What was found
AS THE THROTTLES DECREASED AT TOP OF CLIMB THE AIRCRAFT DEVELOPED A SIGNIFICANT VIBRATION THAT COULD BE FELT & HEARD. THE LT ENG N1 VIBRATION WAS 3.2, ALL OTHER PARAMETERS WERE NORMAL ON BOTH ENGS. RETARDING THE THROTTLE 10% N1 IN CRUISE AT FL310 DIMINISHED THE VIBRATION TO 1.7 N1. DIVERTED AT THE REQUEST OF GOC. PERFORMED NR ENG TRIM BALANCE IAW MM, FOUND WRONG BALANCE WEIGHT PN & HOLE BLADE NRS ARE SELECTED AT MAT. CHANGED PN & HOLE BLADE NRS TO ACTUAL CORRECT NRS. RUN ENGS & PERFORMED ENG VIB & RELOCATE THE BALANCE WEIGHT. RUN ENGS AGAIN & GOT FOLLOWING DATA 0.2 AT N1 76%, 0.3 AT N1 SERVICE.