MrMark
Well-known member
I gotta say, in studying this, this is without any shadow of a doubt, the most misunderstood subject I have ever seen. The amount of false information is staggering.
Torque to Yield bolts on Calipers - Re-use or replace??
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KrisKustomPaint
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there are more important things to worry about than the grade of bolt holding your fender on.
MrMark
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Oh, I wasn't referring to your post, which I thought was correct. I hope you didn't think that. I was referring to the information I am seeing on the internet on this subject. It is mind blowing.
But, I would be worrying about the bolt holding my fender on.
KrisKustomPaint
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Oh, I wasn't referring to your post, which I thought was correct. I hope you didn't think that. I was referring to the information I am seeing on the internet on this subject. It is mind blowing.
But, I would be worrying about the bolt holding my fender on.
With vast amounts of information, comes vast amounts of ********.
Fords, F150s, Rangers, and Explorers. The bolt that holds the caliper to the spindle, that's what backed out while the wife was driving.
REAL HOT SCHITT
Banned
2 important words....... Discard & replace.
Yes, G8 caliper bracket to steering knuckle requires new TTY bolts torqued to 44 ft lbs and then tightened another 120 degrees.
Replacing just the pads doesn't require removing these bolts but I want to put on new rotors.
I assume TTY bolts are dealer only/special order? Would NAPA have a cross to a GM P/N.
I'm curious what brake shops do. I doubt they stock these specialty TTY fasteners.
zoomzoomjeff
Well-known member
I believe it's a different type of fastener.
Correct.
Again, I think it's a different bolt. You will know it when you see it. It's permanently stretched and if you try to thread it back in, it might just feel...."weird".
Then call me and every other technician a half-***. If you wrench long enough, you get to know approximate torque. For my brakes, I use loc-tite red and give a good torque by feel. Go hang out at your local dealership and see how many fasteners are torqued to spec. Head bolts and critical tolerance items like this, yes. Brake caliper to spindles, not so much.
With the exception being TTY brake bolts, then yes, I would use a torque wrench.
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MrMark
Well-known member
You are wrong on every count.
There are different fasteners for head bolt applications with thinned sections, for example, but most are just normal fasteners.
You should read some information and if you don't use a torque wrench on brakes you are half-assed and I couldn't care if you worked in a local dealer or not. Torque by feel is a complete joke. Your feel is probably off by miles.
They definitely are NOT torqued past yield because if they were they would have no clamping action to dynamic loading.
Does this work for you:
http://www.felpro-only.com/tec_notes/TEC TIP_T-T-Y Head Bolts.pdf
There are different fasteners for head bolt applications with thinned sections, for example, but most are just normal fasteners.
You should read some information and if you don't use a torque wrench on brakes you are half-assed and I couldn't care if you worked in a local dealer or not. Torque by feel is a complete joke. Your feel is probably off by miles.
They definitely are NOT torqued past yield because if they were they would have no clamping action to dynamic loading.
Does this work for you:
http://www.felpro-only.com/tec_notes/TEC TIP_T-T-Y Head Bolts.pdf
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RAYJAY
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x2 on this you can't even buy them for the v8 sho motor so you reuse them ......
Hurricane_Whisperer
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It does make sense. In order to understand this you will need to look at the stress strain graphs that are made when testing materials.
A test specimen is prepared. It is sort of dumbell shaped. The ends are big and the center section is turned down to a uniform size. The ends are then subjected to being pulled by a universal testing machine such as one made by Instron. http://www.instron.us/wa/home/default_en.aspx
You can see a stress strain diagram here: http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/Tensile.htm
In the initial phase of pulling the test specimen, the material is in the elastic region where the stress plotted against strain follows a straight line.
Once you hit the yield point the material will no longer snap back to its original size. It will however still snap back, just not all the way to the original length. If you look at the curve you will note that more force can still be applied to the tensile test specimen or in the case of the bolt, it will apply more force to the clamped components even when the material is no longer in the elastic region.
