Bluemoon
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| posted on 23/6/06 at 02:41 PM |
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Bolt problems..
Hi all,
Torqued up some 8.8 grade M8 bolts (Zinc plated). Looked up the required torque as 30 NM. Bolt's streched before this, what am I doing worng?
I think these bolts marked incorectly!! Anyone else come across this?
Cheers
Dan
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David Jenkins
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| posted on 23/6/06 at 02:53 PM |
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There are a lot of counterfeit bolts out there - it's very scary when you think about it. Even worse, there's a high level of
counterfeiting in aircraft components! Now that's REALLY scary...
All you can do is buy brand names from a reputable source, and then hope.
As a matter of interest, are you SURE that your torque wrench is reasonably correct? 
David
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ned
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| posted on 23/6/06 at 02:57 PM |
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torque wrenches should be left unwound or the spring can get pretensioned or stretch and give an inaccurate reading...
Ned.
beware, I've got yellow skin
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MikeR
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| posted on 23/6/06 at 03:02 PM |
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even at 20% out 30nm is sod all, a grade 8.8 should easily withstand a lot more than that.
(i have no idea what i'm talking about just my own personal, non scientific view)
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David Jenkins
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| posted on 23/6/06 at 03:09 PM |
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Roughly 22 ft/lb, according to my converter program.
That's quite a lot for a M8 bolt if it's not high-tensile.
David
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iank
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| posted on 23/6/06 at 03:15 PM |
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30Nm is too much for an 8.8 M8 according to this ref:
http://www.nord-lock.com/default.asp?url=338.16.37
and here
www.norbar.com/content/cms/TorqueValueGuide.pdf
[Edited on 23/6/06 by iank]
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Bluemoon
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| posted on 23/6/06 at 03:34 PM |
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Iank, I think it's just correct, as it was a zinc plated bolt and nut so a 1.2 multiplyer of 25.5Nm is 30.6Nm...
Also checked torque wrench with scales, needs 7kg at 43cm, wich I recon is 30Nm.
Tried to diffrent bolts from the same supplyer same thing happed.. Did'nt get anywere near 30NM before it felt odd...
Dan
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Marcus
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| posted on 23/6/06 at 03:46 PM |
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quote:
Did'nt get anywere near 30NM before it felt odd...
You're not torquing into Aluminium are you? Could be close to stripping threads rather than stretching bolts!
Marcus
Because kits are for girls!!
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iank
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| posted on 23/6/06 at 03:46 PM |
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Not an expert by any means, but that first link claims 24.5 Nm for zinc plated 8.8 M8 assembled dry.
But I agree that is recommended torque not torque to kill the thing, there should be a heafty safety margin built into those figures. If it stretched
much earlier than 30 then something is clearly wrong!
Might be worth calling Namrick (http://www.namrick.co.uk) or someone else reputable to get their opinion, and order some decent ones.
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donut
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| posted on 23/6/06 at 04:07 PM |
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what are you bolting?
Andy
When I die, I want to go peacefully like my Grandfather did, in his sleep -- not screaming, like the passengers in his car.
http://www.flickr.com/photos/andywest1/
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Danozeman
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| posted on 23/6/06 at 04:58 PM |
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quote:
You're not torquing into Aluminium are you? Could be close to stripping threads rather than stretching bolts!
That can happen in steel aswell. If the threads are old and likeyl to have been done up and undone lots of times this could easily happen. The pitch
on an M8 isnt that deep.
Dan
Built the purple peril!! Let the modifications begin!!
http://www.eastangliankitcars.co.uk
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Bluemoon
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| posted on 23/6/06 at 05:06 PM |
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o.k;
Not bolting Ali.
Nut and bolt both BZP, 8.8 M8. Nut is a nyloc, both new from supplyer.
It's for the handbrake lever (don't realy need this much torque I guess), but that's not the point, it makes all the other
nut's and bolts suspect I have from this supplyer.
It's a good job I know where all these nuts and bolts are at the moment
(two are holding the Master cylinder on).
[Edited on 23/6/06 by Bluemoon]
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gustavo_brum
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| posted on 24/6/06 at 03:53 AM |
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30Nm isn much, really, but you really don need it for a handbrake lever. However, if you want to be sure, swich to allen bolts, which are grade 12.9
and there is no way to miss.
just a suggestion...
by the way, zinc plating (as any electrolytic treatment) causes stress risers, so they are usually not as strong as non-plated ones)
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