Do you really need to torque a through axle?

[spokewrench]

No need. I have had thru-axles in my both e-bikes for several years, the first such an e-bike since Nov 1st 2019
Anyway: if any grease then on the thread only.

OTOH, maybe the threads are intended not to be greased so they would stick and not work loose.

 

[Stefan Mikes]

OTOH, maybe the threads are intended not to be greased so they would stick and not work loose.

Come on... with the torque of 12 Nm? This is a lot! I have removed and replaced wheels on my both e-bikes for numerous times. No worries.

 

[spokewrench]

Come on... with the torque of 12 Nm? This is a lot! I have removed and replaced wheels on my both e-bikes for numerous times. No worries.

Mine's the same way. I don't see anything but thread friction to keep it in place. The rear nuts are 45 Nm, and they're serrated.

 

[Stefan Mikes]

Mine's the same way. I don't see anything but thread friction to keep it in place.

Think of the thru-axle as of a bolt with a nut. Do bolts keep because of the friction in the thread?

The answer: Most bolts keep because they are torqued. There are some special threads that intentionally do not hold: for instance the cymbal stands (drums & percussion). The cymbal has to sway on the stand, so the thread is made the way the nut doesn't hold and moves up and down. Not the case for the regular threaded bolts and nuts.

The technical name for a regular thread is 'self-locking'.

 

[spokewrench]

Think of the thru-axle as of a bolt with a nut. Do bolts keep because of the friction in the thread?

The answer: Most bolts keep because they are torqued. There are some special threads that intentionally do not hold: for instance the cymbal stands (drums & percussion). The cymbal has to sway on the stand, so the thread is made the way the nut doesn't hold and moves up and down. Not the case for the regular threaded bolts and nuts.

The technical name for a regular thread is 'self-locking'.

If normal threads can be counted on to keep a bolt from turning, why use liquid thread lockers? Why are there so many washers and other mechanical devices to keep nuts from loosening? Why do some nuts use nylon inserts to prevent loosening? Thread friction is counted on to hold lug nuts on a car. To that end, manufacturers specify that the threads be clean and dry.

I grease my through axle, but I wonder if this could make the threads more likely to loosen.

 

[Stefan Mikes]

I'm sure the thru-axle thread is manufactured as a self-locking one (it is precision machining), and the axle diameter is rather big. Thread-locker is usually applied on very small screws that cannot be machined to a tight tolerance, are basically not to be removed, and which undergo vibration. A small screw can actually loosen itself. Threads hold because of the stress applied during the tightening. You cannot apply high torque on a small screw because you can pull it through.

Washers are usually applied to steel bolts/nuts to increase the surface on which the bolt can act, to prevent the surface from damage, help control corrosion, and make pull-through less probable.

I consulted the matter of greasing threads with my brother. He said: 'No grease whatsoever on a thread!' The only exception are connections made of different materials (alloy/steel) such as the pedal threaded into the crankarm. No grease but anti-seize paste there.

 

[spokewrench]

I'm sure the thru-axle thread is manufactured as a self-locking one (it is precision machining), and the axle diameter is rather big. Thread-locker is usually applied on very small screws that cannot be machined to a tight tolerance, are basically not to be removed, and which undergo vibration. A small screw can actually loosen itself. Threads hold because of the stress applied during the tightening. You cannot apply high torque on a small screw because you can pull it through.

Washers are usually applied to steel bolts/nuts to increase the surface on which the bolt can act, to prevent the surface from damage, help control corrosion, and make pull-through less probable.

I consulted the matter of greasing threads with my brother. He said: 'No grease whatsoever on a thread!' The only exception are connections made of different materials (alloy/steel) such as the pedal threaded into the crankarm. No grease but anti-seize paste there.

I torqued my BB shell to 35 Nm. I thought like you, so I couldn't account for it when it loosened. Park Tool recommends thread locker. Crank arm bolts are tightened with a lot more torque than thru-axles. The ones I've seen have come from the factory with thread locker.

it seems that grease could let a connection loosen, but I don't know if cases have been documented, such as lug nuts. If you torque to specs for clean threads, grease can cause you to produce more clamping force than intended. Measurements have proved that. (Maybe that's a reason to ignore the specs and tighten until you feel the clamping force take up the elasticity. )

 

[Stefan Mikes]

Thru-axles are designed to be removed and replaced often. Their design and function does not require a high torque.

BB is a rotating part while thru-axle is not.

 

[spokewrench]

Thru-axles are designed to be removed and replaced often. Their design and function does not require a high torque.

BB is a rotating part while thru-axle is not.

The shaft of the BB rotates. The body of the BB holds the ball bearings that allow the shaft to rotate freely. Well, if it really spun freely, you could clamp the end of the shaft in a vise so that it extended horizontally, and give the body a spin about the shaft. If it really spun freely, it would still be spinning a minute later. There's drag from the lube, but in Nm it must be tiny.