At some point the bolt will start to neck down and the force will decrease. If you keep applying force you will keep necking the bolt down and it will finally break at a lower force then need to get it to the Ultimate tensile strength.
Torque to yield bolts are indeed torqued until they actually do yield
See the faq from these people who make computer programs to calculate torque and bolting.
http://www.boltscience.com/pages/faq.htm#12
Hurricane_Whisperer
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You are not understanding the definition of yield POINT versus your concept of yielding or yielded. Yield point is the point, not region, but actual point on a stress strain graph where the material BEGINS to yield. Bolts are typically made from ductile not brittle materials so the region where the bolt will yield but not break is actually pretty large on a graph and it will continue to clamp.
That being said, I do believe that torque to yield bolts are usually torqued until they go just past the yield point. They don't try to keep tightening once the yield is detected.
Also true torque to yield is a method.
The reason why there is so much confusion on the issue is because here's what matters:
How tight does the bolt need to be?
Answer: Tight enough.
The manufacturer has found what tight enough is often through experience and experiment and that is why methods vary so much. They may not actually be tightening the bolt to yield. Or they may be in a region where some bolts will yield and others won't due to slight differences in strength. What matters is whether the bolted joint is reliable and that is not nearly as mysterious as all the methodology in arriving to the torque level or method they proscribe for the given joint. Each joint is unique, therefore you will find variance in what is referred to as torque to yield.
Hurricane_Whisperer
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That article specifically states that some bolts on some applications are torqued until they actually yield.
Others will be just shy of yielding. The thing is yielding may occur on a section of threads that won't be used, so it may be difficult to detect the yield. It is wise to throw the bolts away and use new ones.
MrMark
Well-known member
This and everything I have posted say you are wrong
http://books.google.com/books?id=3w...to yield bolts clamping force elastic&f=false
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MrMark
Well-known member
It's unclear in that. If you read the prior article by the engine rebuilder you will see that when a fastener is torqued right to the edge of yielding that dynamic engine loading (expansion) may take the bolt into the yield zone.
I'm not saying to reuse. I probably would get new but only because I am that way.
zoomzoomjeff
Well-known member
1--I have read some information on TTY.
2--I guess I'm half-assed by your definition then. I'll still fall asleep tonight. You may not think much of me, but you may want to call the race teams that hired me to build, disassemble and rebuild IndyCars to tell them they're all half-assed too since that's how majority of bolts are tightened. Not all, but the majority of them.
3--I didn't say I am currently working in a local dealership. Sorry if I inferred that. What I was saying is that if you walk into a local dealership, which would be one assumption of a workplace with properly trained, veteran technicians, you will most likely not see them break out the torque wrench for every operation they complete, including brake bolts to spindle. There's simply no time. Sure, my field service manual has torque ratings for just about every fastener on the vehicle. But to think that people break out the torque wrench and follow those specs on every operation is silly.
4--I'm not off by miles. I have checked my work periodically with a torque wrench out of curiosity, and I hand overtighten by ~10-20%.
Yes. It works for me. It didn't really sell your argument. I still believe they're both special fasteners AND the operation in which they are tightened.
What I get from you is that if a person doesn't torque each and every bolt to its factory manual specified setting....the car will explode. Most fasteners tightened today, in most settings, as a generalization, are hand tightened. By people who know what tight feels like. Period. And the world still turns. I don't have an interest ******* online anymore. Truthfully, I should be on here having fun. It's a nice forum, and I'd like to be part of the community doing something other than receiving insults from you.
For the record, yes, I would absolutely use a torque wrench on a torque to yield fastener because that's how that type of fastener works. 90% of the other fasteners on an entire vehicle, no.
MrMark
Well-known member
OK, let me throw this at you. I understand that the yield is not just a point that it is a section of the strain/stress curve. What if you go into plastic deformation by continued tighten past the elastic region, thereby exceeding the point where the bolt will return to its original length. You say this is acceptable because there is still spring back force and the bolt will still clamp and the curve shows that stress is maintained in the plastic region. As long as nothing moves (static) we are OK, we still have max clamping force.
