How are bolt torque specs arrived at?

On Sep 11, 10:50 pm, Doc wrote:
> Just pondering the 9 ft/lbs specified for the rear seal housing on my
> Cressida per the factory manual. How are bolt torque numbers
> determined?

They are determined by "tensile strength"

Here's an interesting link for ya:
http://www.raskcycle.com/techtip/webdoc14.html
 >> Stay informed about: How are bolt torque specs arrived at? 

Comboverfish wrote:
> On Sep 11, 9:50 pm, Doc wrote:
>> Just pondering the 9 ft/lbs specified for the rear seal housing on my
>> Cressida per the factory manual. How are bolt torque numbers
>> determined?
>
> Basically it is a specification that has been determined by past
> testing and documentation of the given fastener type plus engineering
> consideration of the assembly parts in question. The two most
> important things regarding the fastener are 1) it must not break/strip
> threads at this torque value and 2) it must not back out from lack of
> tension. The makeup of the parts and their intended duty modify this
> equation as well.
>
> In the case of a final assembly, lots of data is reviewed before
> assigning a value to a fastener. Machining and material spec data
> publications are used by design engineers as a baseline towards
> engineering their specific requirements.
>
> Toyota MDT in MO
>

The most important thing is that the fastener is preloaded more than the
load it will see.
 >> Stay informed about: How are bolt torque specs arrived at? 

dahpater wrote in
@o80g2000hse.googlegroups.com:

> On Sep 11, 10:50 pm, Doc wrote:
>> Just pondering the 9 ft/lbs specified for the rear seal housing on my
>> Cressida per the factory manual. How are bolt torque numbers
>> determined?
>
> They are determined by "tensile strength"
>
> Here's an interesting link for ya:
> http://www.raskcycle.com/techtip/webdoc14.html
>
>


Another good one:
http://www.boltscience.com/

--
Tegger
 >> Stay informed about: How are bolt torque specs arrived at? 

"Doc" wrote in message

> Just pondering the 9 ft/lbs specified for the rear seal housing on
> my
> Cressida per the factory manual. How are bolt torque numbers
> determined?

This is a very complicated issue. In general the engineers would
determine a target clamping force and work backwards from there to
determine a tightening torque. For a gasketed joint, they would
determine a bolt pattern and pick a bolt size to provide the required
clamping force (and consider the mechanical strength for a load
carrying member). The bolts would be sized so that when properly
torqued they would be at something like 80% of their proof load. The
torque needed to achieve this clamping force is a function of the
materials involved (bolt material and base material for female
threads), plating (these affect the frictional characteristics of the
joint as the bolt is torqued), lubrication (another contributor to
frictional characteristics), head style, etc. The type of loads the
bolt would be subjected to would also be important (axial, shear,
combination, static, varying, etc.) For a joints subjected to varying
axial loads, they would go for a higher percentage of the proof load
(90 to 100%). Most modern head, rod, and main bearing cap bolts are
torqued to the yield point. This is done using specialized machines
that sense a change in the stress strain relationship as the bolt
reaches the yield point. This is a very good way to torque bolts for
variable loads, but difficult to duplicate in a repair environment.

I have some information of torque settings at
http://home.mindspring.com/~ed_white/id9.html , but it is simple
information related to steel on steel joints with non-reversed
stresses.

Ed
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On Sep 12, 1:54 pm, "hls" wrote:
> "C. E. White" wrote in message This is done
> using specialized machines
>
> > that sense a change in the stress strain relationship as the bolt reaches
> > the yield point. This is a very good way to torque bolts for variable
> > loads, but difficult to duplicate in a repair environment.
>
> I have seen bolt elongation gauges advertised and recommended for
> performance
> engine building. They are not so expensive.
>
> I have never used one of them, and wonder if anyone here has any comments on
> them.

If you know the elastic modulus of the bolt that you are tightening,
it is theoretically MUCH more accurate than torque and completely
takes thread and nut/surface interface friction out of the picture.
However, I have not used one either.

nate
 >> Stay informed about: How are bolt torque specs arrived at? 

"C. E. White" wrote in message This is done
using specialized machines
> that sense a change in the stress strain relationship as the bolt reaches
> the yield point. This is a very good way to torque bolts for variable
> loads, but difficult to duplicate in a repair environment.


I have seen bolt elongation gauges advertised and recommended for
performance
engine building. They are not so expensive.

I have never used one of them, and wonder if anyone here has any comments on
them.
 >> Stay informed about: How are bolt torque specs arrived at? 

On Sep 12, 5:13 pm, klu... RemoveThis @panix.com (Scott Dorsey) wrote:
> hls wrote:
> >"C. E. White" wrote in message This is done
> >using specialized machines
> >> that sense a change in the stress strain relationship as the bolt reaches
> >> the yield point. This is a very good way to torque bolts for variable
> >> loads, but difficult to duplicate in a repair environment.
>
> >I have seen bolt elongation gauges advertised and recommended for
> >performance
> >engine building. They are not so expensive.
>
> >I have never used one of them, and wonder if anyone here has any comments on
> >them.
>
> We use them on airplanes. They are much more accurate than torque gauges
> because they don't rely on thread friction.
>
> They would seem overkill for auto applications, but more importantly they
> would seem useless because the numbers in the engine manuals are all torque
> specs rather than elongation specs. So you'd have to develop your own
> nominal values for reference, which is probably fine for a one-off engine
> that is being constantly rebuilt but otherwise impractical.
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

I think that is where they are most often used, in race or race/street
engines where the stock specs don't even apply anymore. I think that
ARP will give you stretch specs for their fasteners if you ask.

nate
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hls wrote:
>"C. E. White" wrote in message This is done
>using specialized machines
>> that sense a change in the stress strain relationship as the bolt reaches
>> the yield point. This is a very good way to torque bolts for variable
>> loads, but difficult to duplicate in a repair environment.
>
>I have seen bolt elongation gauges advertised and recommended for
>performance
>engine building. They are not so expensive.
>
>I have never used one of them, and wonder if anyone here has any comments on
>them.

We use them on airplanes. They are much more accurate than torque gauges
because they don't rely on thread friction.

They would seem overkill for auto applications, but more importantly they
would seem useless because the numbers in the engine manuals are all torque
specs rather than elongation specs. So you'd have to develop your own
nominal values for reference, which is probably fine for a one-off engine
that is being constantly rebuilt but otherwise impractical.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
 >> Stay informed about: How are bolt torque specs arrived at? 

hls wrote:
>
> "C. E. White" wrote in message This is
> done using specialized machines
>> that sense a change in the stress strain relationship as the bolt
>> reaches the yield point. This is a very good way to torque bolts for
>> variable loads, but difficult to duplicate in a repair environment.
>
>
> I have seen bolt elongation gauges advertised and recommended for
> performance
> engine building. They are not so expensive.
>
> I have never used one of them, and wonder if anyone here has any
> comments on
> them.

I've use them on sbc rod bolts. Arp gives a couple of torque values
(depending on the lube used) and a stretch value.
 >> Stay informed about: How are bolt torque specs arrived at?