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allen screws and torque



 
 
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  #1  
Old October 21st 18, 08:02 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 1,035
Default allen screws and torque

I take it allen screws (or "socket head cap
screws") and hex bolts have the same standard
torque values?

If I read the charts [1] correctly, if you find
an allen screw on your bike that takes a 4mm
allen key, then its an M5, and assuming "clean,
dry threads" with 8.8 "relative strength
marking", the maximum torque is 6Nm?

I rode my bike some 40km yesterday, and noticed
a couple of things. One was that the left
shifter and hand brake was just a bit (~1mm)
too high, while the right one, while at the
same level, was just right.

Later, I was done fixing that, I checked with
the torque wrench, and both screws fell just
a little short of the prescribed 6 and 10Nm for
M5 and M6, respectively.

[1] http://user.it.uu.se/~embe8573/allen-torque/

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  #2  
Old October 22nd 18, 03:59 AM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 2,908
Default allen screws and torque

On Sun, 21 Oct 2018 21:02:44 +0200, Emanuel Berg
wrote:

I take it allen screws (or "socket head cap
screws") and hex bolts have the same standard
torque values?


Sorta. The maximum torque is normally a function of the threads and
material(s). However, for smaller hex head bolts, the head can be
broken off before the threads are stripped. I wouldn't worry about
that too much because for allen head cap screws, the head is stronger
than the threads and for the sizes normally found on a bicycle, the
hex bolt heads are also stronger than the theads.

However, the maximum torque is for the bolt, not the material the bolt
is threaded into. For example, if you were to torque a bolt to the
maximum torque allowed, in an aluminum block, it would strip the
threads out of the aluminum long before the bolt threads fail
(depending on how many threads are in the aluminum block). Look up
the recommended bolt torque in the brake and shifter data sheet.

"How much Torque does it take to Break a Bicycle Bolt?"
https://www.youtube.com/watch?v=vPFtEj4JZvA (7:36)

What maximum torque means is how much torque can be applied before the
threads strip. What recommended torque means is how much torque can
be applied for 0.2% bolt elongation.

If I read the charts [1] correctly, if you find
an allen screw on your bike that takes a 4mm
allen key, then its an M5, and assuming "clean,
dry threads" with 8.8 "relative strength
marking", the maximum torque is 6Nm?


Ummm... try this instead:
https://www.amesweb.info/Screws/Metric_Bolt_Grades_Strength.aspx
A 5mm type 8.8 bolt is rated at 7.6Nm maximum breaking torque. That
means exactly what it says. Torque it to 7.6Nm and it will break.

I rode my bike some 40km yesterday, and noticed
a couple of things. One was that the left
shifter and hand brake was just a bit (~1mm)
too high, while the right one, while at the
same level, was just right.

Later, I was done fixing that, I checked with
the torque wrench, and both screws fell just
a little short of the prescribed 6 and 10Nm for
M5 and M6, respectively.


Offhand, if the bolt was loose AFTER applying maximum torque, you've
probably stripped the aluminum threads in the brake and shifter body.

Hint: Stay away from the maximum torque.

[1] http://user.it.uu.se/~embe8573/allen-torque/

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150 Felker St #D
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Skype: JeffLiebermann AE6KS 831-336-2558
  #3  
Old October 22nd 18, 04:40 AM posted to rec.bicycles.tech
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Default allen screws and torque

Offhand, if the bolt was loose AFTER applying maximum torque, you've
probably stripped the aluminum threads in the brake and shifter body.

Hint: Stay away from the maximum torque.


Yeah, I thought so too. After doing them the maximum torque But they aren't loose! And it isn't threads into the aluminium frame. It is a clamp. This isn't to say it couldn't have been damaged just as well.

  #4  
Old October 22nd 18, 04:53 AM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 2,908
Default allen screws and torque

On Sun, 21 Oct 2018 20:40:02 -0700 (PDT), wrote:

Offhand, if the bolt was loose AFTER applying maximum torque, you've
probably stripped the aluminum threads in the brake and shifter body.

Hint: Stay away from the maximum torque.


Yeah, I thought so too. After doing them the maximum torque
But they aren't loose! And it isn't threads into the aluminium frame.
It is a clamp. This isn't to say it couldn't have been damaged just as well.


Steel nut or aluminum nut?

Take it apart and look at the threads. Any damage? Any teeth
missing?

Is the bolt a tight fit into the nut (without the brake body to get in
the way), or is it flopping around loosely?

Did you grease, lube, anti-seize, or Teflon tape the threads? That
will decrease the maximum torque.

Anything unusual on the handlebars, such as clamping the brake levers
over bar tape or gum brake covers?