However, at this point further elongation from dynamic loading (thermal expansion of the engine, for example)will cause further elongation of the bolt. If the bolt were below its yield point it would spring back completely. By contrast, in the yielded or plastic region where permanent deformation happens, the bolt will not spring back due to the dynamic loading.
It thus seems to me that in a dynamic environment (an engine) you need to keep the torque in the elastic range. I agree that when in a static environment that you could torque into the yielded range.
However, at this point further elongation from dynamic loading (thermal expansion of the engine, for example)will cause further elongation of the bolt. If the bolt were below its yield point it would spring back completely. By contrast, in the yielded or plastic region where permanent deformation happens, the bolt will not spring back due to the dynamic loading.
It thus seems to me that in a dynamic environment (an engine) you need to keep the torque in the elastic range. I agree that when in a static environment that you could torque into the yielded range.
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MrMark
Well-known member
Studies I have read and training show feel is often off by staggering amounts even by experienced mechanics - 40 percent or more. Brakes are a critical fastener they deserve a torque wrench. Tell the lady whose caliper came loose that you did it by feel when there was a torque spec.
MrMark
Well-known member
This post by GregH seems to sum it up well:
"Torque to yield bolts - be they head bolts, crank damper bolts, or in any other location - are a unique breed of bolt. They are single use bolts, very precisely crafted, and serve in only their designed location on the engine.
Two terms need to be defined. First one is torque. This is the force required to rotate a component. How hard do we have to pull on this wrench before the bolt is tight enough? A couple of things influence this: coefficient of friction between the head and the top of the workpiece, coefficient of friction between the threads and workpiece, and how close you are to the perpendicular of the bolt axis.
As a bolt is tightened, the bolt will stretch and twist. As long as the torque is relatively low, the stretch and twist are within the elastic limit of the bolt material. This means that if the force on the bolt is removed, then the bolt will immediately return to it's original shape. But, since some of the torque we apply to the bolt goes into twisting the bolt - which contributes nothing to the clamping action of the bolt - we have a hard time determining with precision the clamping force of the bolt at a given torque. Don't forget, friction between the bolt head and the workpiece is torque that is wasted as heat, and friction between the threads and the workpiece is wasted as heat and bolt twist. The only thing we really want is bolt stretch
This is where the "yield" portion comes in. When any material is deflected past the point where it returns to the previous shape when the force is released, it is said to have past it's elastic limit. This is the yield point. The elastic limit for a material can be accurately measured, and the material can be engineered to have a specific elastic limit.
These headbolts have a specific elastic limit. When we tighten up the bolts, we get progrssivly closer and closer to the elastic limit. The idea is to reach the limit at the end of the final torque sequence.
If you had a force gauge on a bolt as it is being tightened up to and past it's elastic limit, then you'd see the force increase linearly as the bolt is being tightened. Once the elastic limit is reached, the force plateaus and will not increase furthur. Eventually, if the bolt is tightened furthur, the bolt will fail.
So the head bolts are designed so the intended clamping load is equal to the elastic limit of the bolt. We tighten up the bolts to the elastic limit, and have achieved our intended clamp load with a high degree of accuracy.
Now the problems - the bolts are at the limit. This means that if an additional force increases the load on the bolt past the clamp load (read high cylinder pressure) then the bolt deforms some. Once the additional force is released, the bolt doesn't return to it's previous shape, and the clamp load exerted by the bolt is now less than it was before the additional force.
The elastic limit of a bolt changes with heat cycling. That's why we cannot reuse TTY bolts (among other reasons).
Head studs are designed to have an elastic limit far higher than that of TTY bolts. They will support much higher clamp loads than we put on them when torquing. If an additional force increases the clamp load, the stud will stretch, but will not surpass it's elastic limit. Therefore, once the additional force is released, the stud returns to it's previous shape, and the clamp load is retained. Since head studs do not rely on yield point, just torque, we have to provide a lubricant to the nut face and threads...
