Motor Brushes Wearing Out?

[tehachapifan]

I've got an older (mid-to-later 90's) 6 axle EMD diesel from one of the big 2 manufacturers that has recently developed what might be described as a loud wood planer type noise. This occurs in both directions but mostly forward. This is not the well-discussed screech that is an indicator of dry motor bearings or bearing blocks. I originally thought the motor was starting to make contact with the shell itself as that's what it really sounds like (and there's some curious vertical black marks on the inside of the shell where the poles spin), but it also does it with the shell off but much more quietly (the shell must be really amplifying it though). Wondering if the motor brushed have worn out and maybe the spring is making contact with the commutator? Not really wanting to tear apart the motor to look in fear of having an unscheduled spring launch if that isn't what it sounds like it is. The loco seems to run fine for the most part but it will occasionally stop running suddenly and will also sometimes not start again after a stop (no lights either). I know this behavior sort of sounds like a lost pole but, as I mentioned, the lights go off too (my experience with a lost pole is you still get lights in a DC loco). Thoughts?

Thanks!

[avel]

I've popped these brushes into Atlas and Walthers engines. They come with springs too.

http://www.modeltrainstuff.com/Kato-N-Motor-Brush-Set-p/kat-927010.htm

[victor miranda]

I'd go inspect...

motors fail a lot of ways and I am not sure what the lights out means.
either is is not power to the loco
Or
the motor is in a shorted condition and is hogging the power.

a set of brushes is 3-4 dollars
if the commutator is destroyed it is 25 ish dollars.

go looking.

victor

[mmagliaro]

Yep, you have to pull out the brushes.  It could be a worn out brush, it could be a broken piece of brush lodged in the commutator slot, or just lots of carbon build-up in the slots.  Or it could have nothing to do with the brushes at
all.  I'd pull them out, clean the commutator slots out using the tip of a tooth pick (NO METAL!) maybe dipped in some alcohol, followed by a soft brush, - just repeat with clean toothpicks and keep cleaning the soft paintbrush
out until you get all the black junk out of the slots.  After you clean it, if the brushes look okay when you pull them out, put them back in and observe.

Cleaning the commutator can be very important.  They can really fool you into thinking they are "not too bad", but clean it to be sure.

[tehachapifan]

Thanks for the replies! Interestingly, the buzzing noise has suddenly stopped or at least lessened significantly. If and when it returns I'll take a look at the brushes.

[mmagliaro]

I thought of another possibility. 

One of the magnets may have broken loose from the inside
of the motor frame.  That has happened to me.  When it does, the motor
can gently graze the spinning armature, making a buzzing noise.  Surprisingly, this doesn't always
make the motor just quit running.  The magnet might just move a little,
and sit in a bad spot inside the motor frame, where it makes noise.  And the magnet will move
around while the motor runs, so the noise can come and go.   Something to check the next time you have it open.


If if has happened, you can slide the magnet out, scrape the back of it and the frame mounting area clean,
then put some 2-part epoxy on it and slide it back in.   Then use clip leads to put power to the
bare motor (removed from the chassis), so you can squeeze the magnet up into position with your fingers
 and observe the motor running.  When you get into a sweet spot, apply a few drops of ACC into the joint between
the magnet and the frame (it helps to have an assistant for this!)

If you have an ammeter, that really helps for determining when the magnet is in the ideal spot.
The best spot is when the amperage is at the lowest you can get it.  If you don't have a meter,
you just have to wing it judging by how quiet and fast it runs (quiet and fast = good, noisy or slower=bad).

Hold the magnet in position while the motor is still running well, until your fingers ache.  You have to let the ACC get
hard so that you can let go and the motor still runs well.  Then you can let it sit until the epoxy sets up.  The ACC is just a "tack' to keep the magnet in
the right spot while the epoxy hardens.

[peteski]

If as indicated the lights go out (assuming the lights are standard design DC headlights) then that is a problem independent from the noise.  Headlights are wired in parallel with the motor so the motor not working should not affect the headlight operation. The only way I can see the motor affecting the headlights would be if the motor is becoming a dead short (internally). That would short out the voltage from the rails to both the motor and the headlights caught them to go dark.

[mmagliaro]

True: I forgot what he said about the lights   

I think I'd keep picking at the motor and the pickups
 to figure out what the problem really is.  Problems that "go away by themselves"
always come back by themselves.

[Doug G.]

If there's enough conductive material in the slots, however, it can conduct between the two brushes, draw a lot of current, and extinguish the lights.

Rare but possible.

Doug

[djconway]

one tip to avoid the springs going into low earth orbit ---> disassemble the motor inside a 1 gallon plastic bag.

[Doug G.]

You would think that, after over 50 years of working with small OOO/N scale parts, I would have learned to do something like that but I still spend more time than I liike to on the floor with a flashlight.

Doug

[ristooch]

one tip to avoid the springs going into low earth orbit ---> disassemble the motor inside a 1 gallon plastic bag.

Huge plus 1! That is simply a great idea. Naturally one would want to reassemble the motor in the bag also.

Sincerely,
Paul Ristuccia