How much torque on the rear nuts?

[TMaster]

I have an aluminum frame, with the slotted rear triangle so the axle can't spin if the nuts were loose and can't slide either. How many Ft-lb's or Newton meters of torque should I put on the two large nuts for the 9C motor? The bike used to have the hand tighten quick release.

 

[dogman dan]

Tricky question to answer. Tight for sure, but not till it strips out the axle.. When I stripped an aotema motor, I was using all my strength on a long handle wrench. 30 years of construction, I can push pretty hard on something. Now I go pretty dang hard on the wrench, but only use a 6" crescent so I don't rip it to shreds. I can only guess how hard, not using a tourqe wrench. But much more than 10 ft pounds, and much less than 100...

See the fork donations threads last few pages for some real data on stripping threads, forces etc. It's a bit over my head.

 

[TMaster]

I put 25 or so Ft-lb's on the nuts, A little more then tightening the oil drain nut on your car I'll check it after a while. I looked up the spec for the normal quick release and it is about 6 ft-lb's so thats a bit more.

I scanned over the fork donation testing thread, and it seems like the issues are front forks, problems with the sizes of the axle flat spots smaller then the ID of the flat spots on the forks or rear. Weak Metal for putting on these honkin motors.

I took the nut off and took a couple pics, I don't think I will have any issues, but I could aways make a torque arm and mount it to the disc brake mount holes I suppose.

 

[dogman dan]

Nice flat dropouts, so no issues with the dang QR cup, and washers too big, so I'd just tighten it up good but not to the point of pushing hard on a long wrench.

Spinout is not any less likely on a rear install, so tight nuts are still needed. I wouldn't worry about crushing the frame aluminum with nut torque with a nice flat surface like that. And the good fit will ensure that they don't go and loosen on you later.

But a tourqe arm definitely will help. If anything is learned by Justins fork tests, it seems to me to be that torque of the nuts makes a huge difference in resisting spinout, and that a torque arm definitely helps even if the nuts get loose. Nothing wrong with belt and suspenders.

 

[TMaster]

Ok Thanks, What about the inside cylinder spacers? You think it may be wise to machine those down and put a large surface area of a thin steel washer in between? Maybe I'm just being too picky. haha

 

[dogman dan]

Not at all, a thin inner washer is a good idea. You may be able to simply spread the forks another few mm to fit two in.

 

[TMaster]

So I've had about 6 or 7 rides now and I pulled the nuts off to do some some maintenance and maybe replace my phase wires, and I noticed there now is a tiny bit of play around the axle in the slots It feels like the axle can rotate 2 or 3 degrees now. So, I either the 30 Ft-lb's wasnt tight enough or I'm going to have to make some torque arms that are totally exact with no play around the axle. I have a small CNC machine and I can make some aluminum ones, but steel is really tough to machine with what I have, takes 2 or 3 times as long.

I may have been ok in the beginning if I had put like 60 Ft lbs on the nuts instead, but too late now I think. Should I make the custom arms or just try and tighten the crap out of the nuts? I have some 1/4" 6061 aluminum. I would need to order steel if that is better, what thickness? Let me know what you guys think.

 

[amberwolf]

I don't know for sure, but I suspect the aluminum will just deform, even if it doesn't crack. You'd probably have to harden it after machining, via heat treating it, but I'm barely even an amateur at that sort of thing so take my advice with a salt lick or two.

For now you could just use wrenches.

 

[dogman dan]

Tighten too much, and you will strip your axle. But 25 ft pounds may not be enough. In a way, relying on torque arms only, and letting the dropout be oversize may be the best bet for aluminum dropouts. It won't crack if the axle doesn't lever on it. Good torque arms will limit motion enough with tight nuts.

 

[TMaster]

OK, I think I will make some custom arms for both sides. I have plenty of axle length on both sides for up to almost 1/2" of torque arm thickness even with the nut on all the threads. I want this bad boy to never fail! I got some ideas up my sleeves. The nuts are 14mm x 1.5 fine thread? I think I will order some nylon insert lock nuts. I found some grade 8's that should do.