Hope this clears a few things up..."
http://www.thedieselstop.com/forums/f23/tighten-oem-head-bolts-172457/
"Torque to yield bolts - be they head bolts, crank damper bolts, or in any other location - are a unique breed of bolt. They are single use bolts, very precisely crafted, and serve in only their designed location on the engine.
Two terms need to be defined. First one is torque. This is the force required to rotate a component. How hard do we have to pull on this wrench before the bolt is tight enough? A couple of things influence this: coefficient of friction between the head and the top of the workpiece, coefficient of friction between the threads and workpiece, and how close you are to the perpendicular of the bolt axis.
As a bolt is tightened, the bolt will stretch and twist. As long as the torque is relatively low, the stretch and twist are within the elastic limit of the bolt material. This means that if the force on the bolt is removed, then the bolt will immediately return to it's original shape. But, since some of the torque we apply to the bolt goes into twisting the bolt - which contributes nothing to the clamping action of the bolt - we have a hard time determining with precision the clamping force of the bolt at a given torque. Don't forget, friction between the bolt head and the workpiece is torque that is wasted as heat, and friction between the threads and the workpiece is wasted as heat and bolt twist. The only thing we really want is bolt stretch
This is where the "yield" portion comes in. When any material is deflected past the point where it returns to the previous shape when the force is released, it is said to have past it's elastic limit. This is the yield point. The elastic limit for a material can be accurately measured, and the material can be engineered to have a specific elastic limit.
These headbolts have a specific elastic limit. When we tighten up the bolts, we get progrssivly closer and closer to the elastic limit. The idea is to reach the limit at the end of the final torque sequence.
If you had a force gauge on a bolt as it is being tightened up to and past it's elastic limit, then you'd see the force increase linearly as the bolt is being tightened. Once the elastic limit is reached, the force plateaus and will not increase furthur. Eventually, if the bolt is tightened furthur, the bolt will fail.
So the head bolts are designed so the intended clamping load is equal to the elastic limit of the bolt. We tighten up the bolts to the elastic limit, and have achieved our intended clamp load with a high degree of accuracy.
Now the problems - the bolts are at the limit. This means that if an additional force increases the load on the bolt past the clamp load (read high cylinder pressure) then the bolt deforms some. Once the additional force is released, the bolt doesn't return to it's previous shape, and the clamp load exerted by the bolt is now less than it was before the additional force.
The elastic limit of a bolt changes with heat cycling. That's why we cannot reuse TTY bolts (among other reasons).
Head studs are designed to have an elastic limit far higher than that of TTY bolts. They will support much higher clamp loads than we put on them when torquing. If an additional force increases the clamp load, the stud will stretch, but will not surpass it's elastic limit. Therefore, once the additional force is released, the stud returns to it's previous shape, and the clamp load is retained. Since head studs do not rely on yield point, just torque, we have to provide a lubricant to the nut face and threads...
Hope this clears a few things up..."
http://www.thedieselstop.com/forums/f23/tighten-oem-head-bolts-172457/
Hurricane_Whisperer
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From the Fel-pro article you linked to,
"On some engines, this stretching approaches the bolt's elastic limit and the bolts are permanently stretched."
It is pretty clear what that means. Permanently stretched.
I would say that the vast majority of bolts in automotive applications are probably not designed to be torqued until permanently stretched, but you have stated that a bolt taken past the yield point will no longer clamp which is untrue.
Some bolts are taken past the yield point. You are referring to automotive books that aren't about the basic bolt science while I have provide links for you explaining material testing, material properties and basic bolt science. I have actually ran those universal testing machines. In most automotive situations it is probably not practical to take a bolt to just past the yield point due to the expensive instruments required and lack of a need for such a highly stressed fastener in order to obtain the clamping force required.