Any tears or cracks in the stainless(?) steel strap where it mates
with the break body bolt?

A 10x binocular microscope really helps with mechanical inspections:
http://www.learnbydestroying.com/jeffl/pics/microscopes/Olympus%20SZ30/slides/SZ30-01.html

--
Jeff Liebermann

150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #5  
Old October 22nd 18, 05:09 AM posted to rec.bicycles.tech
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Posts: 11
Default allen screws and torque

Steel nut or aluminum nut?

For some reason I assumed an 8.8 stainless steel nut, that's where I got the 6 and 10Nm for M5 and M6, respectively, but I don't know. It is Shimano SLX 2*11 shifters. I don't know the material of the clamps. Perhaps I can find a manual on the net.

Is the bolt a tight fit into the nut (without the brake body to get in
the way), or is it flopping around loosely?


No, everything looks and works great!

Did you grease, lube, anti-seize, or Teflon tape the threads? That
will decrease the maximum torque.


Yes I know, see the OP. So no, no grease.

The thing I wonder at the moment, assuming I got lucky and there is no damage, should I still loosen it up? What will happen if I run into a tree? Will the high torque or the low(er) torque be better then for the bike?

BTW on the handlebars are a couple (6?) of M5s. There they say explicitly max 6Nm. Which is the max for M5s. I tried all of them with my torque wrench set at 6 and they were all at 6 or higher already!
  #6  
Old October 22nd 18, 06:19 AM posted to rec.bicycles.tech
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Posts: 11
Default allen screws and torque

The shifter (SL-M7000) should be 3-4Nm! [1] Gulp!

The brake should be 6-8, however they do that with an M5, exceeding the previously mentioned max! Maybe some other material? I have an M6 there, so it isn't the same model. I have a BL-425 - I found a manual [2], but it focuses on the disc brake, not the lever.

Because they do 6-8 with and M5, perhaps 10 with an M6 is OK even tho it is the maximum.

[1] http://si.shimano.com/pdfs/dm/DM-MBSL001-01-ENG.pdf
[2] http://si.shimano.com/pdfs/dm/DM-BR0005-13-ENG.pdf
  #7  
Old October 22nd 18, 07:32 AM posted to rec.bicycles.tech
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Default allen screws and torque

OK, so I examined one of the M5s and it looked fine. However it was greased! I don't know why but I assumed they weren't. Loots of incorrect assumptions here, it seems.

While the screw itself looked fine, there were some blackish to the grease, could be whatever, but possibly indicating a damage to the clamp, if that is made of softer stuff than the bolt. But it isn't, right, because that would be dangerous in exactly this kind of situation! (Guy thinks he puts the bolt in, actually sticks it into a hole!)

Anyway I set them to the correct 4Nm.

The M6, to hold the brake levers, I put down to 9, not having an official reading what it should be.

BTW I discovered something with the M6s. A problem is the screw head is touching the thumb, it is too close to the shifter, and it is cold. But there is plenty of room on the other side! Only a little more difficult to operate. The angle is downward but not that much and it is such a long distance comparatively. Perhaps I'll change that next!

  #8  
Old October 22nd 18, 04:32 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 1,035
Default allen screws and torque

The M6, to hold the brake levers, I put down
to 9, not having an official reading what it
should be.


Still no luck finding the exact manual for the
BL-M425, but I found one for BL-M445 [1].
There, the correct torque is 6-8Nm. It also has
M6s so it is probably the same. Because I first
put it to 10, that's a 25% over torque at best,
so it'll be interesting to see what happens.

[1] http://si.shimano.com/pdfs/si/SI-8J50A-002-ENG.pdf

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  #9  
Old October 22nd 18, 08:26 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 1,035
Default allen screws and torque

OK, so I put the M6s to 8Nm. Now everything is
by the book save for ~invisible damage that
probably didn't happen to any great extent.

I was very tempted to try to seal the lever
from the other side - which I think would have
worked - but then I thought, for the moment
maybe I had already pushed my luck with bolts.

Instead, I think I'll just cut a small plastic
tube and push that over the bolt head to get
some insulation that way!

Ha! This much fun I haven't had in ages!
If I destroy any of these two bikes, I'll never
be able to afford any single one of them fair
and square. So it is exciting!

Once I knew I guy, blue collar guy, who bought
a very fine boat. Everyone was stunned by it.
I asked if he used it to go fish but he said he
didn't want the blood and stuff from the pikes
etc to mess it up. I'm pleased this whole
episode shows I'm not like him! In this respect
I mean, other than that he was/is a good
bloke...

--
underground experts united
http://user.it.uu.se/~embe8573
 




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