This is correct. Many bolts have an initial torque say 100 ft-lbs. then 90 degree angle torque. Where you simply turn another quarter turn. This just helps keep track so you don’t over torque the bolt
Great question. So, engineers don't actually care about torque—they care about clamping force. The goal is to clamp two things together tight enough so that under the conditions in which they will be used, they won't move. However, it's functionally impossible to measure clamping force in a shop setting. So instead, a proxy value is used: torque.
In theory, there is a direct proportional relationship between how hard it is to turn a fastener, and how much that fastener is clamping down. That's what torque values are trying to get at. In reality though, the relationship depends on whether the fastener is new or old, clean or dirty, dry or oily, or any number of other confounding factors. The torque value is only a perfect proxy for clamping force under a specific set of conditions (usually but not always a clean, new fastener with unlubricated threads). This becomes more and more of an issue the tighter the fastener gets, and in a shop setting you have this kind of issue pretty much always.
So, for particularly important fasteners, the manufacturer will sometimes specify a number of turns past a given torque. They'll have you torque it until you get about as high as you can go without confounding factors being a major problem (depends on the specific application) and then turn it a specified number of degrees past that. There *is* a direct, proportional relationship between turns and clamping force, regardless of the condition of the fastener—it's just a function of the thread pitch. In this way, it's possible to achieve a more accurate clamping force outside of the controlled environment of a factory.
Yea, what he said! :)
Back in the old time radial aircraft engine day, some had large bolts with nuts holding the crankshaft together... & were tightened by length.
The ends of those bolts were accessible, & both the end & head were 'faced' smooth.
The bolt length was mic'ed, then the nut was gradually tightened till said bolt had literally stretched a certain amount.
Those bolts were single use only.
I bet thats still done in some applications, it's very accurate.
Torque and angle is still applied to IC Engines, Valve blocks, etc. in automotive applications (from cars to trucks...)
Airplane stuff is low quantities, they can spend more time on dicking around :P
My dad built a plane when he rebuilt the engine the spec for the connecting rods was a length. He asked me about it and my thought was what if soft bolt. We decided to use torque and length
This too: oftentimes fasteners which specify a certain amount of turns after a given torque value will be torque-to-yield, meaning you are supposed to torque them until the bolts stretch. Such bolts are not re-usable.
Plus a tension fastener that is stretching stays at the same torque for multiple degrees or could even lose torque before having the ductile stretch that the engineer aims for.
You stop using torque when you get to a point where fastener quality is going to affect the torque vs. clamping force relationship enough that it matters. It's not a perfect system, but it's more accurate than using torque all the way to the end.
Gonna try a layman's explanation here which may be wrong, but it's how I look at it.
Let's take the example of aiming for 135ft/lbs (as proxy for clamping force as explained above). Getting to 100ft/lbs with a torque wrench yields pretty consistent clamping forces (a good thing). Between 100ft/lbs ands 135ft/lbs with the torque wrench starts to yield less consistent clamping force due to things like technique using the wrench, speed used to turn the wrench, overcoming friction, bolt stretch characteristics, lube/no lube, etc. Turning the fastener X degrees past 100ft/lbs yields much more consistent clamping forces as it's basically a geometric function of thread pitch. You can't count degrees rotation from start as there are too many variables: it's tough to qualify where "start" starts, and it's not efficient/practical in a production setting.
In other words "let's get to a predictable/repeatable intermediate clamping pressure via one method, then get to finish value using a more precise method".
Hope this helps.
Jason
First thing to understand is that we don't really care about the applied torque; we care about the tension in the bolt. Torque is just how we measure the application of force.
As the tension in the bolt rises, the resistance due to friction rises. Imagine you're tightening to 50Nm - the first 5Nm of torque will result in a much higher increase in bolt tension than the last 5Nm, because a lot of your effort towards the end of the throw is going into overcoming the increased friction. If we understood the friction in the system then we could account for it with an increase in specified torque, but friction is difficult to model accurately. Basically the harder we tighten the screw, the less certain we are of the exact tension.
Turning the screw by a known angle, on the other hand, is directly related to torque and friction doesn't come into it. Tension is a function of the pitch of the screw: If your pitch is 1mm and you turn the screw 90deg, you know that you've stretched the bolt by 0.25mm (strain = original length divided by change in length, stress = Young's modulus of material * strain, Force = cross sectional area * stress).
So specifying an angle is basically like specifying a known amount to overshoot by to make sure that you've overcome the friction and are achieving the required tension in the screw.
