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Old 02-03-2013, 12:25 PM   #21 (permalink)
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Well I need to rotate them soon so I will pick up anti seize and put some on when I do, that was my original thought but I wanted to know if anyone else does that.
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Old 02-04-2013, 12:32 PM   #22 (permalink)
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On the last page of this thread, and numerous times before, the question of lubed vs dry threads has come up, and I’ve seen lots of opinions rendered. As a member of ASM, The Materials Information Society, I thought I’d get you a proper engineering answer to the lubricated threads issue.

I read thru several sources, but thought this one summarized the issue best in terms that most people could understand. If you really want to see the raw text, formulas and tables, I’ll try and copy sections (the file is copy protected), or you can just accept my summary & commentary. From the definitive Handbook of Bolts and Bolted Joints, edited by Bickford/Nassar, with the chapter on the use of Thread Lubricants (and why the wrong choice can screw the pooch…) written by Novak/Patel of the Fel-Pro Chemical Company.

The assembly torque of a fastener is consumed by two mechanisms: friction-free bolt stretching and overcoming friction. A portion of the applied torque on the bolt head stretches the bolt. The balance of the bolt torque overcomes thread friction and under-head (nut to wheel in this case…) friction.

General assembly practices call for the use of thread lubricants. A thread lubricant fills the spaces between contact points, thereby reducing the metal-to-metal contact and prevents galling and seizing. In effect, it acts like a microscopic ball bearing to keep surfaces separated for easy assembly/disassembly. Thread lubricants have widely varying “nut factor”, K, (coefficient of friction), and choosing the correct one for the application is extremely important. Dependencies include thread pitch, surface area & metal coatings, application to thread and/or under head region, evaporation opportunity, amount applied, etc.

The efficiency formula indicates how much of the applied torque is being used to stretch the bolt, and how much is used to overcome friction. The use of lubricants can yield an efficiency of up to 100%, and all of the torque is used to stretch the bolt. Conversely, it also serves to reduce the torque required to remove the bolt, as friction is not in play. Gasket leakage (in this case wheel damage), fastener overload, fastener loosening, and fastener fatigue failures can occur if the proper preload is not developed at initial assembly.


So that’s what the book says. My take on it is that if the manufacturer says “clean and dry threads”, then they empirically determined a torque spec that gives up a substantial amount of total torque to tread and head friction, but also uses that friction and metallic galling to keep the lug nuts in place. If they wanted you to use a lubricant, they would have:

a) Specified exactly what lubricant to use, which surfaces, and how much to apply.
b) Reduced the torque spec (considerably?) to account for near zero friction, and to protect the fastener system and the aluminum wheel.
c) Provided some kind of locking mechanism to ensure that the assembly does not self-loosen.
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Old 02-04-2013, 01:30 PM   #23 (permalink)
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I have to say haven tightened a heluva lotta lug nuts over the years, by hand, with an air impact, with an electric impact, the threads having been wet, dry, greased, oiled, what have you, I have never had a stud snap or a nut come loose, so I have to view all of this with a bit of a lopsided grin. The tolerable range of torque/stud stretch is so wide I think you really have to be ham-fisted or completely inexperienced to get it wrong, almost no matter what.

Of course the first step on the path to lug-nut perdition is for inexperienced hands to use a torque wrench on anything other than clean, neatly-groomed rust-free dirt-free water-free oil-free threads (and similar for under the nut).

The second step is when someone oils or greases under the nut- I think that's the only real no-no.
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Old 02-04-2013, 06:14 PM   #24 (permalink)
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To get an idea of whether this is really a big deal or not, I went for some real numbers and came up with this:

Example: You want to tighten an AN6 bolt (3/8”-24) to 75% of the bolt’s 'proof' strength. That’s considered a normal working parameter, according to Fastenal. Proof strength is the point where normal elastic deformation transitions to plastic deformation. The bolt doesn’t break, but it begins to permanently stretch and is no longer offering the same kind of holding power because it begins to ‘taffy pull’.

