Kato motor brush reassembly

[bigdawgks]

I recently did a DCC install on a Kato ABe 8/12 Allegra, and due to the very tight space I had to solder the motor wires very close to the brush caps. I found that the heat caused both caps to actually pop out of the motor. It seems they were sealed in with some sort of adhesive goo (or maybe some type of gasket? Hard to tell what it originally was). I am not used to working on these motors (or any motors really) but I did manage to reassemble them, but now the caps are very lose inside the motor housing and the only thing holding them in place is some kapton tape I wrapped around it.

So my question is, has anyone else encountered this before and have any recommendations on how to re-secure the brush caps in place? With my current fix the electrical contact is not reliable and sometimes the motor stops working, so once I muster up enough courage to disassemble the unit again (which is a massive PITA) I would like to know how I can best fix the motor.

[mmagliaro]

You should never EVER solder to the brush caps while they are still in the motor (but you probably already realize that now, ha ).
I am not familiar with that motor, can you post a photo of it?
If wrapping a piece of Kapton tape tightly around it to keep the caps in place does not provide reliable electrical contact, I suspect that more got damaged than just the plastic that holds the caps in. 

[bigdawgks]

Not my photo (mine is not disassembled currently) but here's what the motor looks like:
https://www.masquetrenes.com/wp-content/uploads/Digitalizacion_Automotor_ABe8-12_Alegra_18.jpg

I wasn't actually trying to solder to the caps themselves but to the base of the contact strips. But yea, it turns out that's not exactly practical without disassembly. The motor does run fine when I keep some pressure on the caps, but the tape is not enough to keep them fully in place since they are just about flush (and if anything slightly recessed) with the cradle. Either way, it seems trying to take the caps out beforehand (something for which I'm still not sure what the appropriate method is) would have resulted in the same issue.

[peteski]

The photo you found unfortunately doesn't really give a good view of the motor, but from what I see, it is not a motor I have ever worked with.  However, it appears to have a standard Kato motor construction.

Yes, as Max mentioned, what you did is a no-no.  The brush-end of the motor is made from a plastic which has low melting temperature.  I have successfully soldered wires to the the thin plastic contacts near the brush holder, but I had to make sure the strip was very clean, applied a bit of flux to it, then quickly applied some solder to it. Then I used pre-tinned wire and again very quickly soldered to pre-tinned wire to the pre-tinned strip.  Each soldering operation took about a second (not long enough for the brush holder to get hot).  But I would still not recommend this process to others.

The brush holders in this type of a motor are retained by pressure. The brush holder and the opening in the plastic have ridges that snap together. Once heated the plastic ridge will soften and expand so it no longer retains the brush holder. If the brush holder is hot enough, it will cause the entire opening in the plastic piece to expand.

I don't see any really good fix for that (other than motor replacement).  A workaround would be to do something to get the brush holder to fit tightly into the hole in the plastic part.  Kapton tape Max mentioned might be one possible solution.  Or use CA to glue a strip of paper around the brush holder to increase its diameter.

[bigdawgks]

There are plenty of additional photos from the source I posted above. In fact, this guide even shows removing the brush holders to solder the motor wires almost exactly how I did:
https://www.masquetrenes.com/digitalizacion-automotor-allegra-abe-8-12/

So if how you described it is correct, it sounds like these brush holders were not designed to be removed and subsequently reassembled. If that is the case I'm not really sure there was a better outcome. The wires needed to be attached right beside the caps or they'd have been crushed by the frame upon assembly. Kato really made these things a challenge convert to DCC.

I do think adding some material to make it more of an interference fit could work. I should try translating that guide I linked to see what the author did; though it does look like they too have just used some tape to hold them on. Presuming I were to just glue them in place, is there a particular type of adhesive that would be suitable?

[peteski]

I just looked at the single photo you originally linked too.  So that web page actually shows how to install a decoder and it also shows that the brush holders were removed for soldering the wires to the metal strip.  That is the only recommended way, but as I said I has been able to solder wires to trimmed strips if I did it quickly the way I described.



Now that I got a better look at the motor, it looks like the smaller Kato motor used in the NW2 or GS-4 locos.  They are in stock at Kato USA.  You might have to swap the flywheels.

[mmagliaro]

As for removing these, you can usually remove these type of brush holders by just carefully prying under the cap with an Xacto blade or a small screwdriver.  They will snap out and snap back in just fine.  It's the heat that did you in.  It looks from the photos in that other project you linked that he popped the holders out before soldering the wires on.

If a tight wrap of tape won't do it, you are probably looking at replacing the motor.
But you can try a few things to see if you can "get away with it"...

Pop out the holder, and see if you can apply some flux to the barrel, and hit it with a quick smear of solder around it in a few places.
You can dress them with a file afterward if they get too messy.  That might increase the barrel diameter a little so it grabs firmly when you press it back into the motor.  The trick will be making it just big enough to grab tightly, but not so big that you can't press it in.  If you overdo it, you can sand off the solder a little and keep trying.

I am actually surprised  the tape won't hold them well enough to maintain contact.  The brushes have springs on them and should be pretty forgiving.  Hmmm Are the springs okay?   The heat from the soldering iron can also cause the springs to collapse and weaken.  When you press the holders in, do the springs push them back out much if you don't hold them with your fingers?

[bigdawgks]

Thanks. I actually suspect that my reliability issues are down to the fact that my wires are soldered to the base of the contact strips (the square ones that the brush holders clamp down on), and while the brushes maintain contact fine, there's not much pressure forcing the bottom surface of the caps against the contact strip. I figure soldering the wires directly to the caps (with them removed of course) will fix this. And if I can't correct it at least I have a solid backup plan of replacing the motor and properly disassembling it.

[bigdawgks]

Ok, so I finally had a chance to disassemble the power car and make some adjustments. It was a lot more difficult than it really needed to be as I wanted to keep every wire in place (and there's virtually no slack on any of them because all the electronics just barely fit in the space I have them in). I ended up soldering the pickup plates to the caps to prevent any loss in continuity between them. The kapton tape around the motor is indeed enough to ensure the brushes function reliably (and also prevents them contacting the metal frame), so no other changes seemed necessary. Reassembly was also tricky again due to carefully insert all the pieces around everything without disturbing the wiring, but in the end it was probably still easier than trying to re run and connect all the wires. I had some initial reliability problems with track pickup at first but after some tinkering to try to find where the problem was it simply went away.

I plan to run the train at a show next weekend so I'll find out then how well it all holds up.