Convert Degrees to Foot Pounds?

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Working on a Deutz Diesel engine. The instructions say to torque the bolts to 30 foot pounds then turn 45 degrees.

Can I convert the degrees to foot pounds so I can use a torque wrench to make them more exact?

Is there an abbreviation for "foot pounds"?

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Do what it says. There are factors that affect torque readings. The engineers have it right, no sense second guessing them.

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Yep. It is probably easier to turn 45 degrees and stop rather than to "torque" to some specified final amount.

Bob Swinney

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    No -- that would be making them *less* exact.

    Do you have an old school protractor? (The D-shaped thing with angles marked on it in degrees.) Use your torque wrench as instructed to tighten to 30 foot pounds, and then place the protractor to measure the angle of the wrench handle. Turn it an extra 45 degrees (1/8 of a full turn). This part is to stretch the bolt after you get it to that torque starting point. And that bolt should *never* be re-used -- you stretch it once, no more.

    "Ft-Lbs" is one.

    Enjoy,         DoN.

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wrote:

Doesn't every bolt stretch when you torque it down? How are these fundamentally different?

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wrote:

Also... Doesn't this assume that these bolts are tightened past their elastic limit? Past their UTS?

Surely not...

=Jeff R.

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Brain fart. I meant "Yield Stress"

(oops)

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wrote in message news:41a88252$0$17543

The tightening technique is to get the bolt very near the yield point, and not over it. However, if you reuse the bolt, you will exceed the yeld point. This will result in insufficient clamping pressure for the joint, and could (very likely, actually) result in broken fastners.

The torque technique is becoming industry standard nowadays, and that is because it is inherintly more accurate. If you torque a bolt to 70-80 lb-ft, the inaccuracies of the measurement grow expotentially as you increase torque due to friction, head galling, lubrication distribution and other variables during the tightening. By keeping the measured torque lower, you reduce these inaccuracies substantially. By specifying the angle of final placement from a lower given torque, you use the thread pitch to determine the linear stretch amount for the fastener.

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Anthony

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vaguely proposed a theory ......and in reply I say!:

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AFAICS, you shouldn't exceed the yield point if you use the bolt again. The whole idea of Yield point (and I am prepared to learn another lack in my "knowledge base here, believe me" is that it's the point at which the steel deforms permanently. Any bolt tightened to below the yield will return to its former length. (???)

I can see two possible problems. Metal fatigue if the bolt is in place for an extended time, and / oe under heat/cold/ vibration etc. Accidental overtightening. Thsi would be an enginerring tning. If the bolts were _really_ taken to near yield, there would little margin for error. But once a bolt has exceeded yield, it starts to lose tension anyway. That woud be dangerous.

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Old Nick wrote:

Ideally, this is true. i.e. Yield point is stress level that separates elastic (returns to original dimention when the stress is relieved) from plastic (returns to original dimention when the stress is relieved) deformation. Regretably most materials do not behave ideally so you will often see yield point defined as the point where residual deformation is some small percentage of original dimension.

Ted

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On Sun, 28 Nov 2004 20:03:17 GMT, Ted Edwards

......and in reply I say!:

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I am sorry. I am a bit confused by the above lines.

Which is to say that you use a bolt that only _just_ doesn't really do the job. <G>

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The concept behind stress to yield bolts is to get a very consistent bolt to bolt torque value when tightened according to the listed procedure. Many modern head bolts have a reduced diameter section on the shank for this purpose. Torque variance can be as small as 1% using this method. Ordinary torque wrench methods give a bolt to bolt consistency variance that is often as large as 20%. Consistent torque reduces the tendency of aluminum heads to warp.

Gary

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vaguely proposed a theory ......and in reply I say!:

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AFACUI, the answer is still no if you are asking about stretching. A spring is the most dramatic example of a metal that can be "stretched" without exceeding yield stress. To stretch steel you need to apply stress. It will start to stretch under very small stress. It will _permanently_ stretch when it passes yield.

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Jeff R. wrote:

The Eleventh Commandant: THOU SHALT NOT ASSUME! Regards. Ken.

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DoN. Nichols wrote:

Precisely!! Ken.

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On 26 Nov 2004 21:54:28 -0500, snipped-for-privacy@d-and-d.com (DoN. Nichols) vaguely proposed a theory ......and in reply I say!:

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Ok. Why should yopu not re-use the bolt? You are only stretching it, but not to Yield.

I have questioned Anthony about this. My theory says I am right, but you guys know your stuff. So fact is against me. I am never willing to let being thought a fool stop me from opening my mouth. I have leraned a lot that way...

...everything except when to keep my mouth shut! <G>

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Metal fatigue plays a factor once the bolt is stretched. I know that there are a number of engines that use this method in tightening head bolts. And they are not to be re-used under any circumstances.

Lane

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I think it's because they get hot while under tension and while getting hammered by the engine. That gives 'em a small amount of work hardening that won't like a restretch later on. I read it somewhere on the internet, but then again, I read it somewhere on the internet.

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Recently I borrowed some material from a friend on bolts and read a lot of it. And as usual the answer is " it depends ". Torqueing to a low value and then tightning a number of degrees was stated as being more accurate than just using a torque wrench.

But without more information, I can't tell you if these bolts are being tightned until they yield or not. You can design bolted joints so that the bolts are tightened unitl they yield slightly, or you can design joints so they do not tighten the bolts to yield.

But if the original poster has the book that says how to tighten the bolts, I am pretty sure it would say if the bolts should not be reused. My SWAG would be that tightening them 45 degrees, probably is not into yield. On the other hand, using new bolts ( of the correct grade )will never get you into trouble.

Dan

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