Torque Threshold: Shearing Bolts / Breaking Tools

[oldschoolcraft]

I plan on reviewing the science/physics of torque this week for fun. One thing I always wondered is, whether a certain tool is truly needed or if the torque generated will be so high that it will shear the fastener.

And in some cases, the fastener is so seized, that removing it might exceed the threshold of the tool.

For examples, suppose you have a seized fastener and put a 3/8" long reach ratchet on it. You might snap the anvil on the ratchet. Whereas maybe a 3/8 breaker bar can sustain more torque than the ratchet, and could have broken it for you.

I guess this doesnt matter too much to professional mechanics where it's better to occasionally break a tool and warranty it, rather than constantly change tools out of fear of breaking one, and wasting time. Time = money. But for me, I am not a pro, and I might be able to warranty something in a week or two, but I only have one car and I need to fix it right now, and if my tool breaks I'm kind of screwed.

So what I'd like to find some rough calculations or estimations for:

• How much torque before you shear the bolt head off a bolt, for various sized bolts?
• How much torque before you deform a bolt when you put too much torque on a nut?
• How much torque before you break the anvil on a ratchet? I think there's ANSI standards, and I have seen Project Farm videos where he tests different ratchets.
• How much torque before you break the anvil on a breaker bar?
• How long of a cheater pipe can I add to something before I'm just going to shear the bolt off or break the tool anyway?

Part of this is fun to review science, but part of is to figure out "when should I change tools?" and also "how many tools do I really need?" Also maybe once I have a better understanding of torque numbers, I can watch Project Farm and have it be more meaningful to me.

There's a second issue, one of access, whereby maybe you want a longer tool for better access, not necessarily more torque. So of course, we need every possible sized tool that exists even if it might shear the fastener if used to max possible torque, because of access.

 

[cody1325]

I was recently fixing a gate, using a SK 45175 3/8" ratchet with a Craftsman "Made in Texas" 1/2" socket on the end. Without hardly any force (OK, OK, I probably had tightened it a little TOO much, but it didn't feel tight) the entire bolt sheared off in the nut, requiring me to have to grab an old screwdriver and a hammer to unjam my socket.

Maybe I was used to the torque put out by my much shorter 45170.

 

[2ndGearRubber]

For metric automotive quality hardware, 2x install torque is where your breakage gets pretty high. For instance an M8x1 bolt, caliper pins, is usually torqued around 20ftlb. Around 40, you'll see failures. Most m6x1, 10mm head, stuff will be 120inlb max, so ~10ftlb. Failure becomes almost guaranteed at 20 ftlb.

Your margin for error goes up with larger hardware. Although you may not achieve proper clamping force it can be difficult to shear an M16 axle bolt, or an M30 axle nut. The flats on the hardware just can't apply enough torque to do so. That's the secret behind breaking bolts, and needing torches. Often one cannot apply enough torque to the head to loosen the hardware, before the hardware fails. Alignments are a good example of this. You need an open end wrench for the jam nut. After rust and crust, there is a break away force required much higher than install torque. If two flats cannot deliver that torque, they will round or otherwise fail before the nut turns. It's not a matter of torque applied, it's a matter of maximum torque which can be transfered.

 

[oldschoolcraft]

I think there might be some concept whereby it's not just a linear application of torque, but maybe the pulse of torque that could be considered? Maybe putting 2X the fastener torque is fine, if it's just a quick pulse, which is how I think an impact gun works. That might be why I hear people say impacts can help you break loose fasteners that you would shear off by hand? It makes sense now that I think about it.

Not sure what the technical term would be for the pulse of torque.

 

[Hannahranga]

Avoiding long reach 3/8 ratchets helps, I've got a 3/8" breaker bar if I snap that it's cheap enough and pretty clear sign I should have used a 1/2" breaker. Iirc a 3/8 anvil shouldn't snap before 150ftlbs.

 

[chevy.stroker]

On installation stretching the threads from over torquing is a very real issue. This reduces clamping force.

You can often easily stretch threads without over torquing if you apply a lubricant when the bolt should be dry. As an experiment place a 3/8 UNC bolt in a vice, clean the threads and a nut with brake clean, and torque the nut to spec. Remove the nut and check the thread with a thread pitch gauge. Repeat the same, but oil the bolt. The threads will often be streched.

 

[AEAdam]

On installation stretching the threads from over torquing is a very real issue. This reduces clamping force.

No it doesn’t. Clamping force continues to rise. This is how torque to yield bolts work. I guess it proportionately reduces if that’s what you meant. If you graphed torque (y axis) vs preload x axis, you’d get a fairly straight line up to the point of plastic yield. At that point the slope would become shallower, but would still rise.

You can often easily stretch threads without over torquing if you apply a lubricant when the bolt should be dry. As an experiment place a 3/8 UNC bolt in a vice, clean the threads and a nut with brake clean, and torque the nut to spec. Remove the nut and check the thread with a thread pitch gauge. Repeat the same, but oil the bolt. The threads will often be stretched.

1) You shouldnt be able to plastically yield a bolt by torquing to its “spec”, unless the specified torque is torque to yield (TTY).
2) Dry torque values represent clean hardware, lightly lubed with oil or dry film lube. Not bone dry.
3) Assuming we are talking about bolted joints (which are not super common on cars) as opposed to a machine screw, you can totally stretch a bolt's threaded region by overtorquing.

Dry hardware causes stick slip. If you actually performed the experiment above, you’d find the dry samples would either have no thread deformation or lots of thread deformation. The bolt stretch on the oiled hardware would be more similar, which is what you want.

