Anything beyond changing brushes and bushings and a general cleanup is probably best left to a rebuilding shop. Machining the commutator, undercutting the mica between the commutator bars, and changing field coils requires tools and equipment the average hobbyist probably doesn't have unless his name is Denny! If the commutator isn't badly worn, a quick shoeshine with medium-grit sandpaper is usually all that's needed.
Jerry
