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Old September 12th 07, 10:25 PM posted to rec.autos.tech,rec.autos.rod-n-custom
N8N
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Default How are bolt torque specs arrived at?

On Sep 12, 5:13 pm, (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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