How much should I adjust torque when using anti-seize?

[YoshiMoshi]

TL;DR Summary

How much should I adjust torque when using anti-seize?

Rust belt fasteners on cars that have been in use for about 20 years, sometimes seize up and snap inside of their holes. I would like to avoid the frustration going forward of this happening by using anti-seize. How much should I adjust torque specifications by when using anti-seize? Looking online, I can't seem to really get a clear answer. Everybody seems to have their own opinions on this matter. A common recommendation online is to reduce torque by about 25 %. Seems kind of scary to use anti-seize, if you can't determine how you should adjust the torque. It would seem to be pretty much useless. So I would like to figure it out.

This is for Toyota fasteners that fit into one of three categories. Toyota fasteners have their own specifications. Their head markings are not ones that you can find at hardware stores or auto parts stores.

1. Carbon steel bolt and alloy steel bolt
2. Non heat treated type high strength bolt
3. Boron steel bolt

I believe torque is calculated via

T = K D P

• The desired clamp load, P, is not known by me as the end user.
• However, the ideal specified torque, T, for nearly all bolts for my vehicle is specified by the service information.
• D can be measured and is the diameter of the bolt
• The K value that was used while determining the torque specification is unknown to me as the end user. However, looking online, most torque specifications assume a clean bolt that is not lubricated. If the torque specification is made assuming the bolt is lubricated before assembly, than the service information would likely specify to apply a specific lubricant on the threads before assembly.

Even with the unknowns, I can determine a ratio, assuming I'm using the same bolt in both instances, and the desired clamping load remains the same.

If:
T_Dry = K_Dry D P
T_Anti-Seize = K_Anti-Seize D P

Then:
T_Anti-Seize / T_Dry = (K_Anti-Seize D P) / (K_Dry D P)
T_Anti-Seize / T_Dry = K_Anti-Seize / K_Dry

Finally:
T_Anti-Seize = (T_Dry K_Anti-Seize) / K_Dry

Looking online, the K value is not typically specified by anti-seize manufactures. However I did find one specified value, https://www.antiseize.com/Content/Images/techdata/td11000.pdf. The Anti Seize Technology company makes a copper and graphite anti-seize compound whose K value is "0.172 +/- 0.009" in accordance with ISO 16047.

Assuming slightly over torquing a fastener would be better than slightly under torquing the fastener, I would go with the 0.172 + 0.009 value or 0.181.

Looking online at some websites, it seems like 0.2 is a good estimate for dry torque, non-lubricated fasteners. If this was the case, then I would reduce my torque by 10 %, when using Anti-Seize Technology COP-GRAF, to achieve the same clamp load as an unlubricated bolt.

Another common anti-seize manufacturer is Permatex. I couldn't find the K factor on the datasheets for their products, but I think they would likely give it to me if I asked (maybe).

Now my question becomes, is 0.2 a good assumption to make for non lubricated bolts? What value should I be using instead if not?

 

[jack action]

If you really want to know for sure, for your actual parts, you can test it by measuring the bolt stretch which is the true end effect of preload.

Take your bolt and nut (or one of similar material and diameter), apply the dry torque, and measure the bolt length. Repeat the process by lubricating the part and torque it until you reach the exact same bolt length. This new torque is the torque required for that particular bolt, nut, and lubricant.

Rod Bolt Stretch Gauges: The Right Tools for Measuring Bolt Stretch​

 

[Baluncore]

If you really want to know for sure, for your actual parts, you can test it by measuring the bolt stretch which is the true end effect of preload.

True.

If you want to calculate the required torque, then there are several things that will need to be known.
1, 2. Friction coefficient between the threads, dry and lubricated.
3, 4. Friction coefficient between the nut, or screw head, turning against the workpiece, dry and lubricated.
5. Thread pitch, which determines torque required on the helical thread, to stretch the shank.

 

[YoshiMoshi]

Thanks!

I don't think I will be able to find the friction coefficients between the threads or between the nut and screw thread. The manufacturer of the anti-seize product isn't going to know that, but the manufacturer of the vehicle, and I doubt they would provide that. It probably exists somewhere in a drawing that is intellectual property.

So test and measuring seems like a more practical approach. How can I accomplish this when I don't have a physical nut separate from the joint? I think the term may be "blind hole"? Where I have a piece that already has a pre drilled hole which is threaded, and I only have access to one side of the hole. For example, valve cover bolts, where the "nut" is inside the the engine. It's like you said, where I would have to use a physical nut of a similar material?

But I think I understand the concept where if I have a physical nut and bolt, and have access to both sides. I can apply the specified torque for this particular bolt and nut from the service information, dry. Spin the nut all the way down to the head of the bolt. Hold the nut or head of the bolt still, while applying the appropriate torque on the part I'm not holding still using a torque wrench. Now measure the length. Apply whatever lubricant I want, and apply torque until I get approximately the same length.

