Wednesday, December 21, 2011
How to Re-wire a Potted Motor, Part 10: Motor Brush Removal
In preparation for removing the armature and cracking the motor open, we're now going to remove the two motor brushes. For those of you with no electric motor experience, they’re not “brushes” in the conventional sense; they’re little sticks of carbon that look like charcoal sticks. They reside in a tube leading into the motor and are covered by caps. There is one on the top of the motor, one on the bottom. And as you'll see, inspecting them can provide a good warning as to whether you'll be able to save this machine or not.
Here we see one of the motor brush caps. This is one of the few parts on a vintage Singer that is not made of metal, but is instead made of Bakelite, a pre-cursor to plastic. That means these are easy to break by either using the wrong size screwdriver bit or by overtightening it.
A Brownells bit #270-6 will fit it perfectly, and that is the only one I recommend using--particularly if the cap is already stripped. (More info on screwdrivers here and here.)
After you remove the cap, the spring that is attached to the brush should pop out a little. Inspect it--this can provide our first warning that something may be wrong inside the motor. The spring should be clean. If it’s dirty, that’s not good.
Zooming in, we see this spring is not clean and has some bits of oily gunk on it. That’s bad. It means grease or even worse, oil has made its way into the motor, possibly supplied by a previous owner who didn’t know what they were doing.
On the other side of this machine, we see an example of a motor brush cap that someone has partially stripped. I am still able to get it off by using the correct bit and pressing it hard, but not too hard, into the slot as I unscrew.
Once the cap is off, we get a nasty surprise:
Some unknowing soul (in my first draft, I used much rougher language) has put GREASE into the motor tube. That’s very, very bad, and a sign that this motor may not be salvageable. If you find something like this, chances are high that this motor has been completely ruined and that you will not be able to save it. Later we shall see.
Still, to quote "La Beef" from True Grit, "The Texas Ranger presses on."
Here I'm working on yet another potted motor, this one with clean springs and I'll use it to illustrate the next step. Once you’ve got the motor caps off and the springs present themselves, see if you can GENTLY pull them out. If the spring gives you any resistance and does not want to come out, STOP; if you deform this spring, later when you put it back, it can drive the brush into the commutator with too much pressure, digging a channel into it. If you don’t know what I mean by this now, you’ll see later. The bottom line is, don’t take it out if it doesn’t want to easily come out. (The grease-filled springs you see above, by the way, did not want to come out. We will deal with those once the motor is open.)
If the spring does come out, great; and hopefully it brings the carbon brush with it. (If it doesn't, don't worry, we'll get to it.)
The carbon brush will probably be covered in its own grit, which you can wipe off on a napkin or paper towel as a way to clean it. Don’t put anything else on it or use any solvents, just wipe the dust off.
Store the brushes and caps someplace safe, we won’t be needing them for a while.
If you have a machine where some unknowing soul put grease into the brush tube, don’t forget to clean that cap off and get all of the grease off of it. You don’t want that getting back into the tube after we’ve cleaned it out.
Go on to Part 11: Armature & Worm Removal