We have balanced the component well within the tolerance. still at assembly, our vibratıon levels are not satisfactory. What is the reason?

Dynamic balancing is an operation of making the center of gravity of the rotary mass in line with the axis of rotation to reduce the centrifugal force and resultant couple which are the main causes of the vibration. In case, you have used an adopter with a bore clearance of 20 micro meters and balance the assembly to G 6.3 grade, in effect your assembly when reassembled may have a balance quality of G 15 or G 20 grade. So you will not be achieving the quality grade of balancing in assembly, what was apparently achieved on the balancing machine. Similarly, the quality of bearings also plays a part. Both balancing machine and tooling is important for good results.