A cadmium plated and dry bolt would require 28.9 lb-ft to achieve this.

A moly anti-seize treated bolt would only require 19.9 lb-ft to get to the same clamping force!

So what happens if you go the full 28.9 lb-ft? You now apply 45% greater torque, which exceeds the bolt’s proof strength and stretches it. It still might not break (you are a little below the 'yield' strength), but it is permanently deformed.

If you torque lug nuts to 72 and use anti-seize, you might be getting closer to 100 lb-ft. Not an issue to you on your lug nuts? How about your disk brakes?

How about the head bolt on that EJ25 engine? Would choosing the right lubricant (or none at all) matter there? If you are serious about working on cars, I think this stuff's important.
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Old 02-04-2013, 07:07 PM   #25 (permalink)
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Obviously when working on someone's car and they were the type to oil or use anti-seize on the threads, you'd have to reduce the torque.

That's a large reason why I do not think it's not often appropriate to use a torque wrench on lug nuts, there is almost no rational way to translate the torque when operating under real-world conditions.
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Old 02-04-2013, 07:49 PM   #26 (permalink)
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When a car comes in my shop with anti-seize, I clean the lug bolt. The aluminum the nut is made of will resist seizure, especially if you are rotating your tires regular. I also change out my wheel nuts every 2 years. They will stretch/deform long before the bolts.

Wal Mart is the worst one for putting anti-seize on a lug bolt and the top for breaking bolts or cross threading the nut onto the bolt.
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Old 02-04-2013, 08:35 PM   #27 (permalink)
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Where have you run into aluminum lug nuts?
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Old 02-05-2013, 07:58 AM   #28 (permalink)
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The lug nuts on your car are aluminum/nickel alloy. There are other wheel nuts manufactured using other metals, but aluminum alloys are used for reduced weight and manufacture cost. If you want extra strength and light weight, you could even get titanium lug nuts.
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Old 02-05-2013, 08:14 AM   #29 (permalink)
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I didn't know that, Cardoc. I always assumed it was steel on steel for the bolt/nut. Thanks!
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Old 02-05-2013, 08:16 AM   #30 (permalink)
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OK, last piece of evidence on this matter for the non-believers. In all shop manuals we see torque values. In reality, torque values mean absolutely nothing unless you understand the conditions by which they were obtained. What the engineering team is looking for is clamping force. In the case of a lug nut, they may specify 10,000 pounds. You achieve a clamping force by stretching the bolt, and it’s the tension that the stretched bolt produces that holds the system together. How does one measure bolt elongation in the field? You can’t!

So instead they come up with a relative measurement technique that you can reproduce with basic tools – how much torque it takes to produce that amount of elastic deformation. The torque value is only valid for this system. Change any parameter, and the results could be way off. In the system they specify a certain diameter and thread pitch, dry plated threads and conical nut surface in contact with a dry aluminum wheel. With these parameters, it might take 70 lb-ft to achieve 10k lbs. Lube it, and the value might drop to 50 lb-ft. Ignore this and torque to 70 lb-ft, you might now have a clamping force of 14,000 pounds. And as I explained yesterday, doing this 40% overstress may very well exceed the bolt’s proof rating, resulting in permanent elongation.

And if you are thinking, well, I’ll just undertorque from now on, also remember that the lub reduces vibration induced loosening resistance. I wouldn’t want to be the guy who has to tell the jury I undertorqued because I thought it was a good idea.

Still don’t believe me? Download this handy chart from Spaenaur.
http://www.spaenaur.com/pdf/sectionD/D48.pdf

And a minor comment about the chart – they used K values of 0.2 dry, 0.15 lubed. That’s probably for a basic machine oil. Anti-seize can be as low as 0.11, so the dry-lubed delta could be considerably worse than what’s shown here.
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