A cheap DIY augmentation to torque arms for axles with flats.

[mikaloyd]

I have been trying all sorts of crazy DIY things to make sure i dont get rollouts on my cheap kit bike's front drive axle as it has slowly degraded the front fork dropouts.

The axle torques in the dropout a few thousands of an inch and eventually loosens the nuts, which allows it to rotate more and starts adding more damage leaving it with a few more thousandths to rotate and its a vicious circle that would end up as a rollout and likely crash.

The cheap chinese torque arms were not up to the task of preventing this for a number of reasons, and I was too lazy to tighten my axle regularly enough to stop all damage. I finally found Grin's torque arm and after modifying it so that it fit my bike, it may have fixed everything. But sometimes hope and confidence is not always enough to fix something for sure, and even Grin's torque arm does not directly address one of the root problems of the axle nuts loosening. So I augmented the good torque arm with a way to lock the nuts in place once they are tight just to be sure.

I drilled and tapped the nuts through all 6 flats for set screws then I re-tapped the nuts to clean up the threads which engage the axle threads. Now I tighten the nuts normally and add up to 1/6 of a rotation to align two of the set screw holes with the axle flats. Then I tighten the set crews using a little blue locktite to make sure they stay in place. So far this works perfectly. I wouldnt say this could be used instead of torque arms but it certainly augments them. It might even be enough to ave made the cheap chinese torque arms work. Anyhow I thought Id share this with the forum and listen to any comments or ideas about it.

 

[offGridDownUnder]

comments or ideas about it.

Would it work to use a locknut after the existing nut?

The idea is to install the regular nut, then thread another nut on behind it, and with a wrench hold the existing nut (which you have already tightened to do it's job) and tighten the lock nut down behind it. You can buy 'narrow' nuts to use for exactly this purpose.

You'll need to carry the two wrenches to remove the wheel if you need to repair a flat, etc. But you need to carry the wrench plus whatever loosens and tightens your set screws now.

Another approach is to use a castle nut - this is a nut with 3 slots cut across the diameter on one side, which then looks a bit like the 'teeth' on a castle wall (actually cover for archers). You tighten the nut, then select the slot that matches a through-hole in the bolt or shaft and put a cotter pin in to keep the nut from unscrewing. Or use a piece of wire to do the same - racing cars generally have many of their nuts wired to keep them from unscrewing.

Many of the motors that use flats also run the wiring through the hollow axle bolt, so you can't have a through-hole in the axle.

You still need the torque arm - that's about protecting the dropouts, not about the nut loosening.

 

[mikaloyd]

I agree that this only augments torque arms and does not replace them/

Using a lock nut is not possible in my case because there are not enough extra threads beyond the nut, unless I omit the torque arm.

Flat tires are a problem for sure. Not only for the reasons that you mention but also because a wrench long enugh to remove and retorque the axle bolts is far too big o carry and also because to replace a tube Id have to flip the bicycle upside down and then remove virtually everything holding the cable between the controller and the motor in order to have enough cable slack for my front wheel to reach the ground to replace the tube. If I get a flat which cannot be patched the dumb way of finding the hole and patching with the wheel still attached I will either have to ride home on a flat or call for help. Fortunately (well really unfortunately) I live in a place where puncture vine is rampant and goat heads are everywhere so my tires have recieved so much pre-need green slime and various kinds of anti puncture materials that I havent had a flat tire in more than three years. Which, since I said it, probably means I will get a flat within a week now. I used to have dirt bike tubes meant to be changed without removing the wheel on the trail. If I ever see them for bicycles I'll get one

Aircraft style safety wire is good but it is a complete pain to drill so that you get a hole through one flat of a nut that exits out the flat adjacent to it. You can go through a lot of 1/16th inch drill bits and nuts learning how. And then you need a stock of safety wire around and some self twisting safety wire pliers if you want it to be handy at all. It is a good idea but not for a cheap and simple hobo like me.

I havent looked around but I also havent noticed castellated nuts available for axles. I wonder how hard the axle is if you try drilling it for a cotter pin?

 

[Diggs]

Using a lock nut is not possible in my case because there are not enough extra threads beyond the nut

An easier thought - I usually resort to a jam nut in this case or a pair of jam nuts locked together since they are thin. But I tend to take the easier road and this may not work for you.

 

[amberwolf]

because a wrench long enough to remove and retorque the axle bolts is far too big o carry

You can hide one on your bike frame by ziptying it to the frame / stays under a spiral wrapping of old innertube to hide it's shape (so thieves are less likely to realize the tool they need to steal your wheel is right there).

I wonder how hard the axle is if you try drilling it for a cotter pin?

Most axles are not very hard, unfortunately (making it easy to damage the threads or the flats and end up with axle spinout).

I havent looked around but I also havent noticed castellated nuts available for axles

All you need is one that has the right thread count and diameter. Most of the cheap motors are 12mm axles. Some of the big ones are 14mm. Most are 1mm thread pitch; you can take your existing nut to a hardware store and check it's threading on their bolt/nut fit panel next to the bulk bins of nuts and bolts, then get a castellated nut that fits the same bolt yours does.