 

[StevenR]

Check out the fork spin-out thread at...
http://endless-sphere.com/forums/viewtopic.php?f=2&t=14195
If that thread doesn't answer any question you have ever had on this topic, send him your frame for destructive testing...

 

[Jeevis]

I've killed 4 different forks with my front 2806. No amount of torque would save them....to the point me and the guys at the local shop had a difficult time getting them off to put on a new fork. One torque arm isn't enough, seeing as its broken the hose clamp right off. I know employ 4 torque arms two e-bike.ca front arms, a universal torque arm, a good ol 13 mm wrench which is probably the most effective of them all. In all honesty I'd say use as much torque as you can get with your arms. The 9c axles seem to be rather tough compared to others.

 

[TMaster]

Wow.... How much space do you have from the outside of fork slot to the inside of the nut?

 

[Bikemad]

I have an aluminum frame, with the slotted rear triangle so the axle can't spin if the nuts were loose.

I wouldn't be so sure about that.

I did some rough calculations on my motor and worked out that the force from the axle trying to spread the gap would be at least 500Kg (1100lbs)!
(That was with a measured force of just 15Kg (33lbs) at the tyre.)

Rear drop-outs are more vulnerable to damage from regen than power, as under regen the force is applied further from the weakest point allowing greater leverage to act upon the lower lug, which can eventually splay or break the dropout allowing the axle to spin or break away completely.

You need to realise that these drop-outs are not designed to take any torsional load with a standard axle because there is none, as the wheel is attached to the axle by bearings, which obviously cannot transmit any turning forces

I'm sure you'll agree there is an enormous difference between zero force and 500Kg of force trying to spread the drop-out.

With a 26" wheel, It's like putting a 13" long lever into the axle slot and applying force at the very end until something eventually gives.

In fact, the more I think about it, the more concerned I become!

Alan

 

[TMaster]

Yeah, I'm working on these right now. If it doesn't hold then steel it is! using 10-32 316SS screws with about 5/8" deep thread in the mount. Could go up to a M6 if i have too.

 

[John in CR]

I've killed 4 different forks with my front 2806. No amount of torque would save them....to the point me and the guys at the local shop had a difficult time getting them off to put on a new fork. One torque arm isn't enough, seeing as its broken the hose clamp right off. I know employ 4 torque arms two e-bike.ca front arms, a universal torque arm, a good ol 13 mm wrench which is probably the most effective of them all. In all honesty I'd say use as much torque as you can get with your arms. The 9c axles seem to be rather tough compared to others.

Jeevis are any of those forks good quality suspension forks? If so, maybe we can do a deal where I put you back in business with any of them that will be safe and secure, no torque arms needed, and axle nuts wouldn't even be mandatory. I want a quality fork out of the deal that is otherwise useless anyway due to the broken dropout.

 

[TMaster]

OK I finally finished my Torque arms! One is aluminum the other is 1018 steel. I clear coated the steel one. I ran out of material so had to make due with what I had. I had to make the design a litle different for the right side because of the room issues with the rear derailleur. I hope these hold! I marked some red lines accross the nut/washer/arm afterwards so I can see if anything moves. I upgraded to stainless steel axle spacers and stainless steel perfecting fitting washers on each side.

 

[Lyen]

OK I finally finished my Torque arms! One is aluminum the other is 1018 steel. I clear coated the steel one. I ran out of material so had to make due with what I had. I had to make the design a litle different for the right side because of the room issues with the rear derailleur. I hope these hold! I marked some red lines accross the nut/washer/arm afterwards so I can see if anything moves. I upgraded to stainless steel axle spacers and stainless steel perfecting fitting washers on each side.

Very nice fabrication stuff you have! You need to fabrication another TMaster and called it T2.

 

[TMaster]

lol, thanks, You need anything made let me know