In the high performance fasteners and plumbing article you should read the section entitled "precision instrumentation". It explains that computerized torque wrench instruments can be used to find the yield point. What matters in a bolted joint is clamping force and torque is a wildly inaccurate method of determining this. On most joints it is accurate enough. But where TTY bolting methods are used, torque is no longer accurate enough.
In the yield control mode, the torque instrument monitors the torque and angle. It will be able to sense when the bolt begins to yield because the torque and angle will cease to follow the relationship that is followed when the bolt is in the elastic zone.
http://www.k1technologies.com/RodBoltTechnology/tabid/80/Default.aspx
http://www.boltscience.com/pages/tighten.htm
Both of the above links describe methods of torque that take the bolt to just pass it's yield point where the torque is stopped.
The detection instruments can't detect the yield point until after just passing it.
While these methods aren't common, especially in automotive use because of the expensive instruments required, they have been used and torquing to just pass the yield point is a valid design used in some situations.
MrMark
Well-known member
Whisperer, I'm going to rest my case with this link. I am only a lawyer, after all. I think it settles it once and for all and is completely authoritative. You aren't considering the dynamic engine environment when you talk about the fastener being torqued beyond yield having maximum clamping force. I did keep this up my sleeve.
It is to be
pointed out that the torque-to-yield control method is mostly used
in critical applications, such as the automotive power train joints
for instance 4. For less critical applications, either the torqueonly
or the torque-turn control methods are often used.
Subsequent to its initial assembly, when a bolted joint is put in
service, it may be subjected to an external separating force, which
will increase the fastener tension and simultaneously reduce the
joint clamp load 5. In this study, the fastener has been initially
tightened beyond its elastic limit while the joint remained within
its elastic limit. Eventual removal of the joint separating force will
leave the fastener with a permanent set that will cause clamp load
loss.
http://www.ewp.rpi.edu/hartford/~ba...tener Elongation Beyond its Elastic Limit.pdf
Wisperer,
From your own link:
Yield Controlled Tightening
This method, developed by the SPS organisation, is also known under the proprietary name "Joint Control Method". Very accurate preloads can be achieved by this method by minimising the influence of friction and its scatter. The method has its roots in a craftsman's "sense of feel" on the wrench which allowed him to detect the yield point of the fastener with reasonable precision. With the electronic equivalent of this method, a control system is used which is sensitive to the torque gradient of the bolt being tightened. Rapid detection of the change in slope of this gradient indicates the yield point has been reached and stops the tightening process. This is achieved by incorporating sensors to read torque and angle during the tightening process. Since angle of rotation and torque are both measured by the control system, permissible values can be used to detect fasteners which lie outside their specification (having too low a yield for example).
Remember, I did agree with you that a fastener still provided max clamping force when taken beyond its yield point into plastic deformation. My point was that this was only for a static environment.
If I were the engineer specifying the clamping force I would design the bolt/method so that the fastener remained JUST BELOW the elastic limit to ensure maximum clamping force.
It is to be
pointed out that the torque-to-yield control method is mostly used
in critical applications, such as the automotive power train joints
for instance 4. For less critical applications, either the torqueonly
or the torque-turn control methods are often used.
Subsequent to its initial assembly, when a bolted joint is put in
service, it may be subjected to an external separating force, which
will increase the fastener tension and simultaneously reduce the
joint clamp load 5. In this study, the fastener has been initially
tightened beyond its elastic limit while the joint remained within
its elastic limit. Eventual removal of the joint separating force will
leave the fastener with a permanent set that will cause clamp load
loss.
http://www.ewp.rpi.edu/hartford/~ba...tener Elongation Beyond its Elastic Limit.pdf
Wisperer,
From your own link:
Yield Controlled Tightening
This method, developed by the SPS organisation, is also known under the proprietary name "Joint Control Method". Very accurate preloads can be achieved by this method by minimising the influence of friction and its scatter. The method has its roots in a craftsman's "sense of feel" on the wrench which allowed him to detect the yield point of the fastener with reasonable precision. With the electronic equivalent of this method, a control system is used which is sensitive to the torque gradient of the bolt being tightened. Rapid detection of the change in slope of this gradient indicates the yield point has been reached and stops the tightening process. This is achieved by incorporating sensors to read torque and angle during the tightening process. Since angle of rotation and torque are both measured by the control system, permissible values can be used to detect fasteners which lie outside their specification (having too low a yield for example).
