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Old 04-24-2007, 03:21 PM   #1
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Default How to shim motors

Whats the general idea for shimming motors and how do you know which end to use the shim? Do you look at the comm wear?
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Old 04-24-2007, 03:52 PM   #2
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I learned that you want to center the arm within the magnetic field. So put the arm in the can without any shims, then put the hood on without screwing it down.
Now spin the arm by grabbing the output shaft and spinning it quickly. When it stops spinning pull on the shaft and the distance it goes before stopping on the bearing is the space you need to fill with spacers. Once you get that sorted out you need to shim the top to eliminate any remaining slop, but it's better to have a slightly loose situation than a tight one that will create drag.
Always use the large fiber shim on top to protect the comm. from oil. Also I've found that you want different material shims on hand. You should not use metal or brass shims on a motor with bushings. And you should not use plastic shims on a motor with bearings.
Lastly be careful. If you are using metal shims the magnets can pull them off when you are installing the arm. If you don't notice it this can do big time damage to the motor.
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Old 04-24-2007, 08:44 PM   #3
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yes Fish is on it. but from Birdman i was told that the most important part was to have the brushes centered on the comm. as this is where the juice i delivered and also the point where you will see the most wear. if it is not centered it will hit the prongs that hold down the windings, or if out to far it will hit the shim. mostly the motors come from the factory centered on the comm. and an aftermarket motor is even better set-up. but do look at the comm the first tear down and notice the wear and that will help you keep things in line. also with a quality built motor when your comm is centered your arm is also centered. also remeber you want a little play in your arm in the motor can just like gear mesh. and that is very important in stock motors since they run bushings and not bearings. in a bearing motor you can tighten up you play just a bit, a very little bit. that way the comm stays and the arm stays as close to center as possible without burning up your motor. i wish there was a better way to explain it from me. but if you have more?'s then go to Birdmanmotors.com and email him. his name is Dennis.
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Old 04-25-2007, 01:59 AM   #4
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What is the recommended end-play for a motor?
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Old 04-25-2007, 02:03 AM   #5
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when i did slot cars keep in mind little smaller not sure if it will be the same here but when i built motors i kept the motor play down to about 2 thou. i would suspect that you might want a little more then that prob. no more than 5 thousandths play
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Old 04-25-2007, 09:59 AM   #6
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I never actually measured the end play. It was always just a feel thing to me. I would say it should be as close to none as you can manage. I always had a good selection of different thickness shims. Once I had the arm centered and shimmed on the bottom I would start shimming the top. Basically I would put them on and stick the hood on and spin it. If it was free and there was some gap I'd try to add a little more. If there seemed to be some drag on the arm I would try a different combination of thickness of shims in order to get rid of the drag while still being close to no end play. Trial and error and fiddly, but effective and I never damaged or burned up a motor.
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Old 04-25-2007, 11:04 AM   #7
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Thanks guys, the reason why I ask is because I have a Checkpoint Money motor that seems to be wearing at the top of the comm. I was going to try to move it down, but one of the shims at the top is actually a thick little rubber o-ring.

Any ideas?
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Old 04-25-2007, 11:13 AM   #8
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I have noticed that Checkpoint uses those o-rings. Probably a kind of shock absorber thingy (technical term). I have also noticed that the new generation motors are more critical to positioning relative to the comm. and brushes. I have seen a couple Revolution motors where the wire tabs on the arm. were smacking the brush guides on the hood. Seems to me that positioning guidelines should still apply, just that there is more to pay attention to.
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Old 04-25-2007, 11:54 AM   #9
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Quote:
Originally Posted by mfishel
I have noticed that Checkpoint uses those o-rings. Probably a kind of shock absorber thingy (technical term). I have also noticed that the new generation motors are more critical to positioning relative to the comm. and brushes. I have seen a couple Revolution motors where the wire tabs on the arm. were smacking the brush guides on the hood. Seems to me that positioning guidelines should still apply, just that there is more to pay attention to.
So should I move it to the bottom?
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Old 04-25-2007, 12:39 PM   #10
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I would start with the already mentioned guidelines. Get the arm. centered relative to the magnets. Then carefully check for clearance on the hood and then look at your brush position on the comm. I'd do it in that order. It will take a little trial and error, you may even need to install brushes and let it run in a little. But once you have it all right you just need to keep everything in order when it's time for a rebuild.
One other note is to make sure you are marking your can to indicate not only pos. and neg. but also timing. I hate it when I go to put my motor back together and I forget which end is up!
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Old 04-25-2007, 12:50 PM   #11
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Well you cant change the timings on the money motor, luckily haha. Im guessing I should take the o-ring out and replace it with a real shim then?
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Old 04-25-2007, 12:55 PM   #12
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Actually my guess as far as the o-ring is to leave it. I'm thinking that these new motors are machined a lot more than they used to be. I may be mistaken but that motor I believe has a machined hood as opposed to stamped pieces that are then assembled. If this is the case it likely is that the tolerances motor to motor are much more precise and therefore simply sticking an o-ring is sufficient.
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Old 04-25-2007, 01:01 PM   #13
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Ok, so in order to fix the comm wearing too close to the top what should I do? I think the O-ring really pushes the top part down, I mean its pretty thick, so if that stays should I add shims only to the bottom?
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Old 04-25-2007, 01:08 PM   #14
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In a word yes. That is if there is sufficient free play that it is allowing the comm. to drop away from the hood, and the brushes are too close to the top edge of the comm. If the o-ring is becoming compressed when you add shims then it'll bind up and that isn't good.
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