A thread started a few days ago...
Be sure that the sprocket fits snug on the shaft. The end of the shaft is slightly tapered. The bore in the sprocket is slightly tapered. Although most will interchange, just be aware that there are some odd ones out there.
If your sprocket goes onto the shaft all the way up to the bearing...and the sprocket rocks on the shaft...the bore in the sprocket is too large for the shaft.