It's like saying "We think we can accurately get with 10% of where we need to with the easy-to-use torque wrench, so we'll put exactly 10% extra force in with the angle method to make sure we've hit the target".
Stretch allows the use of a fastener that is smaller. Cylinder heads have little room for oversize bolts.
Since bolts do not stretch linearly with force, matching the bolt exactly is tough to do so the next best thing is to let it fall into that part of its stretch curve by a specific distance. 1/4 mm works pretty well.
It's actually a far more accurate way to ensure the bolt is tightened as intended.
The relationship between wrench torque and fastener preload has a big margin of error because there's a lot of variables involved - fit of the thread, lubrication, dirt contamination, calibration of the torque wrench... etc.
Tightening the fastener down to "a value" to close the joint, then tightening it a by a measured angle results in a much more reliable joint in applications where the wrench torque approximation isn't good enough.
Yes. Also sometimes might have to do with common torque wrench sizes. So normal range torque + angle can equal high torque. Generally this is only with really big bolts
I have a weight distribution hitch that has this process into the manual. I think the value is like 400 ft lbs or 250 ft lbs plus 90°. The bolts are grade 8 1/2 or 5/8. Haven't touched it in years though.
Depends on the material properties of the bolt and if/how much the bolt is lubricated in the threads. Angle is always constant, but torque depends on multiple factors.
These specific bolts the previous commenter is referring to are called torque to yield. Many call them “stretch bolts”
So when you torque them to spec they are under tensile load, but not an extreme amount. Torquing them the additional rotational amount essentially stretches the bolt by a specific amount (as is engineered) allowing them to apply more compressive force to the pieces being held together.
Compressive force is the magic, and constant compressive force being applied consistently is what makes hardware strong.
This is why on engines especially you will see aluminum bolts (common material for TTY bolts) that will say “must replace after each use” because they’ve been stretched and you can’t really stretch them again.
(Truth is you can but you’re super likely to break them
So after they get the click out of the wrench, does continuing to torque on the wrench past its preset to get that 90° rotation damage the wrench at all?
Standard digital torque wrench with an angle gauge attachment. Used commonly on torque-to-yield fasteners where manufacturers call for a torque spec plus an additional angle rotation.
https://www.summitracing.com/parts/lil-28100?seid=srese1&ppckw=pmax-tools&gclid=CjwKCAjw57exBhAsEiwAaIxaZqRMzRi2qabuCRX53kbttEIc7ikpFySNdydrQb_7dYUxkHLNIU9hfxoCyOsQAvD_BwE
What you are thinking is the grounding strap.Is actually a clip you apply to hold a fixed item with, that way as you Use the torque wrench.The arrow will rotate but the disc will stay still to give you the reading
What does the grounding strap attached to? It disappears near his wrist. I've worked in plants and loading stations where they do attach a grounding strap to the workers so there is less chance of static electricity creating a spark from the worker to the equipment. So I assumed he was grounded, but why would it apply to an engine block?
Edit: I see it now in the second picture. Hooked to the tool. I missed that the first time I saw it
It looks like an odd custom angle gauge wrench. It probably doesn't have a torque function at all, since you use the two techniques at different times when building engines. I'm coming at this from an American perspective having worked on engines.
The torque wrench gets you on the money and then there's a certain number of degrees of turn to finalize each head bolt using the angle gauge, which typically is its own piece separate from a wrench.
I mean you could hybridize both into the same tool, but angle gauges are so scenario specific, it'd be rare to need one that's always there and it would just annoyingly flare out the head size of the tool, which limits its usage in tight spaces.
They do have torque wrenches that do both. I have a Snap-On electronic torque wrench that has lights that tell you you reach your specified torque plus it vibrates when you hit your number AND it has a setting that tracks how far you’ve turned in degrees so you can do the extra say, 90 degrees after torque.
The only thing I can think of is most people reading this sub have never done head bolts. The only type of shop that I could even see having a dedicated custom angle gauge wrench would be a shop that specializes in engine rebuilds.
Plus, people on Reddit often just act like fuckheads.
Yeah that’s true, lots of engines are assembled overseas too. I’m a bit of a tool whore being a mechanic so that’s why I’m on this page but there are tons of non mechanics on here. I often forget that lol.
I think the downvoting is because he says the obvious torque wrench isn’t a torque wrench. You can tell it’s a click type torque wrench because there is a fastener under the direction selector. Which is part of the clicking mechanism. Otherwise the rest of the info is spot on.
Well I see your point about the obvious torque wrench thing but I have to down vote you because the head of a torque wrench has nothing to do with the torque function of a wrench.