 

[AEAdam]

First, know that torque is a terrible way to predict preload. Up to 80% of the torque you apply is lost in friction. Angles are better.

Second, most people don’t understand how their torque wrenches work or how to use them properly. In some instances, poor technique can render the use of the tool pointless.

• How much torque before you shear the bolt head off a bolt, for various sized bolts?

This depends on the grade of the bolt. I think that chart of mine (that should be sticky) has target torque values for different grade bolts.

• How much torque before you deform a bolt when you put too much torque on a nut?

If you apply much over the torque values from my chart, you are probably deforming it. Std torques are pretty close to yield.

• How much torque before you break the anvil on a ratchet? I think there's ANSI standards, and I have seen Project Farm videos where he tests different ratchets.

Dont know the ANSI std off the top of my head, but Snap On says their Dual 80 ratchets meet the following:
1/4” 90ftlbs
3/8” 250ftlbs
1/2” 750ftlbs

• How much torque before you break the anvil on a breaker bar?

Same as above.

• How long of a cheater pipe can I add to something before I'm just going to shear the bolt off or break the tool anyway?

Manufacturers are pretty careful about ratchet and breaker bar lengths. Snap On is particularly aggressive with their LL ratchets. They try not to make ratchets so long that normal people can easily break stuff with them. It’s best to stick with those lengths.

Likewise, they limit socket sizes for each drive. That’s why serious toolmakers don’t make 19mm sockets for 1/4” drive. So the answer is, buy a decent long ratchet and never put a pipe on it, if you do, you greatly Increase your risk of breaking something.

Snap On is a very serious toolmaker with an actual engineering dept. I would use them as your reference for socket sizes and ratchet lengths. They know what they are doing.

I don’t think I’d ever put a cheater bar on 3/8” drive. I assume I can pretty easily put 100lbs on the end of a tool. Since I bought the SHLF80, I don’t recall using a cheater bar.

 

[rooster59]

Everything assumes old school nuts & bolts made in Ohio, NY, etc., made properly from real steel. If you buy bolts at HD, hardware store, etc. box usually says something like “country of origin Mexico, Taiwan, Korea, India, Pakistan”. This means they are probably made in Pakistan in an open air garage, 1922 machines, using metal.

 

[CapriMikeC]

If you are nerdy enough, there's excellent info in Machinery's Handbook. All information will assume new never-been-used fasteners.

 

[Hohn]

I plan on reviewing the science/physics of torque this week for fun. One thing I always wondered is, whether a certain tool is truly needed or if the torque generated will be so high that it will shear the fastener.

And in some cases, the fastener is so seized, that removing it might exceed the threshold of the tool.

For examples, suppose you have a seized fastener and put a 3/8" long reach ratchet on it. You might snap the anvil on the ratchet. Whereas maybe a 3/8 breaker bar can sustain more torque than the ratchet, and could have broken it for you.

I guess this doesnt matter too much to professional mechanics where it's better to occasionally break a tool and warranty it, rather than constantly change tools out of fear of breaking one, and wasting time. Time = money. But for me, I am not a pro, and I might be able to warranty something in a week or two, but I only have one car and I need to fix it right now, and if my tool breaks I'm kind of screwed.

So what I'd like to find some rough calculations or estimations for:

• How much torque before you shear the bolt head off a bolt, for various sized bolts?
• How much torque before you deform a bolt when you put too much torque on a nut?
• How much torque before you break the anvil on a ratchet? I think there's ANSI standards, and I have seen Project Farm videos where he tests different ratchets.
• How much torque before you break the anvil on a breaker bar?
• How long of a cheater pipe can I add to something before I'm just going to shear the bolt off or break the tool anyway?

Part of this is fun to review science, but part of is to figure out "when should I change tools?" and also "how many tools do I really need?" Also maybe once I have a better understanding of torque numbers, I can watch Project Farm and have it be more meaningful to me.

There's a second issue, one of access, whereby maybe you want a longer tool for better access, not necessarily more torque. So of course, we need every possible sized tool that exists even if it might shear the fastener if used to max possible torque, because of access.

I suggest reading this short bolting 101 thing here or if you REALLY want to get into this, find the Kamax Bolt and Screw Compendium pdf online. You'll need some free time for that one.

There's a simple equation that governs bolt tension relationships: T=FKD

T= Torque in Nm or lb-ft
F= Force in Newtons or Pounds
K= "nut factor" or "k-factor", a dimensionless unit that relates rotational torque to axial bolt stretching force
D= Diameter in the same units of length as your torque unit. (Ft or Meters typically).

It's useful to remember that a bolt thread is just a ramp wrapped around a cylinder. You can think of the nut factor as sort of the angle of that ramp. The lower the nut factor, the higher is the fraction of torque that goes into stretching the bolt instead of into twisting it. Bolts become more "efficient" in the sense of translating torque into stretch. This is why many people assume that finer threaded fasteners need less torque for the same amount of bolt stretch. (they would if not for the higher friction that more than offsets this and causes finer threads to need MORE torque for the same stretch)

As friction rises, the bolt becomes less efficient at converting torque to stretch, so the fraction of torque that goes into stretch is lessened. Which means the rest of that input had to go somewhere-- and it goes into twisting the bolt.

So you can think of the nut factor as the "balance point" that allocates the input torque between stretching and twisting. Higher nut factor, less stretching and more twisting.

It's like the ramp angle in the sense that the ramp angle determines how much of the input energy is going to force vs distance (in the equation of work=force * distance). It's the same total amount of work, but the split of force and distance won't be the same in all cases).

Torque is often thought of as a form of work. Both are force times distance, it's just that one is rotational and the other is linear.


