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TorqueBoards 6355 motor shaft retention repair - applicable to other motors

This little how-to should apply to all current gen Torqueboards motors as well as others with similar shaft retention mounting issues. Its a band-aid fix but likely to help or last a while. \

https://forum.esk8.news/t/motor-cans-keep-coming-loose-wahhh/6113/25

The majority of the outrunner motors all being used by ESk8 share a similar weak point. The shaft is mounted to the outer can of the motor and has very little support where it does. In addition, two small m3 bolts or grub screws are responsible to hold the shaft in place. As you accelerate and brake, the rotational force being applied to the motor is 100% shared across these two m3 bolts. To make matters worse, the indent for these set screws is not 3mm when new, its larger. So there’s some slop to begin with. Some motors have better retention designs than others.

Several users have creatively fixed this issue the proper way - that is, to machine a keyway to lock the can and axle together mechanically. I don’t have access to that equipment, so here’s my solution for the time being. @b264 has a ton of great examples of work hes done to some of his hardware to fix this issue. See the post above

I started to notice a knocking and when I grabbed the motor can by hand, there was noticeable play between the can and the motor pulley. You should check your equipment frequently, the longer this goes on, the worse the repair is.


I started this journey by losing a bolt. Then realizing how fubared the other bolt already was in the seat of the axle.
Tear down revealed that the play was causing the end of the m3 bolts that bite down on the shaft to slide back and forth - the hardened axle mushroomed the ends of the bolts, wobbled them loose and was destroying the very threads they sit in. Remember, these are aluminum cans with steel bolts
The very not 3mm pockets that the bolts sit in:

Heres the motor that ive never had issues with – you can see how mushroomed the heads of the M3 bolts are.

STOP, if you’re doing this on your own and you’re meeting resistance trying to remove these M3 retention bolts, stop. The mushroomed end of the bolt is creating the resistance as you destroy all of the m3 threads in the pocket you are removing it from. You should screw them all the way in as I did, then use a small file to reduce the diameter to less than 3mm and then extract them.
We are going to be cutting new threads, but don’t make the job harder for yourself. The walls of this are very thin and there is little margin for big mistakes.

Okay so we see the problem, we dont have machining equipment to fix it…

  • 3mm or 1/8" drill bit and drill
  • A quality M4 tap – best quality you can. Because of the small space that these holes are in, I had to use a cheap M4 tap set that had a smaller overall shaft/shank diameter. My nicer taps got fatter right above the cutting area and that prevented me from approaching the hole to cut straight.
  • cutting oil, WD40, whatever. We are cutting aluminum with steel, so this will be relatively easy. However, because we have aluminum, its very easy to just destroy all of the threads as you try to create them.
  • M4 x12mm grub screws - do not use standard bolts. The clearance of the bolt head is extremely low to the motor just beneath the can. A socket head bolt may work, avoid pan heads. I would strongly recommend the grub screw approach.

So now that you have safely extracted the stock bolts. The axle is out and the can is clean, youre ready to move on.
Drill out each hole to 3mm or 1/8". The shank on the bit I was using dropped to 2.7mm after the cutting area so this was perfect. *Do not attempt to drill straight across both holes. Mine were not well aligned. Dont assume yours are. *

Next, start working your M4 tap into the material. If you’ve never used a tap, watch a few videos on it. Consistent pressure until you get a few threads cut is the key. Then you can back off a little and start working back and forth. Clear the chips frequently as they accumulate quickly and are tough to clear on these smaller taps. Use some oil to keep things moving well. Remember, the most importantly thing is keeping the tap handle perpendicular to the hole in all planes as you get the first few threads and such cut. For aluminum and such a small hole, getting out of alignment could mess up a good bit of your threads. The harder you have to push, the easier it is to get out of alignment. Don’t use power tools here.
Same as before, when that tap hits the other side. Run it all the way through until you can use your spray lube to blast off those shavings so you don’t marr the threads draggint them back up through it. Patience is key in preserving these soft aluminum threads

Clean everything well. Now is a good time to battle harden if you havent already.
Install your 12mm M4 grub screws with Loctite and allow to cure. Hoping these hold up for a bit

When re-installing, there was a shim under the snap ring clip. Place the shim over the axle, then install the snap ring. Then push the shaft (motor pulley side) from the snap ring side toward the can. Now snug up the retention bolts on either side. That shim and the retention bolts likely maintain some pre-load on the inner bearings with that pressue.

Ill come back and add if I’ve forgotten anything :beers:

Bill

9 Likes

This is a great thread. Some ways I have mitigated this same issue, which I’ve had on every esk8 motor regardless of brand. Though some brands are better than others with this, the new TB6380 motors have 4 bolts in lieu of 2, but I still haven’t tested them enough to report anything


I’ve been pinning all my motors with either 1) roll pins, 2) keys, or 3) dutch pins. The dutch pin and roll pin work better than the key way as they hold against slip in two axis (rotational and shaft sliding) instead of just one. The dutch pin (3) seems to be the best.

  1. roll pin

  2. key

  1. dutch pin

source1
source2

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That looks like a difficult machining task to put that dutch pin between hardened steel and aluminum

Any motors do better than others? I believe the Maytech sealed motors have an extra bearing there, but not much else to mitigate these issues?

I saw the pics of the larger 6380s with the 4 bolts, heres a pic @torqueboards sent to me.
image

The windows are not machined out on all 4 sides, making this very difficult to do on the 6355 cans

3 Likes