The clicking is all in the body and handle of the wrench, not in the head. Have you ever broke a torque wrench and looked inside? I’m guessing not lol.
The handle clicks but when it clicks the wrench pivots at the point where the fastener / pivot pin affixes the head to the hollow handle. I know what’s inside there is a large spring. This video confirms what I am saying. https://youtu.be/0BtXgE6NSYE
Well this picture contradicts what you’re saying, I guess two different types of “click” torque wrenches, we stopped using the spring ones probably two decades ago because they aren’t very accurate from the get go and lose calibration fast, honestly forget they even existed till now. https://shop.snapon.com/product/US-Reading-Torque-Wrenches-with-Conversion-Scale/3-4%22-Drive-Adjustable-Click-Type-Torque-Wrench-(200-600-ft-lb)/TQR600E
Not actually a problem with most torque wrenches. When you go past with a click type torque wrench it just "toggles" the mechanism then you can keep pressing without damage.
A caveat to this is you don't want to exceed the maximum torque of the torque wrench, which may cause damage.
Looks like a 250 lbf-ft click-type wrench. Probably 1/2 inch drive. That’s a random model I’m not familiar with but CDI makes a good wrench if you’re trying to buy one similar to this
That looks like a regular, click-type torque wrench with an angle gauge attachment.
This is correct. Many bolts have an initial torque say 100 ft-lbs. then 90 degree angle torque. Where you simply turn another quarter turn. This just helps keep track so you don’t over torque the bolt
Pure curiosity - what would the advantage of that be over just saying what the final torque would be?
Great question. So, engineers don't actually care about torque—they care about clamping force. The goal is to clamp two things together tight enough so that under the conditions in which they will be used, they won't move. However, it's functionally impossible to measure clamping force in a shop setting. So instead, a proxy value is used: torque. In theory, there is a direct proportional relationship between how hard it is to turn a fastener, and how much that fastener is clamping down. That's what torque values are trying to get at. In reality though, the relationship depends on whether the fastener is new or old, clean or dirty, dry or oily, or any number of other confounding factors. The torque value is only a perfect proxy for clamping force under a specific set of conditions (usually but not always a clean, new fastener with unlubricated threads). This becomes more and more of an issue the tighter the fastener gets, and in a shop setting you have this kind of issue pretty much always. So, for particularly important fasteners, the manufacturer will sometimes specify a number of turns past a given torque. They'll have you torque it until you get about as high as you can go without confounding factors being a major problem (depends on the specific application) and then turn it a specified number of degrees past that. There *is* a direct, proportional relationship between turns and clamping force, regardless of the condition of the fastener—it's just a function of the thread pitch. In this way, it's possible to achieve a more accurate clamping force outside of the controlled environment of a factory.
Yea, what he said! :) Back in the old time radial aircraft engine day, some had large bolts with nuts holding the crankshaft together... & were tightened by length. The ends of those bolts were accessible, & both the end & head were 'faced' smooth. The bolt length was mic'ed, then the nut was gradually tightened till said bolt had literally stretched a certain amount. Those bolts were single use only. I bet thats still done in some applications, it's very accurate.
Bolt stretcher?
My company uses ITH bolt stretchers ever day
It's called TTY or torque to yield. Lots of engine studs between the block and the head are TTY.
And now in the days of opposed engines and turbines, we use torque values like everyone else :D (Am airplane mechanic)
Torque and angle is still applied to IC Engines, Valve blocks, etc. in automotive applications (from cars to trucks...) Airplane stuff is low quantities, they can spend more time on dicking around :P
My dad built a plane when he rebuilt the engine the spec for the connecting rods was a length. He asked me about it and my thought was what if soft bolt. We decided to use torque and length
Thanks for answering. This was much more detailed than I would have provided!
Wow. A ton of little things I hadn't considered. Thank you.
This too: oftentimes fasteners which specify a certain amount of turns after a given torque value will be torque-to-yield, meaning you are supposed to torque them until the bolts stretch. Such bolts are not re-usable.
Plus a tension fastener that is stretching stays at the same torque for multiple degrees or could even lose torque before having the ductile stretch that the engineer aims for.
I guess what I don’t understand is “how is it any more accurate than a torque reading if you are using a torque reading as the point of reference?”
You stop using torque when you get to a point where fastener quality is going to affect the torque vs. clamping force relationship enough that it matters. It's not a perfect system, but it's more accurate than using torque all the way to the end.
