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Theory behind cutting torque spec in half when using anti-seeze

BruceB83

NAXJA Forum User
Location
Dacula, Georgia
Can somebody explain why you should cut the torque spec of a bolt in half when you use anti-seeze on the threads? Also, how much anti-seeze is recommended when you do cut the torque in half? Usually, I put on one swipe of the brush down the entire length of the bolt.

I understand it acts as a lubricant but does it really reduce friction enough to where torque can be reduced by half? I have I hard time trusting roughly 45 ft/lbs on my lug nuts with anti-seeze!
 
Where did you hear that?


I always use anti-seize on my lugs, I figure they need it to compensate for the wear and tear of me removing the lug nuts so damn often. I don't cut back on the torque, but I only use a dab of anti-seize.

Like you, no way I'd go with 45 ft lbs.
 
i always heard that you cut the torque down by a third. 100lbs/ft would be 66ft/lbs.

this has come up before an 5-90 gave an explaination
 
there's some variation of opinion on how much to reduce torque values
The "preload" of dry threads causes the torque value to be somewhat false.
I've seen several different figures. 2/3 to 1/2 reduction of dry thread torque values.

You really want to see preload, get some dirt in the threads, the friction will bind them up before the nut/bolt even seats down. Or poorly machined threads, with lots of irregularities.

Anyways, the main reason antiseize merits a reduction in torque, is it almost eliminates any friction/preload in the threads. So nearly all of the torque is translated into tension in the bolt or stud. So you will see more stretch.

That's why all torque values are stated dry. They have the friction of dry threads added in.
 
Where did you hear that?


I always use anti-seize on my lugs, I figure they need it to compensate for the wear and tear of me removing the lug nuts so damn often. I don't cut back on the torque, but I only use a dab of anti-seize.

Like you, no way I'd go with 45 ft lbs.

I ran across it several times when looking for searching for some torque specs.

i always heard that you cut the torque down by a third. 100lbs/ft would be 66ft/lbs.

this has come up before an 5-90 gave an explaination

A third seems a little more reasonable to me, but who am I to argue with science. I've seen a few of his responses to it.

I guess where I'm confused is what is truly the proper way to torque bolts when anti-seize is applied? I mean, you never hear of people breaking off bolts when torquing bolts with AS on them...ya know?

I know I'm over analyzing this...I have to do it every once in a while...:spin1:
 
FWIW, the Permatex website (http://www.permatex.com/documents/tds/Automotive/81343.pdf) has this to say:

http://www.permatex.com/documents/tds/Automotive/81343.pdf said:
DIRECTIONS FOR USE
1. Clean mating surfaces before application
2. For best results, apply to clean, dry surfaces.
3. Clean surfaces with PermatexÒ Brake & Parts Cleaner.
4. Wire brush any loose surface rust.
5. Apply Anti Seize to the parts that require protection.
6. Reassemble parts using normal torque values.
7. Wipe off excess material.
8. Clean brush on aerosol product to make future
applications easier.
 
I was gonna say ..
I've always used antisieze with the original torque spec too.

Torque spec does change with moly thread lubes or oiled threads, though.
 
I work in aviation, and we do have different torque values for dry bolts and lubed bolts. However, the torque value stays the same as "dry" when using anti-sieze compounds, which jibes with the Permatex info.
 
As stated (and as I've covered before,) the reason for the change in torque is due to the lubricity of the anti-seize. It's not that you're likely to rupture the screw - however, I have seen cases of threads being pulled out of castings for torquing to full "clean, dry" spec with lubricated threads.

If they now have never-seez that doesn't change torque values, I may have to switch (then reprogramme my head.) Fortunately, I don't often use never-seez on screw threads - mainly on slip-fit assemblies that don't slip apart very well when you need them to (TRE tapers, manual shift shafts for the NSS, ...) I've also used it when the "clean, dry" torque spec exceeds what any of my torque wrenches are capable of measuring, and it's worked well.

Another advantage to lubricating the threads is that you actually get more consistent tensile preloading through mitigating friction.

As far as how much to change for what lubricant? It varies by lubricant, and I've given the old thumb rules here several times before. It's rare that I will install a screw dry - although the "wetting agent" is most often either threadlocker, RTV (for screws that get wet with water, and I can't secure a replacement that won't corrode,) or sometimes PTFE paste (typically when specified - RTV doesn't change torque specs. PTFE paste = -10%.)
 
I think this is why the "torque to turn" method was created. Basically in situations where precise torque measurements were needed the variance in thread friction was too much so the specs "15 ft lbs + 90 degrees" with shoulders and threads of bolts oiled is used. Not my words, just what was taught to me in H-D tech school. Sound logical?
 
I think this is why the "torque to turn" method was created. Basically in situations where precise torque measurements were needed the variance in thread friction was too much so the specs "15 ft lbs + 90 degrees" with shoulders and threads of bolts oiled is used. Not my words, just what was taught to me in H-D tech school. Sound logical?

It's also called "torque angle," where you turn to a predetermined (and lower than normal) torque value and then an additional angle - typically 60-180*. It's finding more use on automotive cylinder head screws of late...
 
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