After you remove the housing and weight, take out the brushes.
Remove the two screws (3 in older models) that hold down the armature electrical plate. I had to remove the screws that hold the chassis to the motor assembly. Notice that the armature is pretty dirty.
Clean the armature with acetone. Alcohol works too, but not nearly as well.
It's important to remove dirt from between the three armature plates. Otherwise, there is electrical leakage between the connections that keeps the motor from running full speed. Clean the three cracks with acetone.
Most of the time, this is level of cleaning is sufficient. But, this engine has been used for about 10 years and the armature has grooves. This works okay, but you'll need to clean it more often.
If necessary -- and if you dare -- polish the armature with #600 sand paper. I do this by putting into a power drill that's held in a vise.
This step only needs to be done every 5 to 10 years of moderate use.
As you can see, polishing makes a huge difference!
Clean the old oil from the gears. It can get "sludgy" in older engines. The previous owner had used some type of automobile grease that was way too thick for these tiny gears.
I like to use Fleischmann oil on the shafts and bearings. If you use a different brand, make sure it is "plastic safe" oil.
Don't over-oil -- it will just make the wheels and tracks dirty.
Apply a small amount of oil to the motor shaft bearing. Too much oil here will mess up the armature after very little running time.
I like to use the thicker Roco lubricant for the gear's teeth.
Clean the brushes on a piece of paper. They usually don't need to be replaced.
