Hi John,
Kenny forgot to explain that, but the Motor Constraint rotates around the X-Axis.
The Manual is really clear in this case:
"The rotation axis is the X axis of the object hosting the constraint. This is in contrast with the Hinge which uses the Z axis. Since the Motor is vulnerable to confusing perturbations without a matching Hinge constraint, special care must be taken to align the axes. Without proper alignment, the motor will appear to have no effect (because the hinge is preventing the motion of the motor)."