What?? Where did this info come from?

In my experience, you want to use cutting oil on smaller threads even if not absolutely required because you'd want to use the lubrication to be able to determine when the tap is cutting and when the tap is bottomed out and about to break, or jamming up with swarf and about to break, which is easy to do because M6 taps aren't very strong.

Anti-seize can change the installed bolt tension greatly, the increased lubricity can lead to an over-torqued fastener, or bolt breakage. IIRC the rule of thumb is to lower the torque wrench setting something like 50% vs. bolt installed dry. Oil has a similar but lesser effect.

Lubricating Threads

Sorry, but that is not remotely correct. To assure you obtain the correct torque settings, and the targeted clamping force, the fasteners (including washers) should be lubricated. This is particularly important in torque to yield applications like the flywheel bolts. Optimal repeatable results can be obtained using something like ARP's Ultra Torque compound, but in cases of dissimilar metals where later corrosion and thread galling is likely to occur, an anti seize compound should be used. When using a lubricant, no change in the torque wrench settings should be used, just apply the recommended torque.

If you want to see more information on the subject, check out ARP's website, they have an extensive white paper on what actually happens to the resulting torque (and clamping force) repeatability with and without lubrication, with vastly more data then you will probably ever need.

Bolting is what I do for a living and if there is a torque value, it has been calculated using a lubricant. In fact there are so few non-lubricant applications it's not worth mentioning.

The lube used will change the applied torque because some are more slippery than others. Oil slippery but not in a good way for bolts vs. moly, very slippery and good for bolting. For the car, a standard anti-sieze is good. For special applications the lube would be chosen taking into account many different aspects of the use.

In a typical industrial application, 90% of your turning force is used to overcome friction, so a change in lube can have a big effect on the residual load. The residual load or clamping force, or elongation is what engineering is interested in.

Standard practice, at least in automotive assembly, is NOT to lubricate threads and or washers. In specific applications, lubricant may be called out, but those are the anomaly. ARP might claim to lubricant "ALL" threads because in their world of specialty high strength fasteners, this is the standard they can expect from the users of the product since they have a specific attention to that detail. But I'd wager that you wouldn't find a single lubricant near any fastener in an automotive assembly plant.

A specified level of torque applied to a fastener head will result in more clamping force when the fastener is lubricated than when it is not lubricated. The reason is because you are reducing the friction between the thread flanks and thereby increasing the tension in the bolt. Hence, if you lubricate the threads and apply the specified torque value, you run the risk of breaking the bolt or the mating parts since you are applying a greater clamping load than intended. Bolted connection design takes into account all these factors and the design engineers follow proprietary tables when they size a bolt for an application, which for the most part, is a dry fastener that has a reducing clamping load than the same fastener when lubricated.

VW/Audi/Porsche flywheel bolts have a thread locking compound that will not work properly if you lubricate the threads with oil.

I don't know what the hell ARP is talking about, and I don't have time to read it, because I own a Boxster which is waiting for me in the garage.

You would lose your wager. First of all, engines and transmissions are not assembled in the same plant the car is, they are shipped in from a facility the is setup specifically to assemble them, and they do use specialized lubricants on the fasteners. I've watched them do it. Secondly, the torque spec to reach the design clamping force is set with lubricated fasteners because dry fasteners will reach that torque spec level due to friction in the treads and at the bolt head before actually achieving the desired clamping load level, leaving the parts with less clamping load than expected.

You really ought to take the time to read the ARP paper, you might actually learn something.

Exactly............

JFP! A 1 word agreement. Must be a first around here. Thanks for the agreement.

Dry friction cannot be calculated or predicted. Just the oil from your hands will change the residual loads during testing. In fact a used (but not damaged) fastener will have better consistency than a new fastener due to burnishing and the effect of "virgin" fasteners. It gets very complicated depending on application.

Not entirely true. There have been plants that house both engine assembly and vehicle assembly under the same roof. Except in this context we're not talking about assembling engines, we're talking about some random M6 bolt that goes into a caliper. So my comment was regarding vehicle assembly, not engine assembly. Even still, only rotating assembly bolts are lubricated within an engine at assembly. Bolts that hold on accessories like the starter and alternator are not.

I understand how bolting friction works, since that's exactly what I explained in my previous post, and what you explained as well. But if you're saying that a torque specification like those in a service manual require lubrication on thread to achieve that spec, I think that is where our opinions differ.

The designers for a vehicle understand what clamping force they are looking for, and to achieve that force they will specify a dry torque... which is much higher than a lubricated torque to overcome that friction, but still achieves the same clamping load in the end. I'm sure they do base it on a lubricated torque at some point, but the torque value you will see is for a dry fastener.

Why dry? Because when they're building the vehicle, lubrication on assembly lines is a) messy, b) an added expense, and c) from a torque calibration perspective, lubrication is an additional control point that can cause process variation since lubrication amounts, lubrication type, and even location on the fastener are hard to keep consistent. Way too many variables to control.

It is much easier to specify a dry fastener torque since the characteristics of a dry fastener are much much much more consistent and well established in proprietary design standards.

You are correct on one point: We disagree.

I agree. In the 21 yrs that I worked in the Mass Transit industry we never used anti-seize on a torqued fastener that required a specific torque. But,all these fasteners were brand new .In this case a heli-coiled wanked out hole? I be putting a whole lot of locktite not anti.

I work as a process engineer in automotive assembly and part of my responsibility it is to work off of primary vehicle drawings created by vehicle designers to set up precision assembly tooling. I suppose my experience in bolting cars together isn't correct either. :)

Anyway, no disrespect meant to JFP, just friendly discussion. Let's agree to disagree.

The ARP info is interesting as JFP asserts. I used it for all the many ARP bolts on my M96 rebuild.

Here is the ARP link - you'll see what I mean perhaps:
http://www.jegs.com/PDFs/ARPAssemblyLube.pdf
An example, if the manufacturer did the original spec based on the factory taped hole, he would have known exactly what the conditions in the hole were and wrote a spec accordingly -probably with dry thread resistance/friction in mind . On a used car, the threads may have been chased, badly re-cut,dirty,oily,have coolant ,grease,threadlock or whatever there. So how do you write a spec for that ? A competent mechanic (like JFP) uses experience and skill to find a reliable solution.The specifying engineer(if it was me) would decline to give a torque spec for the used car because I could never know what the friction was.Tell me the friction and the material and fastener type & size and yes, it is easy to give a torque range. With the M96 the limiting factor will usually be the ductility of the alloy of the block.
Geeks read more here:
http://www.designnotes.com/companion/manual-1.html


When I rebuilt my M96 I chased and cleaned all the threaded holes .In as many as possible I used custom length s/s studs in the engine(+red Loctite) and green for the s/s nuts. There will never be a problem there ! Corrosion is a risk that compels the use of some type of lubricant/sealant/locker regardless of the torque specs. The exhaust header bolts are a good example. Yes, mine are s/s !

We're talking about two different applications, I agree that critical fasteners are always specified with OIL, or specially formulated lubrication like ultra-torque. We were discussing "generic" body fasteners, which all torque charts list as "clean and dry" threads. As compared to that specification, oil will slightly lessen the required torque, but anti-sieze has a fairly large effect. Notice on the attached chart the the torque with A/S is reduced by 1/3. Once you start talking about old or damaged/corroded fasteners, it's hard to arrive at accurate torque values, there's just too many variables.
http://www.alliedsystems.com/pdf/Wagner/Forms/80/80-1057.pdf