I tested the drag with a BB I'd replaced because the bearing drag had become abnormally high. I wrapped a string around the body ( radius 17mm ), tied it to a cup weighing 137g, and raised the horizontal BB by the shaft ends. When the string started to lift the cup, the BB turned. So the drag was less than .023 Nm.

I use a torque wrench on BB shells because the technology is a bit new to me. If ball bearing drag in the range of .02 Nm could turn a shell tightened to 35 Nm, I'd say the threads did not lock at all.

That seems to be why thru-axles don't come loose. Because they're inserted from the right, any torque transmitted through the wheel bearings would tend to hold them tight. I think torquing is not to keep them from unscrewing but to make the assembly rigid.

How about crank bolts? They don't seem to be exposed to any rotational force. They seem to require thread locker in spite of high torque specs.

 

[Stefan Mikes]

How about crank bolts? They don't seem to be exposed to any rotational force. They seem to require thread locker in spite of high torque specs.

What I have on my Specialized e-bikes is a design called "self-extracting crankarm". The crankarm is expected to be installed on the mid-motor spindle.

Please ignore the outer ring: it is what a normal user never even touches. There is an 8 mm hex socket in the centre of the crankarm nut. To remove, you insert the end of a 8 mm 4" long hex wrench into the socket and start rotating anti-clockwise (as for a regular bolt). After several turns, the crankarm is totally extracted from the motor spindle! To do the opposite action: Put the thread of the crankarm onto the motor spindle and start rotating the hex key clockwise. The work is a little bit hard as pulling the crankarm onto the spindle requires some force. Now, eventually you should use an automotive torque wrench and tighten to 50 Nm. However, it is enough to pull the end of the 4" hex wrench with the full hand force, and you will notice it is not possible to rotate the nut any more!

I'm fortunate to only own e-bikes with "self-extracting crankarms", which is in my opinion the most advanced technology in the market. I have forgotten how that was done on older bikes!

 

[m@Robertson]

<snip>

You're being silly. This is not a subject that takes a brain surgeon or a Youtuber to tell you what to think to realize the sensible play. btw I use Wera torque wrenches except for that little multifunction roadside kajigger. Total overkill but I use them regularly.

Again, most of the risk for the occasional mechanic is with over-torqueing because its far from obvious how low the stop value should be (@Chargeride gives a great example, and a seatpost clamp is another common fukup, as are the clamp at the saddle rails). But another standout are the crank bolts where the opposite (under-torqueing) is the common problem. So take the guesswork out so you are always close to where you need to be.

Its a crutch to long term learned expertise... sure, but the home bike mechanic has other things to do than obsess over this. And even if you know wtf you are doing, a torque wrench enforces easy-peasy consistency in your work. And it now seems painfully clear a big risk is you come across some crackpot (on the internet... go figure) who goes bonkers arguing over nothing.

 

[m@Robertson]

Ahh Crap !!
I thought that was a 7.
I had to put on my reading glasses and take another picture.

What I did was read the Nm which were easy to see, then googled "42 Nm to ft lbs". I couldn't tell if it was a 1 or a 7 either but I got the 4 and the 2 no problem.

 

[PCeBiker]

I just bought this,..

It's the tiny stuff that I always over torque.

When I screwed the covers back on my battery I over torqued them and all 8 little screws broke through the plastic on both ends of the battery.
I used Gorilla Tape and black RTV silicone to hold it shut and seal it.

 

[spokewrench]

What I have on my Specialized e-bikes is a design called "self-extracting crankarm". The crankarm is expected to be installed on the mid-motor spindle.



Please ignore the outer ring: it is what a normal user never even touches. There is an 8 mm hex socket in the centre of the crankarm nut. To remove, you insert the end of a 8 mm 4" long hex wrench into the socket and start rotating anti-clockwise (as for a regular bolt). After several turns, the crankarm is totally extracted from the motor spindle! To do the opposite action: Put the thread of the crankarm onto the motor spindle and start rotating the hex key clockwise. The work is a little bit hard as pulling the crankarm onto the spindle requires some force. Now, eventually you should use an automotive torque wrench and tighten to 50 Nm. However, it is enough to pull the end of the 4" hex wrench with the full hand force, and you will notice it is not possible to rotate the nut any more!

I'm fortunate to only own e-bikes with "self-extracting crankarms", which is in my opinion the most advanced technology in the market. I have forgotten how that was done on older bikes!

I believe the part you call the crankarm nut, I would call the crankarm bolt because I believe it has external threads. (To be old-fashioned, I'd call it a screw. Traditionally, a "bolt" was a screw if you tightened it by turning it. A bolt was designed to hold still while you turned a nut. The manufacturing specs were a little different.)

The outer ring traps the head of the crankarm bolt so it can extract the crankarm. There must be a lot of friction between the bolt head and the ring, but I guess it works. The advantage is that you don't need to screw an extractor into threads similar to those that hold the ring. (Those little devices are probably under $10.)