Remember, I did agree with you that a fastener still provided max clamping force when taken beyond its yield point into plastic deformation. My point was that this was only for a static environment.
If I were the engineer specifying the clamping force I would design the bolt/method so that the fastener remained JUST BELOW the elastic limit to ensure maximum clamping force.
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Hurricane_Whisperer
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You are missing what is being said by that article. It's complicated but I am pretty sure I can explain it even to a lawyer. Only he must be more interested in learning than arguing however. I won't do it tonight, but I will give you a couple of hints to ponder.
The separation force has to be greater than the clamping force to result in stretching the bolt more.
Even in an joint where the bolts are in the elastic region, if the separation force exceeds the clamping force, you are in trouble because the joint comes apart and the bolts are subject to fatigue. They also now see the full force of the separation whereas they will not see the full separation force so long as the joint stays together.
If the bolts are torqued to yield, the clamping force is higher than if they weren't, therefore it may be possible for the bolts torqued to yield to have no problems as long as the bolt tension force exceeds the separation force and the joint therefore stays together.
Also note, that two cases are looked at: joints where the bolt is torqued to just past the yield point which is what we have been talking about and joints where the bolt is torqued significantly pass the yield point. I have stated that I doubt joints with the bolt torqued significantly past the yield point are used in the automotive world due to the lack of precision instruments and skill levels as well as a lack of basic necessity to do so.
MrMark
Well-known member
man, talk about stubborn. You are worse than any lawyer for arguing. I could bring down Jesus Christ himself and you would still tell me I don't understand after Jesus told you that they aren't torqued past yield.
I know this. I assume this to be true as should you.
Yes, I know this too. It argues that you should design the bolting appropriately, taking the torque as close to the yield point as possible, while remaining slightly under, as is done to my understanding.
Maybe, but that is not particularly relevant. It all depends on the situation and the design. I am discussing the situation where the separation force is potentially enough to exceed the bolt tension force as in an engine with gasketing.
You just can't admit you are wrong after I present you with incontrovertible proof of it.
No smart engineer would design a clamping system for a dynamic environment where separation forces could potentially exceed clamping forces with a bolting system having bolts stretched into plastic deformation. That would result in reduced and unpredictable loss in clamping forces. It is totally unnecessary to design a system that way. You are hung up on your machines. The only use of the machines here is in the lab to establish the procedure for specification to the field, e.g., 30 ft pounds plus 120 degrees to achieve a specific stretch. That doesn't have to be the point of yield, it can be just under.
I know this. I assume this to be true as should you.
Yes, I know this too. It argues that you should design the bolting appropriately, taking the torque as close to the yield point as possible, while remaining slightly under, as is done to my understanding.
Maybe, but that is not particularly relevant. It all depends on the situation and the design. I am discussing the situation where the separation force is potentially enough to exceed the bolt tension force as in an engine with gasketing.
You just can't admit you are wrong after I present you with incontrovertible proof of it.
No smart engineer would design a clamping system for a dynamic environment where separation forces could potentially exceed clamping forces with a bolting system having bolts stretched into plastic deformation. That would result in reduced and unpredictable loss in clamping forces. It is totally unnecessary to design a system that way. You are hung up on your machines. The only use of the machines here is in the lab to establish the procedure for specification to the field, e.g., 30 ft pounds plus 120 degrees to achieve a specific stretch. That doesn't have to be the point of yield, it can be just under.
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KrisKustomPaint
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just throw a breaker bar on it and tighten till it snaps then back it off a quarter turn.
yellowgt1vert
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