I don't think anyone can give you meaningful answers to your questions. If you are working on rusty hardware frequently, I would suggest you get the following useful assistants and add them to your tools:

--Thread chasing taps/nuts (the Lang set is a godsend)
--a "bolt breaker" attachment for an air hammer. This turns a socket into a .401 air hammer tool. It allows you to apply some rotational torque with a wrench while the air hammer is pounding on the bolt head or adjacent to it. I use chrome sockets and turn the air pressure down so I'm not annihilating my sockets (I feel like the harder chrome is more effective at transmitting hammer blows). Repeated hammering blows are the only thing I have found consistently able to break loose the most stubborn fasteners without catching things on fire.
- Some "rocket sockets"-- I use the Topec knockoffs that are cheaper and excellent from Amazon. These are best for rounded external hexes.
- Some good internal extractors like the RBRT or Grip Edge


There's just no substitute for wrench time IMO in developing a "feel" for what is right for a fastener and what is too much. And I would disagree about breaking a tool vs damaging the part. I can have replacement tools in a trip into town. Replacement hardware-- especially on the Honda/Toyotas I own-- is not exactly a hardware store item. It's worth it to me to damage a tool if it means saving the part.

That said, I believe it's a false dichotomy. I don't think I've broken a hand tool in 35 years of wrenching. Busted lots of knuckles, but not the tools. Tools now are better than ever and unless one found a way to buy the worst of the worst, a broken tool is largely operator error IMO.

 

[chevy.stroker]

Since I apparently don't know what I'm talking about:

Lubricated Bolts and Reduced Torque

Lubrication effect on bolt tension and torque.

www.engineeringtoolbox.com

If you torque a bolt specified to be dry to the same torque oiled then the threads will permanently stretch. Thus clamping force will reduce.

 

[Hohn]

Since I apparently don't know what I'm talking about:

Lubricated Bolts and Reduced Torque

Lubrication effect on bolt tension and torque.

www.engineeringtoolbox.com

If you torque a bolt specified to be dry to the same torque oiled then the threads will permanently stretch. Thus clamping force will reduce.

Not necessarily will the threads permanently stretch. But it's possible. I was once able to drastically neck down a bolt well before it got to the "proper" torque because the dry film coating on it was much slipperier than expected. Dry film-- no oil.

Nor is it the case that clamping force will be less. Most bolted joints are engineered to achieve a load that's about 80% of the nominal yield of the fastener. If you push it into 100% of yield, you have INCREASED the clamping force.

Torque to yield fasteners are very common now where they fasteners are yielded *on purpose* during assembly. This causes the fasteners to be single-use-only.

That "k-factor" is the source of the sensitivity of the torque to tension relationship. You might assume that you have a value of 0.18 for a manganese phosphate coated fastener into cast iron. But if you have Black oxide as the coating, the factor might change to 0.21. Stainless tends to gall so you'll need some kind of anti-seize and the factor might be 0.14.

As materials and coatings change, the value changes. And that tiny change from, say 0.18 to 0.22 is actually a change of 22%! That's pretty huge, actually. That's the difference between 100 lb-ft and 122 lb-ft.

A heavily rusted fastener might end up at 0.4 or 0.5 or higher. That's a massive increase in friction compared to what was engineered into the virgin parts.

 

[rust in the eye]

"And in some cases, the fastener is so seized, that removing it might exceed the threshold of the tool."
You are in California, what seized automotive fasteners could you be encountering?
I don't think that even Toyotas with their PlayDoh fasteners* rust out there.
No need to overthink this. All but the crappiest tools are strong enough to break free appropriately sized (to the tool) fasteners. Slipping and busting knuckles is another subject.
* against my better judgement I helped a friend with his Toyota truck over the weekend, a simple three bolt job, two broke and required drill and re-tap. Reminded again why I loathe working on Japanese cars. As I told him, well engineered and well built but from garbage steel.

 

[Firebrick43]

I have never had a long length modern dual 80 fail yet even when used as a breaker in 3/8 or 1/2”. Similarly the L872 ratchet has never broken in use even with a 42” handle and long cheater pipes but I have put a kit in it as the ratchet pawl started hanging up after lots of abuse.

They will exceed the strength of many breaker bar that I have broken such as an Armstrong or especially a craftsman breaker. I have broken maybe 5 or 6 craftsman breakers, all but one spread the forks of the breaker and only one shearing the anvil. I did (3) 3/4 breakers trying to change a truck tire on the side of the road about a mile from a sears store years ago.

I have deposited all craftsman ratchets and breakers in the trash as a result.

 

[chevy.stroker]

I will try one more time.

I only mentioned a 3/8 UNC bolt because it is the easiest to see and identify the stretch.

I did not mention torque to angle process or torque to yield bolts (TTY), but will here.


Critical bolts in a newer engine such as main bolts use a torque to angle process. This is because of the friction issue mentioned above. Torquing to a lower spec reduces the affect of the friction and then the angle twist stretches the bolt without permanent distortion correctly. Because with rod bolts you can usually access both ends of the bolt you use a stretch gauge.

TTY bolts are specially designed to stretch to yield generally using the torque to angle process. This is to clamp 2 dissimilar metals together. An aluminum cylinder head, composite gasket, and cast iron block expand at different rates and TTY removes the bolts ability to over stretch during expansion and then not be able to shorten during contraction. Again these bolts are specifically design for their purpose.


I also did not mention bolt material. ARP bolts with a higher tensile strength are generally torqued to a higher value than an OE bolt

 

[richfinn]

I plan on reviewing the science/physics of torque this week for fun. One thing I always wondered is, whether a certain tool is truly needed or if the torque generated will be so high that it will shear the fastener.

