Armature play

[Bandini]

I have a GM Dr. Speed 21 turn modified, and last weekend something happened to it, because now there's a lot of play in the armature. I never noticed any play when it was new, but now it's something like 2 millimetres.

I opened the can to have a look, but I can't see anything that looks broken. I've never owned or looked inside a modified before, so I'm not sure what to look for, though.

There are two thin shim washers and a "pertinax shim" on the comm side, and one shim washer on the pinion side.

My first question is; what could have happened to it?

The "pertinax shim" fits rather tightly on the axle. Could this have been the only thing that kept the armature in place? In that case I guess I just need a new shim, because this one isn't tight enough anymore.

My second question is; how do I fix it, exactly.

I guess I need to shim it quite a lot, but I'm not sure how. If I drop the armature down in the can, the laminations go a couple of millimetres below the upper edges of the magnets. Is that normal? Is it important to somehow center the armature on the magnets? I guess I'm just asking what side to shim, the comm side or the pinion side?

What kind of shims should I use? There must be a reason why there are two different kinds to begin with, metal and "pertinax".

Any help much appreciated.

[Railman]

My guess is that either one or both of the ball bearings wore out or the plastic thrust on the gear end of the armature wore down due to a heavy thrust against it. That's all I can think of. Is it really 2mm? That's a bunch!
Joe

[Bandini]

"A heavy thrust against it" sounds like a good guess. I noticed the play when I superglued the cracked motor mount...

The ball bearings look OK. I'll have to look closer, but I think they are.

"The plastic thrust", though. I didn't even know there was one, but looking at http://www.team-orion.ch/motor-faq/part3.asp I can see what you mean (even though my armature isn't Team Orion). That could definitely be it. It looks about the same size as the amount of play I have, and the gear end seems to be where the problem is.

I'll have to open the motor again, and see if I can find the plastic thrust squeezed into the windings somewhere.

Nervously; are plastic thrusts something you can buy, or is my armature junk now?

I haven't actually measured the play, but it's easily more than 1 mm.

[Bandini]

It looks like you're right, Railman. The white plastic thing looks deformed and is jammed into the windings.

It looks like I could use shims instead of the plastic thing, but there's got to be a reason why they put the plastic there in the first place.

Is it perhaps meant to protect the motor from heavy thrusts? In that case, I think I'll need some more plastic.

[Railman]

Bandini, Try using a few teflon shims up against the melted plastic
& then finish with a brass shim up against the bearing. Was there a brass or steel shim up against the bearing when you took it apart? If not it may have been what caused the failure in the 1st place. Just shim it in like Jeep said & it should work out ok for you. You might also want to check to make shure that the bearing is seated all the way in in the can. Maybe it wasn't & maybe that's why they left out the shim??? Or maybe the bearing drifted out & caused the excessive wear? Just guessing here. Good luck.
Joe

[Bandini]

There were metal shims against the bearings on both sides. I've looked closely, and I'm pretty confident that the plastic is the only thing that's damaged. The bearings and everything else looks good.

Teflon shims sounds like a great idea. Come to think of it, I've heard a tip once regarding slot cars, to shim those with teflon, brass, teflon, brass etc. Sounds reasonable. Do you think I should try that here?

Is there any good way to know when the arm is centered in the magnetic field? Otherwise I guess I'll just add shims on the gear end until the play is OK, as I don't think anything's wrong on the comm end.

Big, big thanks Railman & jeepinator!

[Bandini]

jeepinator: The Tower website isn't clear on this; is the Trinity Motor Spacer Assortment teflon or metal?

I noticed something else. Both Trinity and Peak Performance say their teflon shims are meant for motors that don't have ball bearings. It's not that I don't trust you when you tell me to use teflon, but I'm having trouble finding teflon shims here in Sweden, and Tower takes weeks to deliver here. Do you think I would damage the motor if I used brass or steel?

[TSR6]

Originally posted by jeepinator
Yes, go for metal shims, and yes the Trinity kit is metal.

Accually, unless you are talking about different shims, the Trinity ones are teflon. The #4030 kit is definately teflon.. I have the package sitting in my toolbox. :)

-Troy

[TSR6]

Jeep - They must have changed them not too long ago. The #4030 are definately teflon ( per my toolbox and package labeling.. hehe ) and i searched Tower "Trinity Teflon Motor Shims 12-Piece "... so they must have changed it around, or maybe discontinued the metal ones ( ? ).

-Troy