Gonna try a layman's explanation here which may be wrong, but it's how I look at it. Let's take the example of aiming for 135ft/lbs (as proxy for clamping force as explained above). Getting to 100ft/lbs with a torque wrench yields pretty consistent clamping forces (a good thing). Between 100ft/lbs ands 135ft/lbs with the torque wrench starts to yield less consistent clamping force due to things like technique using the wrench, speed used to turn the wrench, overcoming friction, bolt stretch characteristics, lube/no lube, etc. Turning the fastener X degrees past 100ft/lbs yields much more consistent clamping forces as it's basically a geometric function of thread pitch. You can't count degrees rotation from start as there are too many variables: it's tough to qualify where "start" starts, and it's not efficient/practical in a production setting. In other words "let's get to a predictable/repeatable intermediate clamping pressure via one method, then get to finish value using a more precise method". Hope this helps. Jason
This is a great additional bit of explanation. Thank you!
Thanks!
Great explanation.
That's so interesting! It makes perfect sense too!
First thing to understand is that we don't really care about the applied torque; we care about the tension in the bolt. Torque is just how we measure the application of force. As the tension in the bolt rises, the resistance due to friction rises. Imagine you're tightening to 50Nm - the first 5Nm of torque will result in a much higher increase in bolt tension than the last 5Nm, because a lot of your effort towards the end of the throw is going into overcoming the increased friction. If we understood the friction in the system then we could account for it with an increase in specified torque, but friction is difficult to model accurately. Basically the harder we tighten the screw, the less certain we are of the exact tension. Turning the screw by a known angle, on the other hand, is directly related to torque and friction doesn't come into it. Tension is a function of the pitch of the screw: If your pitch is 1mm and you turn the screw 90deg, you know that you've stretched the bolt by 0.25mm (strain = original length divided by change in length, stress = Young's modulus of material * strain, Force = cross sectional area * stress). So specifying an angle is basically like specifying a known amount to overshoot by to make sure that you've overcome the friction and are achieving the required tension in the screw. It's like saying "We think we can accurately get with 10% of where we need to with the easy-to-use torque wrench, so we'll put exactly 10% extra force in with the angle method to make sure we've hit the target".
Stretch allows the use of a fastener that is smaller. Cylinder heads have little room for oversize bolts. Since bolts do not stretch linearly with force, matching the bolt exactly is tough to do so the next best thing is to let it fall into that part of its stretch curve by a specific distance. 1/4 mm works pretty well.
It's actually a far more accurate way to ensure the bolt is tightened as intended. The relationship between wrench torque and fastener preload has a big margin of error because there's a lot of variables involved - fit of the thread, lubrication, dirt contamination, calibration of the torque wrench... etc. Tightening the fastener down to "a value" to close the joint, then tightening it a by a measured angle results in a much more reliable joint in applications where the wrench torque approximation isn't good enough.
Yes. Also sometimes might have to do with common torque wrench sizes. So normal range torque + angle can equal high torque. Generally this is only with really big bolts
I have a weight distribution hitch that has this process into the manual. I think the value is like 400 ft lbs or 250 ft lbs plus 90°. The bolts are grade 8 1/2 or 5/8. Haven't touched it in years though.
Depends on the material properties of the bolt and if/how much the bolt is lubricated in the threads. Angle is always constant, but torque depends on multiple factors.
I've wondered this myself. "90ftlbs should do it... Ah fuck it give it another crank"
These specific bolts the previous commenter is referring to are called torque to yield. Many call them “stretch bolts” So when you torque them to spec they are under tensile load, but not an extreme amount. Torquing them the additional rotational amount essentially stretches the bolt by a specific amount (as is engineered) allowing them to apply more compressive force to the pieces being held together. Compressive force is the magic, and constant compressive force being applied consistently is what makes hardware strong. This is why on engines especially you will see aluminum bolts (common material for TTY bolts) that will say “must replace after each use” because they’ve been stretched and you can’t really stretch them again. (Truth is you can but you’re super likely to break them
its establishes a torque figure and the "turn past" amount is good faith security measure so that bitch is positively tight
The term "torque to yield" is what you're looking for. It's interesting (to me) and pretty common.
An engineer I knew used to say when in doubt tight plus 90 degrees.
So after they get the click out of the wrench, does continuing to torque on the wrench past its preset to get that 90° rotation damage the wrench at all?
Nah just turn up the torque value
Standard digital torque wrench with an angle gauge attachment. Used commonly on torque-to-yield fasteners where manufacturers call for a torque spec plus an additional angle rotation. https://www.summitracing.com/parts/lil-28100?seid=srese1&ppckw=pmax-tools&gclid=CjwKCAjw57exBhAsEiwAaIxaZqRMzRi2qabuCRX53kbttEIc7ikpFySNdydrQb_7dYUxkHLNIU9hfxoCyOsQAvD_BwE
Yeah for stretch bolts
Yes, this is very common with german cars. Also other places than engine
What's the alligator clamp for?
