anti seize question

[Michael H.]

Re: anti seize question

Michael -

Dunno for sure - P&A shows they went from the 1-3/8" stud to the 1-3/4" stud in '65.

Thanks John.

I just looked in a 69 printing of the parts book. There were/are three different part numbers for 63-67.

3775683 for 63-64. 7/16-20 x 1 3/8"

3864028 for 65-66. 7/16-20 x 1 3/4"

3910340 for 67-69. 7/16-20 x 1 3/4"

Since the length for 67-69 was the same as 65-66, I have to wonder if the material was changed which may have been the reason the torque was increased from 55-65 to 55-75??

[Joe L.]

Re: anti seize question

Thanks John.

I just looked in a 69 printing of the parts book. There were/are three different part numbers for 63-67.

3775683 for 63-64. 7/16-20 x 1 3/8"

3864028 for 65-66. 7/16-20 x 1 3/4"

3910340 for 67-69. 7/16-20 x 1 3/4"

Since the length for 67-69 was the same as 65-66, I have to wonder if the material was changed which may have been the reason the torque was increased from 55-65 to 55-75??

Michael------

While the length of the threaded portion of the 3864028 and 3910340 are the same, there are other slightly different dimensions between the two parts. For one thing, the head is 1/64" thinner on the 3864028. From what I can find, both studs are GM 300M material grade (SAE grade 8).

[Ronald L.]

Re: anti seize question

One word of caution and I though someone might pick up on it with Michael's post of torque & clamp loads.

The lube can cause a spike in peak torque that can exceed the bolt strength.

That means SNAP CRACK by-by bolt.

I'll give you the scenario:
Chassis bolt+waxed frame parts+air powered torque gun=enough of that wax got on the bolt to lube it and with a fast gun, max torque on the bolt was exceeded.

If you are hand torquing wheel bolts or using an electric gun, chances are you won't exceed the strength limit.

I used a little of that left over from my recent valve job and was very surprised how easily the wheel nuts went on, not galling and leaving fine metal particles.

The idea was not to have thread friction adding into the clamp load.

We'll have to see if someone here has the wheel bolt max yield values before SNAP occurs.

[David A.]

Re: anti seize question

this sounds like a debate for philosophers!
what are acceptable restoration modifications
in the name of safety and or convenience?
iowa

[Michael H.]

Re: anti seize question

Michael------

While the length of the threaded portion of the 3864028 and 3910340 are the same, there are other slightly different dimensions between the two parts. For one thing, the head is 1/64" thinner on the 3864028. From what I can find, both studs are GM 300M material grade (SAE grade 8).

Joe,

I suppose it's possible that increasing the dimension/thickness of the head may have had something to do with increased durability/strength? I can see where over torquing could either snap the threaded portion of the bolt, or pop the head off.

[Michael G.]

Re: anti seize question

Ron, That's not quite what happens with lube, it has nothing to do with tightening speed. I'll explain.

When a wheel nut is tightened, the goal is to stretch the stud slightly. In such a stretched state, the stud becomes a spring, clamping the wheel in place. The trick is to just stretch it enough so that its steel does not permanently deform and/or fracture.

With a wheel stud, this stretching is accomplished by turning the nut: as this turning is done, the thread helix gradually draws the nut onto the stud. Continuing this turning eventually causes the bolt to stretch.

It is very critical to understand that while "Torque" is applied to the nut as it is turned, the measurement of the torque is only a very bad estimate of how far the stud has been stretched by the turning of the nut. For example, if I only measure torque, I can torque two identical appearing stud/nut combinations to 65 ft-lbs and one will be loose, the other will break. The reason for this is that there is one all-determining factor in this:

That factor is friction. Measuring "torque" alone completely fails to comprehend it. Simply put, the friction in the threads and under the head of the nut determine how efficiently the applied "torque" is translated into stud stretch (clamp-load). This means that if we were to make two identical joints, where only the friction in the threads differ between the two, then torque then both to 65 ft-lbs, we would get much, much different results: In the one where very high friction is present, the nut will not be turned as far by the 65 ft-lbs of torque and, therefore, the stud will not be stretched as much, and the clamp-load will be lower.

The bottom line is that adding a lubricant will cause the nut to be drawn further onto the stud, at the same torque, causing the stud to stretch more. This added stretch may be a good thing (added clamp load in the joint) or bad (broken stud). Without a lab test, you can't tell what it did (unless, of course, you end up with several pieces of stud in your hand, then you know right away).

All this is not to say you can't add anti-seize or lubricant, it just says whatever you add shouldn't be much different in friction that what was designed to be there.

[Michael H.]

Re: anti seize question

Ron, That's not quite what happens with lube, it has nothing to do with tightening speed. I'll explain.

as much, and the clamp-load will be lower.