Would I have to to take this measurement while installed in the work piece though? Say for example McPherson strut assemblies. There are two brackets towards the bottom of the assembly. The knuckle goes in-between the brackets. A bolt goes in one side and the nut on the other to fasten the two together. Would I need to take my measurements with this measuring tool once completely assembled?

Or is it ok for me to take this measurement by just using the previous method by just tightening down the nut and bolt with nothing in-between?

My gut instinct tells me that the metal brackets on the McPherson assembly and the knuckle would provide some extra resistance to clamping down on it. But I don't that would necessarily matter?

I appreciate the help!

 

[jack action]

For example, valve cover bolts,

First, I don't think you should you crazy with such non-critical bolts. Even the "torque" method isn't that precise, especially when used with dirty, rusty parts.

So you could use a nut - maybe homemade? - made of the same material.

Would I have to to take this measurement while installed in the work piece though?

Of course, the closer you are to the original setup, the better it is. If you read the link in my previous post, even setting the same torque on two similar bolts, mounted in the same manner, may not give the same elongation. Still, what matters is that all bolts have stretched by the same amount (ideally in percentage of original length), not that they have the same torque.

The torque results in an axial force that will give the desired preload and the corresponding elongation. The relationship between the two is only a matter of radius and friction as said in post #3, not what they are squeezing together. Although having a similar final thickness will be better. (Elongation relative to original length is better than absolute length difference.)

This is why bolt manufacturers can provide a recommended torque value for their bolts, no matter how you intend to use them.

The elongation you measured should represent the strain just before the yield point in a stress-strain diagram; keeping it in the elastic region. (Although, some one-time-use bolts go slightly above, being plastically deformed, hence the reason why they have to be thrown away and replaced when disassembled.) The axial force $F$ for the corresponding stress would be the one used to calculate the torque required.

 

[YoshiMoshi]

Hey thanks!

Instead of a homemade nut, would an alternative approach be, to mark the bolts? I have also seen differing opinions on this matter. But it seems like if I torque a bolt down according to specification from the manufacture of the vehicle, mark with a straight line on the head of surface of the bolt and onto the piece I'm fastening together.

I can then unfasten the same bolt, hand tighten the bolt down. Then pull out a torque wrench and torque it down to the same value. The mark on the head of the bolt and the piece I'm working on "should" line up to the same exact spot, perhaps even count how many revolutions (if more than one) the lines go pass each other for future reference for below.

Could this mark indicate the same clamping load, even if I used anti-seize? I would assume so, seems pretty logical. This would be a much easier method. Essentially do the same thing again but put anti-seize on the threads of the bolt. Get the head of the bolt flush with the piece, and then tighten it down until the lines meet up (ensuring that I went around as many revolutions as I did before if it was more than once).

 

[gmax137]

First, I don't think you should you crazy with such non-critical bolts. Even the "torque" method isn't that precise, especially when used with dirty, rusty parts.

I agree. I think @YoshiMoshi is overthinking this, at least for most of the nuts and bolts he's likely to access without tearing the engine down. And, I wouldn't go through the car removing and re-installing fasteners just to get never seize on them. And finally, if you are going to go through the exercise, I'd recommend oiling most of the threads, rather than never-seize.

 

[YoshiMoshi]

I agree. I think @YoshiMoshi is overthinking this, at least for most of the nuts and bolts he's likely to access without tearing the engine down. And, I wouldn't go through the car removing and re-installing fasteners just to get never seize on them. And finally, if you are going to go through the exercise, I'd recommend oiling most of the threads, rather than never-seize.

Ah why oil vs anti-seize?

No way not every bolt lol. Just as a go forward basis when I need to remove parts for maintenance as they brake.

 

[gmax137]

Ah why oil vs anti-seize?

Well, never-seize can be a real mess, it gets everywhere (hands, clothes, face...) lol. I only use it for dissimilar metals, like steel studs threaded into aluminum. I know some people do use it on wheel lug nuts and spark plugs. Plus, I think the manufacturer's torque specs are usually for lightly oiled threads. The manual providing the specs should really say if they're for dry or oiled threads.

No way not every bolt lol. Just as a go forward basis when I need to remove parts for maintenance as they brake.

Ok, that makes sense.

 

[jack action]

Get the head of the bolt flush with the piece, and then tighten it down until the lines meet up

That is basically the "angle method" and it is independent of friction:

To explain how torque angle works, we need to work backward. Engineers first determine the desired clamp load for the items. Once they know that, they can run the numbers based on fastener size and material to determine the required bolt stretch to achieve that clamp load. From there, it’s simply a matter of taking the thread pitch of the fastener and determining how many degrees of rotation are required for the fastener to be stretched the desired amount.

