bolt torque settings and anti-seize

[Chris H.]

I will be removing and re installing the exhaust manifold on my 396. I was considering using anti-seize on the mounting bolts when re-installing the manifold. Is this recommended and how will it affect the torque readings when using the torque wrench?

Thanks, Chris

[Dale Pearman]

Re: bolt torque settings and anti-seize

I use anti-seize in this application and published torque specs as well. Just be sure to use french locks. The anti-seize won't harden-up like 30 weight oil and over time the cap screws will loosen. As far as torque is concerned I feel there's little difference between the "slipperiness" of 30 weight and anti-seize.

Varooom!

[grr]

Re: bolt torque settings and anti-seize

Chris, go buy a tube of Fel-Pro or equal high temp anti-seize lubricant. I've used it on boiler furnaces door studs and superheated steam line joint attachments for years. Just go to the web and look for Fel-Pro and give them your zip code with an e-mail and they will tell you where it is for sale in your area. It won't effect your toque setting either.grr#33570

[Chris H.]

Re: bolt torque settings and anti-seize

I guess more specifically my question is, will anti - seize or any lubricant on the threads create artificialy low readings on the torque wrench due to the thread lubrication?

[grr]

Re: bolt torque settings and anti-seize

Chris, like I said I don't think it has anything to do with your torque settings especially on a car. Maybe something that has to be just exact at certain temperatures for expansion/contraction/atmospherics but nothing that technical about a car. Maybe someone else can find reasoning but I've used it on lots of hi-temp fasteners and never found any problems especially when taking back apart.I have on hand some Permatex anti-seize lubricant which prevents corrosion,ease of disassembly,won't wash away,elinates galling-seizing,lubricates and withstands up to 1600 degrees F (870c). It's just like Fel-Pro's C-5 hi-temp anti-seize. You can pick up at any auto zone etc. grr#33570

[Jeff Gunn #29146]

Re: bolt torque settings and anti-seize

Using any type of thread lubricant, whether it is anti-seize or 30 weight oil, does have an impact on torque readings on the wrench. If you have lubricated threads the torque will read lower than unlubricated threads because there is less friction between the fastener and the tapped hole. While working offshore we used charts when torquing fasteners which showed required torques for unlubricated threads versus threads lubricated with two or three different lubricants. Typically each type of lubricant had a slightly different torque value. In the case of your Corvette it is probably more important that you be consistent on your torques rather than hitting some specific value "dead nuts". The published torque value _probably_ assumes some type of lubricant, so use those values and be sure to torque all the fasteners equally and you shouldn't have any problems. Jeff


Jeff's '74 Corvette Restoration Project

[grr]

Re: bolt torque settings and anti-seize

Jeff, thanks you made my point. The torque specs you mentioned are for special applications due to manufactures requirements to warrant the machinery etc. So when it blows or fails they can send out their team of technicians to make sure all the safety trips and alarms are working for insurance reasons. You know , mecghanical or human error. As per mfr: specs. I totally follow you. As for our cars, I agree with that also. We aren't working on multi-million dollar pieces of machinery. Thanks for the post for Chris's question.grr#33570.

[Jeff Gunn #29146]

Re: A little more explanation

I should have gone into a little more detail, perhaps. The reason that you must torque all the bolts evenly is that the bolt with the least amount of preload will be most subject to loosening due to vibration, etc. If they are all evenly torqued there is no "loosest" fastener and the component is much less likely to require retorquing in the future. As an example, for those of us who have installed headers, there is always at least one bolt that you can't quite get the right grip on to fully tighten. Did you ever notice that that particular bolt is ALWAYS the loosest again when you go to retighten a few days/weeks/months later? There's a reason for that. So again I will reiterate that you should torque to the manufacturer's spec, but pay particular attention to evenly torquing all fasteners with respect to one another. Jeff


Jeff's '74 Corvette Restoration Project

[WayneC]

Re: bolt torque settings and anti-seize

Many years ago when I was a co-op college engineering student, I did a series of tests on this very subject in a laboratory environment at the direction of my employer. Unfortunately my memory has long ago faded on the exact results, but I seem to recall that the effect of lubricants on the proper torque setting was considerable.

If I recall correctly, a special "washer" with stress gauges attached was used to determine how much "squeeze" force was being applied by sample bolts as they were tightened on a block of appropriate thickness, with and without thread lubricants; torque was graphically plotted against force. Later, samples of the same bolts were subjected to increasing stretching force on a machine to plot bolt length versus force and determine the point at which the bolt began to fail.

The purpose of the torque spec is to get the bolt tensioned to a point that it begins to stretch, but well below where it will begin to fail (by taking on a permanent change in length).... thus if it is over-torqued it may begin to fail.

If I use a generous amount of anti-sieze on a bolt, I usually reduce the torque spec by at least 10 to 20%. It might be worth contacting a bolt manufacturer to see if they have any words of wisdom.

[WayneC]

Re: bolt torque settings and anti-seize

A quick web search yielded this url for a chart of torque specs for bolts with 2 different lubricants (no dry specs, though):

http://www.centuryperformance.com/fasten3.htm

Here is some verbiage on the subject of bolt torque that I found at another website which would seem to indicate that a simple method of obtaining accurate torque might be to torque a dry fastener down while counting bolt-head revolutions from a "snugged" low-torque starting position, then remove it, lube it, and re-install it using the same low starting torque and number of revolutions:

>>>>>> "Torque Application:

Because your torque wrench alone can't consistently predict clamping force we will need to combine techniques. For the most accurate results a combination of torque measurement and "Turn of the Nut" methods must be used. The "Turn of the Nut" or "Torque-Turn" method figures the amount of clamping force applied by a single rotation of the fastener without regard to friction. The basic principal is that after a certain snug level (or threshold) has been reached, every turn of the nut applies a set amount of tension to the joint.

This method provides an easy way to spot defects and assure proper clamping force for the highest quality joint. For example, if the desired torque is reached but the number of rotations is low the threads may be damaged, or the fastener may be bottoming out in a under-tapped hole. If the desired torque has not been reached but the number of rotations exceeds the optimum it is likely the threads have been stripped. When the applied torque and the number of rotations are both within the desired range you have a quality joint.

So when you have to torque a critical assembly, be sure to have the factory call out the specs for torque and degrees of rotation past snug".

[Chris H.]

Re: bolt torque settings and anti-seize

Very interesting. Thanks for all the info everyone.

[Bill Bradley]

Re: bolt torque settings and anti-seize

Society of Automotive Engineers (SAE) publishes technical specifications for a variety of things automotive related including proper methods of determining torque specs for different grades of fasteners used for automotive applications. I don't have a direct reference for you but a little searching will provide the reference. To the best of my knowledge, all torque specs are specified with lubricated threads.

[Dale Pearman]

Spark Plug Torque

I once knew a hobby Corvette dude that used a torque wrench on everything, even spark plugs!. He got so wound up with torque compensation as a function of lubricant that he started, (don't do this at home) scientifically analyzing torque compensation as a function of the length of the socket wrench extention! After a while this anal champ got treated to a few shock treatments at the local nut house and now he's feeling MUCH better!

Varooom