And in some cases, the fastener is so seized, that removing it might exceed the threshold of the tool.

For examples, suppose you have a seized fastener and put a 3/8" long reach ratchet on it. You might snap the anvil on the ratchet. Whereas maybe a 3/8 breaker bar can sustain more torque than the ratchet, and could have broken it for you.

I guess this doesnt matter too much to professional mechanics where it's better to occasionally break a tool and warranty it, rather than constantly change tools out of fear of breaking one, and wasting time. Time = money. But for me, I am not a pro, and I might be able to warranty something in a week or two, but I only have one car and I need to fix it right now, and if my tool breaks I'm kind of screwed.

So what I'd like to find some rough calculations or estimations for:

• How much torque before you shear the bolt head off a bolt, for various sized bolts?
• How much torque before you deform a bolt when you put too much torque on a nut?
• How much torque before you break the anvil on a ratchet? I think there's ANSI standards, and I have seen Project Farm videos where he tests different ratchets.
• How much torque before you break the anvil on a breaker bar?
• How long of a cheater pipe can I add to something before I'm just going to shear the bolt off or break the tool anyway?

Part of this is fun to review science, but part of is to figure out "when should I change tools?" and also "how many tools do I really need?" Also maybe once I have a better understanding of torque numbers, I can watch Project Farm and have it be more meaningful to me.

There's a second issue, one of access, whereby maybe you want a longer tool for better access, not necessarily more torque. So of course, we need every possible sized tool that exists even if it might shear the fastener if used to max possible torque, because of access.

The trouble your going to run into in your scientific endeavor is rust, all bets are off when your dealing with corroded metal fasteners unfortunately.

This is one of the reasons auto mechanics are so obsessed with impact tools, once you have developed "The Feel" you just know how much leverage is too much and switch your method of removal before it's too late.

A longer lever isn't always the right answer!!!

There isn't really any solid scientific data behind the following video (but we've all been there multiple times), but the key take aways are

1. He is using a practice piece to experiment with.

2. He is using a tool designed for removing delicate fasteners (Diesel glow plugs) that regularly break using conventional tools.

3. He starts at a low setting and works his way up.

 

[VolvoRyan]

Hate to say it, as I'm a scientist by trade....... but book learning is pretty useless here.

Feel and experience are everything. Add in some creativity and a good contingency plan.

-Ryan

 

[Hohn]

"And in some cases, the fastener is so seized, that removing it might exceed the threshold of the tool."
You are in California, what seized automotive fasteners could you be encountering?
I don't think that even Toyotas with their PlayDoh fasteners* rust out there.
No need to overthink this. All but the crappiest tools are strong enough to break free appropriately sized (to the tool) fasteners. Slipping and busting knuckles is another subject.
* against my better judgement I helped a friend with his Toyota truck over the weekend, a simple three bolt job, two broke and required drill and re-tap. Reminded again why I loathe working on Japanese cars. As I told him, well engineered and well built but from garbage steel.

I own a 2011 GX460 the spent its first 13 years in Chicago. It has a lot of rusty hardware.

Yet none have broken on me. I've replaced several of them just to have some unrusted parts and to make sure it goes together better. But I've not had a rusted bolt break on disassembly.
Perhaps it's not *entirely* the grade of the Toyota hardware, but also the tools and techniques used.

 

[PoorOwner]

Use a breaker bar if it doesn't seem like the ratchet can do it. I can usually detect a bit of flex in the drive or extension, then it is time to upsize 3/8 to 1/2, or 1/2 to 3/4.

 

[engineer2]

I like to simplify things. This does not apply to TTY bolts.

 

[vwpieces]

Here is one for ya...
55ft/lbs on a 3/8-16 Grade 9 bolt.
On a Quincy QT-5 pump.



Granted I made mistake and used lube. Also the third time used.


Max torque value i could find anywhere is 48ft/lbs dry for G9. They got 45ish on New dry bolts.
Expensive suckers New too... Washers G9 too.

 

[AEAdam]

Not a direct response but hopefully some good info: Torque isn't theory. Torque values were generated by industry and my company specifically based on testing 100 years ago. The problem has always been the calculations for friction.

When we say "dry torque" we mean no grease, locktite, or sealant applied. "Dry" doesn't mean chalky, corroded or degreased with brake clean. We don't have ANY hardware in our factories that fit those descriptions. And we specifically did not generate test data to support people working on their own cars. Dry could mean (does mean) dry film lube. It also means wet with oil or wax used by the manufacturers to protect against corrosion. Typically, in aircraft maintenance, we either test or discard removed hardware. So fastener corrosion isn't really a thing for us. And we are where the rest of the industry got their data.

If you are applying huge wet fastener knockdowns (ours are more like 10%, not 50%), you'd better know what you are doing. If I can provide one piece of advice that I think would help everyone this is it:

Work CLEAN. Because torque is greatly impacted by friction, ALWAYS make sure the threads are clean, no grit. The faying (mating) surfaces must be clean and the area under the head must be clean. You should not be feeling grit dirt, hearing anything grinding. A light film of oil (like 3in1) on the threads and especially under the head does not justify the use of wet torque values. You can apply a little oil and feel comfortable you won't over stretch the bolt if you know how to use a torque wrench.

Couple torque wrench tips:
1) We exercise our clickers 4 times after resetting the torque value to ensure any oil inside the wrench is distributed. Might be overkill for auto shops, but if you haven't used your torque wrench in 7 months, think about it
2) Must hit the target torque while moving. We have a minimum of 90 degree turn prior to hitting the target. You cannot "check" torque on a static bolt. That provides less than zero usable data (no its not the minimum the bolt is torqued to).
3) You stop pulling at just as the wrench releases. If you pull through the click, you over torqued it. If you do it again for good measure, you did even worse, dumb ***. Loosen the bolt and start over.