You may have to be careful with this method if there is a soft gasket involved. (especially when changed)

That being said, I kind of use the angle method for most of my bolts and nuts (and, yes, big fan of anti-seize):

The way to tighten "by feel" with a power tool is to quickly seat the nut and then give it a ¼ turn or so; you kind of "see it" tightening and get a feel for the angle you need with experience. It's a little bit like using a torque angle measurement.

You don't just put the tool on it and tighten it as much as the tool can give because, yes, you can overtighten it easily, maybe even breaking the stud.

The only place I have used a torque wrench - or any other measuring method - is with engine bolts, such as the ones for the cylinder head or the crankshaft, maybe the intake manifold.

 

[jrmichler]

An excellent article, originally published in Sport Aviation magazine, on bolt torque, bolt friction, thread lubrication, and clamp force: https://resources.savvyaviation.com...s_eaa/EAA_2014-06_cylinder-work-be-afraid.pdf.

The author is Mike Busch, an expert aircraft mechanic who has published many articles on aircraft maintenance.

 

[Ranger Mike]

Bolts are for clamping things together. Not locating something. Water will invade and cause rust no matter what you do and how you try to prevent it. By the time rust gets too bad on a shock or strut the strut will belong gone in usefulness. Assemble the bolt and clamp dry and clean and torque it t spec and forget about it. My Ford tractor has been out side in weather for 30 years that I have owned it, ( it is a 1953 model ) so totally exposed to the elements. Some bolts tuff to remove but all come out with no drilling if you know how. If you want to do something, paint the bolts and nuts with spray paint and forget about it. Finding the correct torque on a anti seize application is a futile effort. You do not know the bolt thread specs, crystalize bolt structure, or anything other than the bolt size and thread per inch.

 

[YoshiMoshi]

So how exactly do bolt manufacturers specify a recommended torque when they don't know the desired clamp load for the joint?

Why is not good to use when there's a soft gasket involved if it's not dependent on friction, varied thickness of the joint?

I was thinking the angle method would be an accurate way of ensuring proper clamp load. Once the head of the fastener is flush with the piece and some resistance is given, the amount of rotation to get the clamping force would be the same regardless if the fastener is lubed or dry?

 

[Baluncore]

So how exactly do bolt manufacturers specify a recommended torque when they don't know the desired clamp load for the joint?

They know what any bolt can withstand, before it suffers from plastic deformation. If you do not need most of that torque and clamping force, you are using a bolt that is too heavy and expensive for that job.

Why is not good to use when there's a soft gasket involved if it's not dependent on friction, varied thickness of the joint?

You do not know how much stretch is in the bolt, or how much compression is in the gasket. The compressibility of a soft gasket is hard to specify.

Once the head of the fastener is flush with the piece and some resistance is given, the amount of rotation to get the clamping force would be the same regardless if the fastener is lubed or dry?

Every gasket will have a different thickness and compressibility.
If you reuse a gasket, it will seat differently every time.

You must calibrate the system somehow. The thickness of the clamped joint, gives the length of the bolt. You know the pitch of the thread and the stretch required in the bolt. A soft gasket defeats that method because an unknown amount of the turn angle, goes into compressing the gasket.

Note that: A screw is tightened by turning the head.
A bolt is tightened by turning the nut.
But if you measure stretch by angle, how do you know the bolt head did not turn?

 

[YoshiMoshi]

They know what any bolt can withstand, before it suffers from plastic deformation. If you do not need most of that torque and clamping force, you are using a bolt that is too heavy and expensive for that job.


You do not know how much stretch is in the bolt, or how much compression is in the gasket. The compressibility of a soft gasket is hard to specify.


Every gasket will have a different thickness and compressibility.
If you reuse a gasket, it will seat differently every time.

You must calibrate the system somehow. The thickness of the clamped joint, gives the length of the bolt. You know the pitch of the thread and the stretch required in the bolt. A soft gasket defeats that method because an unknown amount of the turn angle, goes into compressing the gasket.

Note that: A screw is tightened by turning the head.
A bolt is tightened by turning the nut.
But if you measure stretch by angle, how do you know the bolt head did not turn?

Right I would have to hold the nut still while tightening the head of the bolt. Would be a bit difficult to prove that the nut didn't rotate, unless the wrench used to hold was wedged under something very heavy.

It shouldn't be an issue though, where I have a pre-drilled hole into a piece with threads inside of it, right? Not a separate nut.

Thanks for the information on the gaskets.

 

[Baluncore]

It shouldn't be an issue though, where I have a pre-drilled hole into a piece with threads inside of it, right? Not a separate nut.