This year I had to replace a crankarm. If it had been self-extracting, I guess I would have had to locate one that matched, pay the price of proprietary hardware, and wait for it to arrive. With a more universal kind, I would have had an easier, quicker, cheaper problem. In fact, it cost me no money or delay because I had a suitable crankarm lying around.

I remember an older kind of crankarm locked on with a bolt having a wedge head. Unscrew the nut a couple of turns, break loose the wedge by tapping the nut, remove the nut and bolt, and the crank comes right off!

 

[BEC111]

@BEC111: I have found something quite interesting. I removed the front thru-axle from my Vado SL to take a picture this morning. Then I user my Pro Bike Tool torque wrench and tightened the axle at 12 Nm (which I think is a pretty correct figure). Then I decided to loosen and re-torque the real axle properly. Will you believe if I tell you that the axle, which I had previously tightened by the feeling had been over-torqued?

Nothing can replace a good torque wrench!

Your experiment demonstrates why I asked the original question. I am going to have to get a better wrench than the Lezyne.

 

[m@Robertson]

I consulted the matter of greasing threads with my brother. He said: 'No grease whatsoever on a thread!' The only exception are connections made of different materials (alloy/steel) such as the pedal threaded into the crankarm. No grease but anti-seize paste there.

If you google up Park Tool's crankarm installation video tutorial, you'll see the installation portion begins with "anti-seize or grease should always be applied to the threads of the bolt" as the first thing they say when describing the procedure. I've seen that done in bike shops, too. The video is tee'd up to where the Installation section begins, and includes the short-and-sweet explanation as to why.

Something I learned while doing wheel torqueing on cars on the race track: Everyone uses anti-seize on the wheel studs (steel studs and steel nuts). The reason for this is lubricated threads prevent thread galling, which is an issue on a high torque part that is going to get worked frequently. No other reason, in that particular application. Lubricated threads DO change the torque applied to the nut, since that nut can slide along the bolt more easily. The standard rule of thumb (and thats all it was, although it was based on collective experience and not idle conversation) was to back off whatever the factory spec was for a given set of wheel studs/nuts by 10%.

Interestingly, the Park tutorial assumes that greased threads are an integral part of the process and they do not recommend backing off.

 

[Stefan Mikes]

Ever installed a self-extracting crankarm?

 

[spokewrench]

Ever installed a self-extracting crankarm?

I tried, but it kept extracting itself!

 

[spokewrench]

If you google up Park Tool's crankarm installation video tutorial, you'll see the installation portion begins with "anti-seize or grease should always be applied to the threads of the bolt" as the first thing they say when describing the procedure. I've seen that done in bike shops, too. The video is tee'd up to where the Installation section begins, and includes the short-and-sweet explanation as to why.

Bolts for BSA cranksets come with threadlock. Grease would defeat the purpose.

The video said manufacturer specs vary from 30 to 45 Nm. Aventon has published a sheet of 52 torques for the Abound. Several are for the birds. They say 40-45 Nm for crank bolts.

The bolts are 5/16 -24, often labeled as M8 x 1.0. The maximum recommended torque for an 8.8 grade M8 x 1.25 is 25 Nm. With a finer thread, a 5/16 -24 would have a limit lower than 25 Nm. I believe I know why Aventon's spec is so much higher. For legal reasons, dealers would want published specs. I've read that the company's American staff is tiny. I believe somebody with a torque wrench measured what it took to break loose connectors on bikes from Shanghai. Depending on the alloys involved, it can take a lot more to snap a bolt loose than it took to tighten it several months earlier.

Around 1955, I discovered that standard combination wrenches are sized so you can't comfortably apply more torque than is generally safe; for exceptions, you can pad the handle with a rag or tap it with a hammer. It took me till 1970 to realize a standard allen key set is sized the same way. I can't rely on published specs. To help prevent overtorquing, I bought a standard set of allen keys. It came with a yellow plastic handle for times when I need more torque.

In the photo, I've set up a strain gauge to see what torque I got on the H8. Barehanded, I could apply 110 Newtons through the bolt to the pedal 17 cm away, or 19 Nm. I put the handle on and found that I could comfortably push much harder. The bolt budged at 160 N on the gauge. I stopped because it felt tight enough. That was 27 Nm. If I'd known more about the bolt, I wouldn't have used the handle. If I'd known the bolt was SAE, I would have used the 5/16 allen key. It would have given me about 21 Nm barehanded, which probably agrees closely with the recommended max for that bolt.

 

[m@Robertson]

A professional installation of crankarms includes anti-seize. The reason is simple to understand. The Park series of bicycle maintenance tutorials are the gold standard for professional-level instruction. Do they stand alone in this or is it something that is more or less common knowledge among people who do this sort of thing? I went to Youtube and searched for 'bicycle crankarm installation' and ran down the list.

Not the industry leader; just a neighborhood fixit guy from the looks of it. And he knows this basic step (vid is tee'd up).

And another...

And still another. This guy is all visuals but you can see within the first 10 seconds (and a minute in for the other side) how he greases the bolt.

I could go on but thats plenty of time to waste on this only-on-the-internet kind of argument.