 

[AEAdam]

I like to simplify things. This does not apply to TTY bolts.

TTY is between "Oh ****" and "Ultimate". We used to stop before "oh ****", before yield. In that initial "good region", the bolt had (near) infinite life.

The reason automotive has gone to TTY is the need for additional clamping force when mating parts (especially Aluminum heads) heat up. In the old days, the growth due to heat (plus combustion pressure) would push the bolt beyond yield into the plastic deformation region. When the engine cooled, the bolt could have little clamp up and oil leaks resulted.

In the plastic range, a decent amount of extra load doesn't really stretch the bolt much and we still have plenty of capability before we get to ultimate. You also have simply more clamping force above yield. The closer you get to ultimate, the less elongation you get by adding tension.

 

[Kurt4440]

Hate to say it, as I'm a scientist by trade....... but book learning is pretty useless here.

Feel and experience are everything. Add in some creativity and a good contingency plan.

-Ryan

Same here, and I couldn't agree more with you.

When I was an undergraduate, I would fix cars for extra money, none of my fellow engineering students knew anything about cars.

 

[rust in the eye]

I own a 2011 GX460 the spent its first 13 years in Chicago. It has a lot of rusty hardware.

Yet none have broken on me. I've replaced several of them just to have some unrusted parts and to make sure it goes together better. But I've not had a rusted bolt break on disassembly.
Perhaps it's not *entirely* the grade of the Toyota hardware, but also the tools and techniques used.

Nope, ain't my first rodeo with rusty stuff. It's the garbage fasteners they use.

 

[Wakefield]

I suggest reading this short bolting 101 thing here or if you REALLY want to get into this, find the Kamax Bolt and Screw Compendium pdf online. You'll need some free time for that one.

There's a simple equation that governs bolt tension relationships: T=FKD

T= Torque in Nm or lb-ft
F= Force in Newtons or Pounds
K= "nut factor" or "k-factor", a dimensionless unit that relates rotational torque to axial bolt stretching force
D= Diameter in the same units of length as your torque unit. (Ft or Meters typically).

It's useful to remember that a bolt thread is just a ramp wrapped around a cylinder. You can think of the nut factor as sort of the angle of that ramp. The lower the nut factor, the higher is the fraction of torque that goes into stretching the bolt instead of into twisting it. Bolts become more "efficient" in the sense of translating torque into stretch. This is why many people assume that finer threaded fasteners need less torque for the same amount of bolt stretch. (they would if not for the higher friction that more than offsets this and causes finer threads to need MORE torque for the same stretch)

As friction rises, the bolt becomes less efficient at converting torque to stretch, so the fraction of torque that goes into stretch is lessened. Which means the rest of that input had to go somewhere-- and it goes into twisting the bolt.

So you can think of the nut factor as the "balance point" that allocates the input torque between stretching and twisting. Higher nut factor, less stretching and more twisting.

It's like the ramp angle in the sense that the ramp angle determines how much of the input energy is going to force vs distance (in the equation of work=force * distance). It's the same total amount of work, but the split of force and distance won't be the same in all cases).

Torque is often thought of as a form of work. Both are force times distance, it's just that one is rotational and the other is linear.


I don't think anyone can give you meaningful answers to your questions. If you are working on rusty hardware frequently, I would suggest you get the following useful assistants and add them to your tools:

--Thread chasing taps/nuts (the Lang set is a godsend)
--a "bolt breaker" attachment for an air hammer. This turns a socket into a .401 air hammer tool. It allows you to apply some rotational torque with a wrench while the air hammer is pounding on the bolt head or adjacent to it. I use chrome sockets and turn the air pressure down so I'm not annihilating my sockets (I feel like the harder chrome is more effective at transmitting hammer blows). Repeated hammering blows are the only thing I have found consistently able to break loose the most stubborn fasteners without catching things on fire.
- Some "rocket sockets"-- I use the Topec knockoffs that are cheaper and excellent from Amazon. These are best for rounded external hexes.
- Some good internal extractors like the RBRT or Grip Edge


There's just no substitute for wrench time IMO in developing a "feel" for what is right for a fastener and what is too much. And I would disagree about breaking a tool vs damaging the part. I can have replacement tools in a trip into town. Replacement hardware-- especially on the Honda/Toyotas I own-- is not exactly a hardware store item. It's worth it to me to damage a tool if it means saving the part.

That said, I believe it's a false dichotomy. I don't think I've broken a hand tool in 35 years of wrenching. Busted lots of knuckles, but not the tools. Tools now are better than ever and unless one found a way to buy the worst of the worst, a broken tool is largely operator error IMO.

I wonder if the predicted breakage torque valve would vary between an SAE fine 3/8" capscrew "bolt" threaded into a tapped hole of sufficient depth for the shank not to bottom out before the capscrew head makes contact with the washer or whatever it abuts vs. a case where the tapped hole is too shallow for the length of the "bolt" so that it stops turning before beginning to achieve clamping force? (assuming both "bolts" are grade 8) (usually have 9/16" wrench size hex heads) - like blade mounting hardware for a mower

 

[Wakefield]

TTY is between "Oh ****" and "Ultimate". We used to stop before "oh ****", before yield. In that initial "good region", the bolt had (near) infinite life.