If the nut was captive, so it could not rotate, then the fastener would be called a screw, and you would tighten it by turning the head of the screw. In that application, it is not a bolt, because you cannot turn the nut to tighten it.

 

[YoshiMoshi]

Thanks for all of the information!

So I'm wondering if using the "angle method" and eyeballing the marks so that they line up is necessarily better than simply taking 10 % or 20 % off the torque specification? Say for example the eyeball angle method puts me off about 5 degrees. How much would being off by 1 degree effect the clamp load? I'm not sure if this can be determined, or if there are to many variables to know?

I'm also wondering, if it would be better to use an angle torque wrench instead of eyeballing it? This would require me to know the angle to fasten the fastener to specification ahead of time. Is there a way to calculate what the desired angle is based on the type of the bolt I'm using, the ideal torque specification from the manufacturer and so on? This might also be to complicated to calculate or to many unknown variables.

I figured I would ask these questions as well.

 

[Flyboy]

Okay, A&P mechanic jumping in here...

I'm gonna suggest that you not bother on torque-sensitive parts, i.e. if they have a torque spec called out. Yeah, they're gonna be rusty and possibly seized, but they call out that spec for a reason. DO NOT MESS WITH IT. If they want an antiseize, then yeah, apply the stuff they call for. Otherwise, you're taking a big risk.

Fun fact... some of the antiseize specs I've seen have been... strange, to say the least. Williams FJ44 turbofans, for example, require you to apply milk of magnesia to the igniter plug threads.

 

[Tom.G]

Williams FJ44 turbofans, for example, require you to apply milk of magnesia to the igniter plug threads.

Probably tighter quality control for a Food Product than for a wrench jockey product.

 

[YoshiMoshi]

I see what you mean, probably best to not mess with anti-seize because of the unknown torque values.

Looking online and doing some additional research. There appears to be a bolt tension gauge devices.
https://www.skidmore-wilhelm.com/collections/bolt-testers
This measures the tension on the bolt.
Essentially you would tighten the bolt down to the torque specification, and used the measure bolt tension.

T = KDP
K = T/(DP)

K is unknown
T is the torque specification from the manufacturer
P is the measured bolt tension with the Skidmore Wilhelm device
D you can measure easily with a micrometer

Now that you know K via calculation, you can look up the K value for the particular anti seize, Loctite, and Anti-Seize technology list it in the technical data. Assuming P is the same from the measured dry value.

T_(Anti-Seize) = K_(Anti_Seize) D_(Measured) P_(Measured_when_dry)

And this give you the torque value when using the anti-seize.

But at $2,000.00 plus for a Skidmore Wihelm bolt tension measuring device, your probably better off just letting it seize up and drilling it out.

 

[YoshiMoshi]

Another option would be a modified turn of nut method using a torque angle adapter.

Essentially this method:

1) Get bolt "snug tight" and mark the bolt in some way so you can return to this starting position.
2) Using a torque wrench with angle adapter, torque bolt to manufacture specified torque value.
3) Write angle down that measured while applying specified torque value.
4) Clean up the threads with a thread chaser, apply anti-seize of your choice.
5) Reassemble the joint getting bolt back to the "snug tight" position and line up the original mark from Step 1.
6) Continue to tighten the bolt to the measured angle from Step 3, using a ratchet with the angle adapter

This would ensure the same amount of bolt tension regardless of the lubricant used? I guess if you wanted to get really fancy, you could measure how many times you go past 360 + anything left over from completely unassembled with the bolt completely out of the nut, to fully assembled to the specified torque value. Then you don't have to worry about the definition of "snug tight" or being off by a few degrees from your marking. Another alternative might be to torque it some predefined low value like 10 ft lb or similar as a starting point.

Thoughts on this method?

 

[gmax137]

Thoughts on this method?

My opinion is you are overthinking this. Just use the appropriate wrench or socket and ratchet and snug the nuts up tight. You don't want it to come loose, but you don't need to go crazy tight.

If you have no experience, you could buy a few nuts and bolts of various sizes; then holding the bolt tight in a vise, use a wrench to tighten the nut until the bolt snaps. Now you know what too much for that size feels like.

 

[Tom.G]

Fun fact... some of the antiseize specs I've seen have been... strange, to say the least. Williams FJ44 turbofans, for example, require you to apply milk of magnesia to the igniter plug threads.

I also seem to have run across that usage as an anti-seize coumpound.

I just spent over a half hour searching for details, etc. Limited success though.
1) There seems to be two versions MgO₃, a 'heavy' and a 'light',

with Milk of Magnesia being a micron-size dispersion of the 'heavy' one​

2) Melting temperature: 990°C, Hardness 4.0 - 4.5 Mohs (rather soft)

Cheers,
Tom