[gpetilli]

The two middle gears have a hub spacer on one side and not on the other. Make sure the two flat sides are against each other and the two spacer sides are pushing on the inner races of the bearings.

Other than that, there should not be an issue with the retaining screws being a bit loose.

We had problems last year with a student who held the box in a vice while she worked on it and introduced a bow that caused the CIM motor not to mesh well when its screws were tightened. We wound up shimming the motor to reduce the gear engagement.