The reason automotive has gone to TTY is the need for additional clamping force when mating parts (especially Aluminum heads) heat up. In the old days, the growth due to heat (plus combustion pressure) would push the bolt beyond yield into the plastic deformation region. When the engine cooled, the bolt could have little clamp up and oil leaks resulted.

In the plastic range, a decent amount of extra load doesn't really stretch the bolt much and we still have plenty of capability before we get to ultimate. You also have simply more clamping force above yield. The closer you get to ultimate, the less elongation you get by adding tension.

How helpful is it to add extra length of unthreaded portion of bolt subject to stretch between the threaded part (inside of the threaded/tapped hole) and the area where clamp force is applied - like making the passage through the cylinder head longer or using multiple washers or even bushings in order to accommodate a longer bolt?
Also "Belleville Washers" do they help? Does a Belleville washer always require a thick/high grade flat washer under it in use? (Tecumseh Engines used to use Belleville Washers over a flat washer on the cylinder head bolts on some of their larger air cooled mower engines)

 

[Steve_P]

So, I won't debate anything above but will post some facts. This is all for new fasteners.

For a reusable fastener, torque value is determined in order to reach about 70% of the bolt's tensile yield. So, based on this, you can see that an identical TTY fastener will achieve ~40% more clamping force for no additional cost. Yay! See, it's not a conspiracy to sell more fasteners, which wouldn't even be a rounding error in Toyota's revenue.

Based on this, for a Grade 5/ class 8.8 fastener, you need about 2X the spec'd torque to reach the ultimate tensile strength and break ****. Shockingly, not, this is about what SecondGearRubber said above. And I'm using math. So, yes, math, theory... still has validity. OMG!

For Grade 8/class 10.9 it's about 1.8X the torque to reach UTS. Again, more validity.

Carry on.

 

[2ndGearRubber]

Not a direct response but hopefully some good info: Torque isn't theory. Torque values were generated by industry and my company specifically based on testing 100 years ago. The problem has always been the calculations for friction.

When we say "dry torque" we mean no grease, locktite, or sealant applied. "Dry" doesn't mean chalky, corroded or degreased with brake clean. We don't have ANY hardware in our factories that fit those descriptions. And we specifically did not generate test data to support people working on their own cars. Dry could mean (does mean) dry film lube. It also means wet with oil or wax used by the manufacturers to protect against corrosion. Typically, in aircraft maintenance, we either test or discard removed hardware. So fastener corrosion isn't really a thing for us. And we are where the rest of the industry got their data.

If you are applying huge wet fastener knockdowns (ours are more like 10%, not 50%), you'd better know what you are doing. If I can provide one piece of advice that I think would help everyone this is it:

Work CLEAN. Because torque is greatly impacted by friction, ALWAYS make sure the threads are clean, no grit. The faying (mating) surfaces must be clean and the area under the head must be clean. You should not be feeling grit dirt, hearing anything grinding. A light film of oil (like 3in1) on the threads and especially under the head does not justify the use of wet torque values. You can apply a little oil and feel comfortable you won't over stretch the bolt if you know how to use a torque wrench.

Couple torque wrench tips:
1) We exercise our clickers 4 times after resetting the torque value to ensure any oil inside the wrench is distributed. Might be overkill for auto shops, but if you haven't used your torque wrench in 7 months, think about it
2) Must hit the target torque while moving. We have a minimum of 90 degree turn prior to hitting the target. You cannot "check" torque on a static bolt. That provides less than zero usable data (no its not the minimum the bolt is torqued to).
3) You stop pulling at just as the wrench releases. If you pull through the click, you over torqued it. If you do it again for good measure, you did even worse, dumb ***. Loosen the bolt and start over.

I'm not sure what biz you work in, but I would say 90 degrees is impossible for most automotive bolts. Nothing in the suspension like arm mounts, or wheel bearing bolts. Can't be done without ignoring the service manual process and disassembling the entire subframe out of the car.

That's why I hate angles, because the engineering dept will spec something stupid like 40 degrees and I can only twist the bolt 3 clicks of a dual80 at a time with it connected to a 2ft extension. Unless it's a divisive of normal angles, 90, 180, etc it's stupid and a bad design. Even 45 can be a bit dicey. For -most- automotive stuff, non engine internals for example, it literally doesn't matter from a functional perspective. 1 year difference, same bolts, knuckle, and bearing, but now with angle! It's around 125ftlb the year prior. Frankly anything between 90 and 150 isn't going to matter.


My father was an engineer, well, still has his PE. As he transitioned into management of a utility and oversaw the entire start to finish process of building power plants he told me "you need deadlines, or engineering will just engineer it forever. It's what makes us engineers". Angles, IMO, are "cool story bro". It does NOT require angles to secure an m10 bolt for a caliper bracket. Factually not required. That's what drives me nuts about it. It's "better" but we don't need better, it's fine, just bolt the thing on there, it's fine. Head bolts? Hollow oil control bolts? Sure, totally fine. Within 10 years we will have angle specs for lug nuts and drain plugs. Would the clamping load be more consistent? 100%. Does it actually need to be?

 

[2ndGearRubber]

Nope, ain't my first rodeo with rusty stuff. It's the garbage fasteners they use.

I like toyotas but some of their hardware *****. The stuff actually on the drive train is great, but things like fuel tank strap bolts ****.

In the rust belt, basically every single under car fastener goes in with grease or anti sieze on the shanks, not threads, to fight getting rusted into a bushing or similar. I have worked on some things so rusted and rotten that the threads, shanks, and under the bolt head ALL get moly grease or anti sieze. IDK what it does to the torque value since I'm usually tightening by hand, but those alignment cam bolts will NEVER freeze on my watch!

