In taking apart on old junker motor that apperas to have gotten too much oil and other junk inside it from a past life… when I got everything cleaned up and back together then brushes seem to immediately ‘dirty’ the commutator. I used a points file to dress their surface and cleaned them in alcohol and allowed them to dry but they just seem to stay well, ‘dirty’.
Like I said maybe they just need to be replaced but I’m curious if they were exposed to too much oil, dirty, grease if brushes can become ‘ruined’?
They can indeed become oil impregnated. I know of some people who have sucessfully cleaned them, however I’ve found just replacing them to be the easiest thing to do. As I recall, the last time I bought brushes, I paid about $.50 a set. This won’t buy the solvent that you need to clean your old pair.
Keep in mind, though, that the crud you’re seeing could just be the result of normal operation. They’re basically just big pieces of pencil lead, and even a single rotation of the commutator can leave black lines on it.
As ben suggested, just replace the brushes, but I would also replace the springs as a worn/weak spring will give you trouble and for the cost, it beats taking down the engine again and diagnosing the problem.
Even brand-new brushes will leave marks on the commutator, some more, some less depending on the makeup of the brush material. As it was explained to me, as the motor spins, friction between the brushes and the commutator deposits a microscopic coating of graphite from the brushes onto the commutator, thus eliminating most subsequent friction and contributing to a long, healthy life for the commutator. Clean it off, and friction will imediately wear loose another layer of protective coating, as it were, and deposit it right back where you think you don’t want it.
Having said that, I have firsthand experience with oil-soaked brushes leaving a mess on the commutator. Brushes are cheap, so in this case I just replace them. I have never successfully de-oiled oily brushes.