· Rich Dumas
The first thing to try is to spray contact cleaner directly onto the commutator while the motor is running at six volts or so. That treatment will remove any oil that might be on the commutator and can also remove dust that has gotten stuck in the commutator slots. If that treatment has little or no effect there may be a burned on layer of oil on the commutator that will have to be polished off or there could still be dust in the commutator slots. The next thing to try is to pull the endbell and carefully remove the brushes. In order to get at the commutator you need to remove the armature from the endbell, if a pinion gear is still in place it will have to be removed. If the slots are still full of dust you can srape them out with thin, stiff plastic, like blister packaging material. If you use metal to do the scraping you might scratch the commutator. You can use a dab of metal polish on a cotton swab to clean the commutator. It is possible that the motor brushes are worn out. These motors have brushes that are mounted on feelers, rather than using brush springs like SCX motors. A feeler may be bent so that there is not enough brush tension. It is difficult to get optimum brush tension with the feeler arrangement. Somemtimes you can swap in a brush assembly that is in better shape.