The bottom line is that adding a lubricant will cause the nut to be drawn further onto the stud, at the same torque, causing the bolt to stretch more. This added stretch may be a good thing (added clamp load in the joint) or bad (broken bolt). Without a lab test, you can't tell what it did (unless, of course, you end up with several pieces of stud in your hand, then you know right away).

All this is not to say you can't add anti-seize or lubricant, it just says whatever you add shouldn't be much different in friction that what was designed to be there.

Thanks Michael. I was hoping you would get involved in this discussion.

This was the reason why I posted the formula above, a few days ago. (although I didn't supply the value for friction) There's quite a difference between dry threads and lubed threads.

Many bolt torque specifications from GM also include "Lubed" or "dry" to the spec.

[Ronald L.]

Re: anti seize question

Michael,
Since we could not control the stray presence of the contaminent, we slowed the gun speed to avoid the peak on the torque vs drive time curve and thus avoided snapping the bolts.

[Michael G.]

Re: anti seize question

Ron,

The contaminants altered the coefficient of friction in the joint, making some parts more slippery. In those slippery joints, the fast tool was able to spin some parts more than you expected. That extra spin stretched those bolts too much, fracturing them.

I don't know what kind of tool you were using, but by slowing it down you made the tool more accurate. With the more accurate tool you tightened into a more narrow range, so you didn't have some low-friction parts tightened into the upper limits of the tool's old range. You got the stretch you were looking for, rather than overshooting it and stretching the bolt too much.

[John H.]

Re: anti seize question

Ron,

The contaminants altered the coefficient of friction in the joint, making some parts more slippery. In those slippery joints, the fast tool was able to spin some parts more than you expected. That extra spin stretched those bolts too much, fracturing them.

I don't know what kind of tool you were using, but by slowing it down you made the tool more accurate. With the more accurate tool you tightened into a more narrow range, so you didn't have some low-friction parts tightened into the upper limits of the tool's old range. You got the stretch you were looking for, rather than overshooting it and stretching the bolt too much.

That's why virtually ALL critical torque-control tools in automotive plants, especially multiple-spindle nutrunners in critical applications like lug nuts, cylinder heads, main and rod caps, etc. aren't air tools any more; they're all computer-controlled electric DC motors with both torque and angle control sensors, with precisely-controlled constant spindle rpm during rundown. Every activation of each spindle is computer-monitored and recorded to ensure compliance with specifications.

[Ronald L.]

Re: anti seize question

John, That they are, every single one and we can go back and see who did what when.

[Michael H.]

Re: anti seize question

That's why virtually ALL critical torque-control tools in automotive plants, especially multiple-spindle nutrunners in critical applications like lug nuts, cylinder heads, main and rod caps, etc. aren't air tools any more; they're all computer-controlled electric DC motors with both torque and angle control sensors, with precisely-controlled constant spindle rpm during rundown. Every activation of each spindle is computer-monitored and recorded to ensure compliance with specifications.

Decades ago, we used a completely different method for torquing connecting rod bolts in racing engines. Instead of a specific torque value, the fastener was tightened to a specific amount of bolt stretch.
That way, the lubed/dry condition didn't apply.

I think most/all major engine manufacturers use this method today?

[John H.]

Re: anti seize question

Decades ago, we used a completely different method for torquing connecting rod bolts in racing engines. Instead of a specific torque value, the fastener was tightened to a specific amount of bolt stretch.
That way, the lubed/dry condition didn't apply.

I think most/all major engine manufacturers use this method today?

Rod bolt stretch measurement is still a mainstay in race engine shops, but not in production; DC electric nutrunners and known component properties rule the roost in modern engine plants.

[Michael G.]

Re: anti seize question

Michael,

Its very difficult and expensive to actually measure stretch/clamp-load during tightening, although it is done. As John noted, most control tools utilize some easily measurable dynamic feedback from the tightening process ie: torque, angle, and/or time to estimate stretch and control the tool shut-off.

There are hundreds of different algorithms that use those measurements to estimate where the fastener is in the tightening process, then shut off the tool at the ideal place. Many of those are very successful without the difficultly or expense inherent in actual measurement of stretch.

There are also lot of arguments about where you'd like to end up after tightening, ie: at yield, just beyond yield, 90% of yield, etc.

Most people think of fastening as very simple, it is not, every attachment is just a bit different.

[Michael H.]

Re: anti seize question

Rod bolt stretch measurement is still a mainstay in race engine shops, but not in production; DC electric nutrunners and known component properties rule the roost in modern engine plants.

I thought I read/heard that the streatch method was used on new Z06 engines?
I don't know. I don't follow any of this "new fangled stuff" now.