Hi,the motor only spins on it's axis when the platters spins up apparently to compensate for the torque needed to start up the very heavy plater. Once up too speed it stabalises & remains in place.If you put the outer platter on upside down,which Roksan have provided the lip cut-out on the underside exactly for this purpose,you can see the motor spin to it's maximum extent & then gradually return to it's original position, assisted by the return spring, as the platter reaches a stable speed.With the platter on upside down you can also check that the belt is running true.Quite a neat solution.

Apologies if seeming to tell you what you already know but may be of benefit for others less well acquainted with the idiosyncrasies of this design.