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#1
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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/ -- underground experts united http://user.it.uu.se/~embe8573 |
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#2
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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/ -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#3
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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. |
#5
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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
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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
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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
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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 -- underground experts united http://user.it.uu.se/~embe8573 |
#9
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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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