 

[Kurt4440]

Nope, ain't my first rodeo with rusty stuff. It's the garbage fasteners they use.

Toyota fasteners don't seem bad if you have ever worked on Italian cars from the 1970's.

 

[AEAdam]

I'm not sure what biz you work in, but I would say 90 degrees is impossible for most automotive bolts. Nothing in the suspension like arm mounts, or wheel bearing bolts. Can't be done without ignoring the service manual process and disassembling the entire subframe out of the car.

Because of access? Don't worry about the 90. Just make sure the hardware is moving when you hit the target. If you hit the target on a stationary bolt, you literally have nothing, no idea where that bolt is torque-wise.

That's why I hate angles, because the engineering dept will spec something stupid like 40 degrees and I can only twist the bolt 3 clicks of a dual80 at a time with it connected to a 2ft extension. Unless it's a divisive of normal angles, 90, 180, etc it's stupid and a bad design.

Don't have a tech wrench? This is what a tech wrench is for. Shouldn't matter what the angle is.

My father was an engineer, well, still has his PE. As he transitioned into management of a utility and oversaw the entire start to finish process of building power plants he told me "you need deadlines, or engineering will just engineer it forever. It's what makes us engineers". Angles, IMO, are "cool story bro". It does NOT require angles to secure an m10 bolt for a caliper bracket. Factually not required. That's what drives me nuts about it. It's "better" but we don't need better, it's fine, just bolt the thing on there, it's fine. Head bolts? Hollow oil control bolts? Sure, totally fine. Within 10 years we will have angle specs for lug nuts and drain plugs. Would the clamping load be more consistent? 100%. Does it actually need to be?

Angles are smart because they isolate friction from preload. I predict you will see them more and more often.

 

[Death Row Dave]

Old Timers on the pipeline crews “ smoke tight : tighten till she smokes and back off 1/4 turn all is good to go “

 

[2ndGearRubber]

Because of access? Don't worry about the 90. Just make sure the hardware is moving when you hit the target. If you hit the target on a stationary bolt, you literally have nothing, no idea where that bolt is torque-wise.

Don't have a tech wrench? This is what a tech wrench is for. Shouldn't matter what the angle is.

Angles are smart because they isolate friction from preload. I predict you will see them more and more often.

If the techangle can only turn say 10 degrees at a time, and the socket/head interface is 2 degrees, and the 2ft extension has 8, I can't turn the bolt. Service info just states "bruh use a torque wrench and totally just tighten it to spec" even though there is zero ability to do so within the physical dimensions available. IME with a fixed torque spec you can do so in a slightly tighter area, although there are always situations where the fastener 100% cannot be torqued in place per service info process. The only time I "double hit" fasteners is when I have a sealing surface compressing and I go over multiple times through the pattern to make sure everything stayed tight. Can't do that with angle, which is less than ideal, but large surfaces like valve covers or timing covers typically aren't angle applications.


I 100% agree angles create a more precise clamping force. My assertion is that the proliferation of angles is simply because of engineering "because we can" rather than an inability to hold a wheel hub on with 4 M12 fine thread bolts. That hub doesn't -need- angle. It's "better" and "more correct", but 10 years ago we held a similar sized hub, with similar hardware, less angles. Per my example prior, angle specs may come out for a given model year despite the previous year using identical parts and part numbers having a fixed torque number. And the hubs didn't fall off, and the new stuff doesn't have the hubs lasting longer.

Which is cool and all, I'm all for better clamping force. So long as it can actually be done in place. Otherwsie - booooooo angles ****. That, and the funky angles, which I dont think any self respecting engineer is actually okay with nonsense like prime numbers being used as angle specs.

 

[rust in the eye]

In the rust belt, basically every single under car fastener goes in with grease or anti sieze on the shanks, not threads, to fight getting rusted into a bushing or similar. I have worked on some things so rusted and rotten that the threads, shanks, and under the bolt head ALL get moly grease or anti sieze. IDK what it does to the torque value since I'm usually tightening by hand, but those alignment cam bolts will NEVER freeze on my watch!

I often do this too. I figure have mercy on the next guy as it could be me.

 

[Hohn]

The reason automotive has gone to TTY is the need for additional clamping force when mating parts (especially Aluminum heads) heat up. In the old days, the growth due to heat (plus combustion pressure) would push the bolt beyond yield into the plastic deformation region. When the engine cooled, the bolt could have little clamp up and oil leaks resulted.

In the plastic range, a decent amount of extra load doesn't really stretch the bolt much and we still have plenty of capability before we get to ultimate. You also have simply more clamping force above yield. The closer you get to ultimate, the less elongation you get by adding tension.

That's not quite why TTY is done. Based on the reasoning you outline here, your aluminum heads would take the fastener farther into yield when they heated up and then you'd lose quite a bit of clampload when things cooled off. In other words, if it worked as you described, it would be counterproductive and produce less load in the joint after the first hot cycle took things farther into yield. This is why exhaust manifold bolts are always breaking and/or falling out-- they yield when hot and relax when cold.

TTY actually isn't done for more clamping per se. In most applications, you could just go to the next size larger fastener or the next higher grade material, install with more torque and you'd get more clamp load. Don't have enough clamp load with an 8.8 or 9.8 M10 at 45Nm? Bump up to 10.9 at 65Nm. 10.9 still fretting? Try a 12.9 at 80Nm if it's under the valve cover and oil wetted. That kind of thing.

No, the main advantage of TTY is that is improves the consistency of bolt loading, especially in bolt patterns where evenness of load really matters. Think head bolts, but also rods and mains, flywheel bolts, etc.

