[Diy_efi] OT: torque question for the ME types

Allyn amalventano at sc.rr.com
Fri Apr 4 21:32:51 GMT 2003


M,

thanks for the info. i hadnt thought about the difference in k value. this
definitely shows that the stainless wont be good for this job.
do you by chance know of a good online supplier for zinc coated socket head
cap screws?
all that i have found seem to only stock standard, where my application uses
metric.
thanks
Al


----- Original Message -----
From: "Mr. Goat" <goat at notevil.net>
To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
Sent: Friday, April 04, 2003 2:17 AM
Subject: Re: [Diy_efi] OT: torque question for the ME types


> Before you go and throw those bolts in your rim a little bit of info on
your
> bolts...
>
> 12.9 is what is commonly referred to as a high tensile bolt. It has a
> ultimate tensile strength of 1200Mpa and it's yield stress is 960Mpa. 12.9
> bolts are tightened with a torque wrench right up to 90% of their ultimate
> tensile. There is no other effective way to tighten a 12.9 bolt. If nuts
are
> to be captured then Loctite, safety wire or nyloc's must be used.
>
> The stainless bolts are A2-70, I'm guess as that is the most common of the
> metric stainless bolts. Ultimate tensile is 700Mpa and yield is 450Mpa.
They
> are about 10% weaker then 8.8 bolts.
>
> The reason that your torque readings are higher on the stainless bolt is
> because A2 bolts have approximately twice the k-value of the corresponding
> steel fastener. This doesn't necessarily mean that stainless fasteners
> require double the specific torque since they usually cannot achieve the
> strength of a steel fastener.
>
> I can babble for pages as to why the manufacturer spec'ed 10.9+ grade
bolts,
> since the correct design of a bolted joint is quite involved. Fortunately,
> this isn't a machine design list so if you want my honest suggestion. Look
> for chrome plated or zinc plated 12.9 grade bolts. Two popular brands are
> "Unbrako" and "Holo-chrome".
>
> Cheers,
> M.
> ----- Original Message ----- >
>
> > - wheels are 17"x8" and 17"x11"
> > - bolts are M6x35mm, 1mm pitch, socket head cap screw (shcs)
> > - 35 bolts per wheel
> > - sections go together in such a way that there is no shear stress on
any
> > bolts (only tensile).
> > - original bolts found on wheels were class 12.9 (and rusting like
crazy)
> >
> > the manufaturer recommended at least grade 10.9, and to torque at ~12
> > ft-lbs, and no greater than 15 ft-lbs. their torque spec seems pretty
> > restrictive for a 10.9 bolt.
> >
> > my intention was to go with a stainless type of shcs, as any of the
> > 10.9/12.9 bolt grades tend to corrode much easier, and in my application
> the
> > screw heads are high visibility items. I purchased some 302 stainless
> bolts
> > of the same size as those removed. upon inspection, the new bolts were
> > stamped 'A2'. i did some destructive testing of these items, and was
able
> to
> > reach 15 ft-lbs with no yield. yielding began at ~18 ft-lbs, and torque
> > remained at ~19 ft-lbs for one full turn, at which point the bolt shears
> > near its center.
> >
> > my guess is that the manufaturer is failing way safe on the bolt grade.
> >
> > can the A2 (stainless) bolts be sufficient for this task?
> > perhaps the bolts i purchased are much stronger than they should be?
> > is there something that i am overlooking?
> >
> > thanks for any assistance
> > Al Malventano, ETC(SS), USN
>
>
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