The part of the HD reverse motor that gives it the power to turn the gear housing is called the armature.  An armature is nothing more than copper coils of wire wound around a stack of iron ore core. When attached to a commutator and copper graphite mix brushes, the power input causes one portion to be pulled towards a magnet while simultaneously the coil on the other side is repelled. As the commutator turns the brushes make contact with the next bar and the process repeats itself as it becomes a rotation.

As the brushes start to wear, or the spring tension is depreciated due to overheating or pollutants, the pressure that the brushes ride on the commutator is weakened. This leaves arc or tracking on the commutator. Also stress for overheating. Eventually a very common affliction with the commutator is a dead bar or dead spot.

Most users will have no idea this is happening because there is virtually no way to know damage is occurring.

But after usage continues, the heat on that particular weak bar worsens each time it passes a brush. Soon the bar will be completely dead, and is un rebuildable. The copper is pitted and worn down past the point of saving. You have to have a new armature.

For the HD reverse motor, as in many magnetic housing planetary gear reduction style motors, this is a fairly common occurrence. Armatures that pass our 110V and growler test criteria (although not  many) are sprayed with an insulating varnish and dried in a booth. The ignition sealer insulating varnish is sprayed both on the metal laminations to protect against corrosion, and the insulated copper windings for additional electrical protection against shorts. The commutator is then tested for run out(roundness) and polished on our lathes.

This is process in itself. First, we start with a medium file, and quickly move to 80 grit sandpaper. As the glue in the sandpaper cannot be allowed to impregnate the copper in the commutator, all finish work is done with a copper mix sanding stick. Then, all the bars must be cleaned out with tools and placed back in the lathe for a final finish with the fine grade sanding stick. This finish step is even performed on our new armatures for optimum performance.

We have learned over the years that commutator finish is the secret to an extensive brush life expectancy. The shape, precise condition and finish of the commutator itself is the principal deciding factor for brush break in. When the brushes break in properly and completely without foul, they will give you the highest life expectancy possible because of reduced spark wear and tear. This is the secret to a longer life reverse motor.