If you have flatwashers in your axle hardware stack, you can replace them with Nordlocks to help keep the nut from coming loose.

But if you have properly secured the torque arms themselves, and the arms are correctly designed so that they have *zero* play when slipped onto the axle, you could run without any axle nuts and the wheel will stay where it's put.

If your torque arms have *any* play at all when slipped onto the axle, or are really easy to get on and off of the axle, they are too loose, and will allow the axle to rock back and forth, especially if you use regen. If you have two arms you can install one so it is fully "twisted" clockwise, and the other counterclockwise, and it will help more than if they're both in the same direction, but better is to get arms you have to tap onto the axle (that fit it perfectly).

Pinching / clamping dropouts can be built for even better axle security, but are typically only needed for very high-load high-torque/power systems (such as on my SB Cruiser cargo trike).

There are a number of other ways you can secure the axle; I recommend this thread as a start:

torque arm picture thread

Cross-posting these two threads so a search will turn up both: "Found an awesome torque arm" (3 pages) https://endless-sphere.com/forums/viewtopic.php?f=1&t=11570 xxxxxxxxxxxxxxxxxxxx Original thread died. Figured I'd help out and repost what I saved. Here is the album link...

endless-sphere.com

 

[docw009]

My bafang front motor,I believe it's an SWXH, does not put the cable thru the middle of the axle, allowing me to use a torque wrench on the axle nuts.

Anyone else using torque wrench? What are your values?

I'm around 25 ft-lbs on the Bafang. For soft steel, like grade 8.8, I've seen 70 ft-lbs quoted for 14mm-1.25 and 38 ft-lbs for 12mm-1.25. However, our axles are 12x10 with only half the thread being used. When I do my other hub motors by hand, I found I would set them around 20 ft-lbs. SInce they have hollow axles o one side, perhaps that is enough, I've never seen the nuts move either. They're marked with a sharpie pen, Ditto for the Bafang front motor,

I also have a torque arm on one side of the bafang by the rotor, but they didn't make the axle long enough to do it on the other side.

 

[offGridDownUnder]

As this is a thread about torque arms, and others seeking may view it, I'll mention that Grin has just come out with a slew of new designs to accommodate some of the problems mentioned here, including one that deliberately clamps down on axle flats to preclude any movement:

Torque Arms - Ebike Parts - Shop

We now have a full range of 7 torque arm models in production that together fit almost all front/rear 12 and 14mm axle motors, along with special ones for regen braking use. We also offer motor-specific arms for the Grin All-Axle and GMAC motors.

ebikes.ca

 

[mikaloyd]

As this is a thread about torque arms, and others seeking may view it, I'll mention that Grin has just come out with a slew of new designs to accommodate some of the problems mentioned here, including one that deliberately clamps down on axle flats to preclude any movement:

Torque Arms - Ebike Parts - Shop

We now have a full range of 7 torque arm models in production that together fit almost all front/rear 12 and 14mm axle motors, along with special ones for regen braking use. We also offer motor-specific arms for the Grin All-Axle and GMAC motors.

ebikes.ca

I like everything about the regen torque arm except one. Hose clamps that hold down the anchor point of the torque arm.

 

[amberwolf]

You can always use something else to do that part. There are frame-specific clamps for various IGHs' torque arms or those from coaster brakes that can be adapted for this purpose, or one can be custom made, or if the arm end coincides with the right point(s) on a frame, you can bolt straight thru the arm into the frame. (might have to drill a hole in the arm in the right spot to match/line up).


FWIW, a good hose clamp made of good stainless steel (unlike the most common stuff you may find out there), properly tightened and closely fitting the frame tube so it can't move or deform, is sufficient. If it can deform or shift around, it'll let the arm move around and probably damage the clamp and get worse over time. I've used older Ideal brand clamps salvaged from decades-old cars and such to secure all sorts of things very tightly, including my original CrazyBike2's frame, cargo rails, seat, etc., while I was experimenting with all that, and the only ones that failed were either the only clamp on a very long (feet) lever arm of frame tubing that could wiggle around (way more torque than a motor will put on one clamp), or ones that didn't tightly fit the things they were clamping (like clamping square tubes instead of round, or too small a tube for the clamp design, etc).

Same thing for using the same clamps to secure wrenches repurposed as torque arms on front fork hubmotors.


I have had plenty of broken cheap crappy clamps even when used correctly (since they weren't actually designed to do this job, it's not surprising). Some of the ones from Harbor Freight broke just tightening them down on actual hoses (garden hose repairs).

 

[99t4]

I like everything about the regen torque arm except one. Hose clamps that hold down the anchor point of the torque arm.

I'll reinforce what AW said-- A good quality hose clamp can quite sufficiently anchor the TA to the frame. The parts must be in good alignment, without any inherent "stress risers."