT WORKED THE ACFT IN SALT LAKE CITY STATED THAT THE NUT HOLDING THE THROTTLE ARM ON THE CROSS SHAFT HAD BACKED OFF. THE NUT ON THE L SIDE OF THE CROSS SHAFT FOR THROTTLE CRANK ARM HAD NOT BEEN SAFETIED. THE MECH WHO RIGGED THE THROTTLE DURING THE ENG CHANGE HAD NOTICED THE SPACER FOR FUEL CUTOFF CRANK ARM INSTALLED INCORRECTLY WHICH HE CORRECTED; BUT DID NOT DISTURB THE THROTTLE ARM NUT. PRIOR TO BEING INSTALLED ON THE ACFT; THE ENG HAD A 'C' CHK PERFORMED AND THE GEARBOX REPLACED; DURING WHICH THE CRANK ARMS WERE INSTALLED ON THE CROSS SHAFT. SUPPLEMENTAL INFO FROM ACN 318254: DURING THE RIG OF THE ENG; IT WAS DISCOVERED THAT THE START LEVER CRANK WAS IMPROPERLY INSTALLED AND WOULD NOT ALLOW FULL THROTTLE TRAVEL. THE CORRECTIVE ACTION WAS TO REPOS THE START LEVER CRANK. AT NO TIME WAS ANY ATTENTION GIVEN TO THE THROTTLE CRANK. NO PAPERWORK WAS GENERATED FOR THE START CRANK AS IT BECAME A NECESSARY PART OF THE RIG. ALL SAFETIES THAT WERE DISTURBED WERE COMPLETED AND INSPECTED. SUPPLEMENTAL INFO FROM ACN 318158: THE ENG GEAR BOX WAS REPLACED. THE JAM NUT IS PART OF THE GEAR BOX INSTALLATION. I WAS THE INSPECTOR ON THE ENG CHANGE AND NOT THE GEAR BOX. I PROBABLY SHOULD HAVE LOOKED AT THE SAFETY ON THE GEAR BOX CROSS SHAFT; BUT I ASSUMED THAT IT WAS LOOKED AT AS PART OF THE GEAR BOX INSTALLATION; AND SHOULD HAVE BEEN.