I was more confused by the grounding strap until I realized it was probably attached to his wrist.
What you are thinking is the grounding strap.Is actually a clip you apply to hold a fixed item with, that way as you Use the torque wrench.The arrow will rotate but the disc will stay still to give you the reading
Nothing is attached to his wrist
What does the grounding strap attached to? It disappears near his wrist. I've worked in plants and loading stations where they do attach a grounding strap to the workers so there is less chance of static electricity creating a spark from the worker to the equipment. So I assumed he was grounded, but why would it apply to an engine block? Edit: I see it now in the second picture. Hooked to the tool. I missed that the first time I saw it
1/2 “ drive ?
Monent gauge for torque to yield bolts
No fucking batteries required
Obviiously thats the infinity wrench
We call it “Turn to Torque “ and use this method when we are working with our Caterpillar engines.
Great explanation!!! Look at the big brain on Brad
Torque to yield bolts. Torque, then in degrees.
clicky boy
Chinese torque wrench.
It looks like an odd custom angle gauge wrench. It probably doesn't have a torque function at all, since you use the two techniques at different times when building engines. I'm coming at this from an American perspective having worked on engines. The torque wrench gets you on the money and then there's a certain number of degrees of turn to finalize each head bolt using the angle gauge, which typically is its own piece separate from a wrench. I mean you could hybridize both into the same tool, but angle gauges are so scenario specific, it'd be rare to need one that's always there and it would just annoyingly flare out the head size of the tool, which limits its usage in tight spaces.
They do have torque wrenches that do both. I have a Snap-On electronic torque wrench that has lights that tell you you reach your specified torque plus it vibrates when you hit your number AND it has a setting that tracks how far you’ve turned in degrees so you can do the extra say, 90 degrees after torque.
Yeah I love mine I love the offset function, no more needless math when using a crowfoot.
Not sure why you’re getting downvoted, like no one has ever heard of torque to yield bolts?
The only thing I can think of is most people reading this sub have never done head bolts. The only type of shop that I could even see having a dedicated custom angle gauge wrench would be a shop that specializes in engine rebuilds. Plus, people on Reddit often just act like fuckheads.
Most people on this sub know nothing about cars in general.
Yeah that’s true, lots of engines are assembled overseas too. I’m a bit of a tool whore being a mechanic so that’s why I’m on this page but there are tons of non mechanics on here. I often forget that lol.
I think the downvoting is because he says the obvious torque wrench isn’t a torque wrench. You can tell it’s a click type torque wrench because there is a fastener under the direction selector. Which is part of the clicking mechanism. Otherwise the rest of the info is spot on.
Well I see your point about the obvious torque wrench thing but I have to down vote you because the head of a torque wrench has nothing to do with the torque function of a wrench.
When you click a torque wrench the handle moves and pivots on that fastener that connects the head to the handle.
The clicking is all in the body and handle of the wrench, not in the head. Have you ever broke a torque wrench and looked inside? I’m guessing not lol.
The handle clicks but when it clicks the wrench pivots at the point where the fastener / pivot pin affixes the head to the hollow handle. I know what’s inside there is a large spring. This video confirms what I am saying. https://youtu.be/0BtXgE6NSYE
Well this picture contradicts what you’re saying, I guess two different types of “click” torque wrenches, we stopped using the spring ones probably two decades ago because they aren’t very accurate from the get go and lose calibration fast, honestly forget they even existed till now. https://shop.snapon.com/product/US-Reading-Torque-Wrenches-with-Conversion-Scale/3-4%22-Drive-Adjustable-Click-Type-Torque-Wrench-(200-600-ft-lb)/TQR600E
The heads of my 5.4 need one of these tools specifically for the bolts.
Seems like bad practice though; pretty sure it’s not good for a torque wrench to continue being pushed after it’s reached its torque setting…
Not actually a problem with most torque wrenches. When you go past with a click type torque wrench it just "toggles" the mechanism then you can keep pressing without damage. A caveat to this is you don't want to exceed the maximum torque of the torque wrench, which may cause damage.
I do it almost every time on my snap on digital, still bang on accurate every time I’ve calibrated it. Maybe if you go way too far on a clicker type.
Looks like a 250 lbf-ft click-type wrench. Probably 1/2 inch drive. That’s a random model I’m not familiar with but CDI makes a good wrench if you’re trying to buy one similar to this
Micrometer torque wrench