the gear mesh CAN be set at the factory...but its always good to double check it before running it....whenever I get a new rc I always check the mesh, and adjust if needed...then I remove one screw at a time (I do it in a x pattern but thats just me) and then put lock tite on the screws....after awhile u will get the feel of what the mesh should be by holding either the spur or clutcbell and rocking the other...

as far as a clutchbell not spinning freely when tightening the screw....never happened to me on a new rtr but I assume its possible....that would be a shimming problem