Torque is a proxy value for stretch, but it has imperfect correlation. Stretch is what we care about, not torque per se. Torque is just a means to an end for when we can't measure stretch directly with acceptable convenience or cost.

Normal straight torque can have a torque/tension scatter of ±30% (at 3 sigma) even with all clean new hardware and a calibrated torque wrench of good quality.

Torque plus angle can reduce the torque/tension scatter to ±15%. This is a massive improvement.

But TTY is much better still, because the yield point is defined by the metallurgy and not by local friction variables. Basically TTY eliminated the nut factor as a variable and replaces it with a fixed constant (if you want to think of it that way). TTY can slash the torque tension scatter to ±8% or so. Metallurgy still varies from batch to batch and heat treat lot to heat treat lot, but the metallurgy varies a lot less than the local friction conditions do. Hence the huge improvement in consistency in bolt load.

Moreover, alloys for TTY fasteners are designed in such a way that they are very ductile and have a "soft knee" on the yield curve. This means that when you assemble them in a production environment with DC tooling giving you real-time feedback of torque and angular position, the controller on the DC tool knows very precisely JUST when the fastener starts to yield (it's plotting the torque tension curve in real time as it tightens and then stopping once it hits some amount of deviation from that best fit, sometimes at the 0.2% offset that actually defines most Yield strength values).

The TTY bolted joint will be laid out in such a way that the existing clamp load should never take the bolt farther into yield. It's more helpful perhaps to think of TTY as "torque until it JUST starts to yield".

The only bolt fastening tech that improves on TTY for consistency is pretensioning-- typically done with large specialty hydraulic tools that can achieve <5% torque/tension variation. Those joints just pull the fastener to nearly its yield point, then the nut is spun down to a very low torque value and the tension on the fastener is released. This isn't practical in small automotive fasteners and blind holes, but it's the standard practice on structural bolting (think bridges and buildings) and other critical bolted joints where you need the absolutely most consistently loading and TTY isn't good enough or impractical because of the high resultant torque values.

In smaller bolted joints where you have access to the backside (i.e not blind), you'd just measure the stretch with a mic and torque to a given stretch value because that's far more consistent than any torquing procedure.

 

[Hohn]

Not a direct response but hopefully some good info: Torque isn't theory. Torque values were generated by industry and my company specifically based on testing 100 years ago. The problem has always been the calculations for friction.

When we say "dry torque" we mean no grease, locktite, or sealant applied. "Dry" doesn't mean chalky, corroded or degreased with brake clean. We don't have ANY hardware in our factories that fit those descriptions. And we specifically did not generate test data to support people working on their own cars. Dry could mean (does mean) dry film lube. It also means wet with oil or wax used by the manufacturers to protect against corrosion. Typically, in aircraft maintenance, we either test or discard removed hardware. So fastener corrosion isn't really a thing for us. And we are where the rest of the industry got their data.

If you are applying huge wet fastener knockdowns (ours are more like 10%, not 50%), you'd better know what you are doing. If I can provide one piece of advice that I think would help everyone this is it:

Work CLEAN. Because torque is greatly impacted by friction, ALWAYS make sure the threads are clean, no grit. The faying (mating) surfaces must be clean and the area under the head must be clean. You should not be feeling grit dirt, hearing anything grinding. A light film of oil (like 3in1) on the threads and especially under the head does not justify the use of wet torque values. You can apply a little oil and feel comfortable you won't over stretch the bolt if you know how to use a torque wrench.

Couple torque wrench tips:
1) We exercise our clickers 4 times after resetting the torque value to ensure any oil inside the wrench is distributed. Might be overkill for auto shops, but if you haven't used your torque wrench in 7 months, think about it
2) Must hit the target torque while moving. We have a minimum of 90 degree turn prior to hitting the target. You cannot "check" torque on a static bolt. That provides less than zero usable data (no its not the minimum the bolt is torqued to).
3) You stop pulling at just as the wrench releases. If you pull through the click, you over torqued it. If you do it again for good measure, you did even worse, dumb ***. Loosen the bolt and start over.

Great post, and this is precisely why I have to laugh to myself when someone breaks out the torque wrench to reinstall rusty old hardware to "factory torque specs."

Even under ideal conditions, straight torque can vary ±30% so if you have radically different friction than the lab-grade conditions under which that spec was developed, you might have error of 60% or more. The result is insufficient preload. That's why when working on old vehicles, "gudenteit" by an experienced hand can actually be BETTER than the following the torque spec from the manual.

A short example of this:

I was the development engineer on a new diesel engine with high pressure common rail plumbing, which is somewhat exotic in terms of its design and material. I was called down to the test cell because the high pressure lines were leaking (not entirely surprising at 2400 bar, but I digress). They replaced the lines and it fixed the problem. When after the 3rd time reinstalling the same lines, they would leak again. And of course, the conscientious technician had dutifully tightened the nuts to the proper torque spec.

The problem was that the nut/line interface was galling when it was disassembled. So the friction value was rising every time the line was reused. Informally, you could witness this because the new line would take nearly a full rotation to go from "snug" to torque spec and each time it was reused, the degrees of rotation to hit the "Spec" would decrease until eventually it was barely a 1/4 turn.

So I developed a torque+angle equivalent for them to use in the test cell when reusing lines (reuse is generally a bad idea, but new ones when constantly swapping injectors on a test engine get expensive fast, especially when they're prototypes). By the 3rd torqueing of the same parts, the resulting torque to hit the correct load rose by over 50%.

A redesign to address the galling was ultimately required, but it was an eye-opening experience for me to see just how radically the surface condition and friction can affect the joint and render the "proper" toque spec worse than useless-- it was dangerous.