"From another SkyMaxx post"
Setting gear mesh is very important to the longevity of both gears and the components driving and being driven by the gears.
Here's how to do the mesh check.
1. Loosen the screws that hold the motor mounts to the chassis plate (don't take them all the way out).
2. Make sure you have both spur gear and clutch gear on properly (since you've mounted the spur and the clutch is attached to the motor, you probably have little to worry about here).
3. Take the plastic bag that the spur gear came in (a ziploc bag will work just as well) and place one thickness of the plastic between the two gears.
4. Push the motor back into place so that the two gear compress on the plastic.
5. Tighten the motor mount screws (making sure that the motor mounts are as square to the chassis as possible...you want the gears to have as even a surface to surface contact as possible).
6. Pull the bag out. The gears should rotate freely and mesh together just right.
Hope this helps...