Anti-seize and over torquing bolts (1 Viewer)

[LINUS]

I hate that I saw this post so late, I currently work on a car, its trans mount bracket to the trans block bolts require 51 flb torque, the bolts have some kind of rust issue, so I used the rust evop to remove the rust then coat it with anti-seize then I installed it without reducing torque, of course, I did not see it strip the block tread at that time....but I am wondering that:

Should I back to loosen them and re-torque them again with a reduced torque value?
If I just leave it along will these kind of over-torqued bolts damage the trans block thread in the future?

I’m unclear present situation - did you clearly strip the bolt or the threads in the block?

Or did you just hit that ‘starting to yield’ -point & quit there?

If it’s not totally stripped to the point a heli-coil is needed, I’d let it be & unless you get clear signs it stripped more than Jenna Jameson, in that case it’s heli-coil time or new bolt, depending which side stripped.

 

[zhloea]

I’m unclear present situation - did you clearly strip the bolt or the threads in the block?

Or did you just hit that ‘starting to yield’ -point & quit there?

If it’s not totally stripped to the point a heli-coil is needed, I’d let it be & unless you get clear signs it stripped more than Jenna Jameson, in that case it’s heli-coil time or new bolt, depending which side stripped.

thanks for your reply.
I don't think it was stripped.
the situation is that the bolts should be torqued to 51ft/lb "DRY", however after I treated the rust of it and I coat it with anti-seize but I did not reduce the torque and I still torqued it to 51 ft/lb. there are 2 of these kinds of bolts that go to the trans block (transmission mount bolts), based on the talking we should reduce the torque in this case.
I am worried that if these 2 bolts should be considered as over-torqued? If so, how serious it would be then should I do something about it?
(I am worrying particularly because they go to the trans block and are hard to access, need remove a lot of things...)

 

[BILT4ME]

thanks for your reply.
I don't think it was stripped.
the situation is that the bolts should be torqued to 51ft/lb "DRY", however after I treated the rust of it and I coat it with anti-seize but I did not reduce the torque and I still torqued it to 51 ft/lb. there are 2 of these kinds of bolts that go to the trans block (transmission mount bolts), based on the talking we should reduce the torque in this case.
I am worried that if these 2 bolts should be considered as over-torqued? If so, how serious it would be then should I do something about it?
(I am worrying particularly because they go to the trans block and are hard to access, need remove a lot of things...)

If it didn't strip, leave it alone.

Over-torquing stretches the threads and repeating it over and over can fatigue the material of the bolt or mating threads.

While it can be more than the design, there is a "service factor" allowed in most of these. Using anti-seize can cause them to be over-torqued by 30%, but it may still be within range. If it didn't already strip, I would not re-do it.

 

[saline]

This is well known by engine rebuilders.

 

[sunrk]

Some fasteners cannot be assembled with anti-sieze because they have a specific yield function or some other critical role. Head bolts and flywheel/driveplate bolts are the ones that come to mind. Head bolts are lightly lubed with oil. Flywheel bolts are threadlocked.

Anywhere the threadlocker is specified probably means anti-sieze can't be used.

With most other fasteners not performing mission-critical roles using anti-sieze is fine but you need to reduce the torque setting by at least 1/4 (30 percent is generally the recommendation) to achieve the same factory torque spec in the actual thread cavity or nut.

It's very important with stainless 304 or 316 grade fasteners when replacing old rusted normal steel ones in any non-critical application to use anti-sieze as they are more prone to thread galling, but some non-critical applications don't suit using stainless fasteners either. Seat mounts for example - they should be 8.8 hi tensile but still can be assembled with anti-sieze.

 

[saline]

Full disclosure before I begin. . . I work for Loctite.

There are two main points in this thread. Regarding the original point of removability, there is only one reason bolts that are properly installed become difficult to remove later on and that is rust. I know it's hard for most people to believe, but in a typical threaded assembly, there is only about 15% metal to metal contact. (flights of the male thread touching flights of the female thread) The other 85% is air. Air which contains water and different amounts of salt depending on where you live. This is why we get bolts that are rusted shut.

Anti seize is primarily intended to prevent galling the threads as you install the fastener, especially with stainless steel parts. It is, as stated several places above, a lubricant. This keeps the male and female threads from welding themselves together (seizing) as you install. Secondarily, it remains in the threads thus preventing water from entering the threads, thus preventing rusting the threads together later on. The problem with anti seize is, that it always stays a lubricant. A lubricated bolt can more easily loosen both when you want it too and when you don't. The whole point of a torque specification is to apply a certain clamp load. You want that clamp load to stay constant until you're ready to disassemble the part.

There is a way to prevent water from entering the threads without leaving a lubricant behind. Using a medium strength threadlocker does lubricate the assembly process but it chemically changes into a hard plastic when it cures. Now you have a hard plastic filling up that 85% space. This does two things for you. It prevents unwanted loosening and also prevents rusting. So a thread locker is also an anti seize in the sense that it will take the same amount of torque to remove that fastener tomorrow as it will 10 years from now. Remember that the medium strength (blue) Loctite is removable with the same hand tools you installed with. However, if you're concerned about rounding over the heads of smaller bolts and screws, you can use the low strength (purple) Loctite. Same rust preventing benefits with lower removal torque needed.

Now, about the second topic. Torque vs clamp load for lubricated vs dry fasteners. FJ4068 is absolutely correct. It's too complicated to explain so I'll sum it up.

Torque is related to clamp load via a factor called "K"
The impossible part is that the "K" factor for any threaded assembly depends on the following:
1. diameter of the bolt
2. pitch of the flights
3. engagement of the flights
4. metallurgy of the male threads
5. metallurgy of the female threads
6. friction coefficient of the two metals describe above working against each other
7. quality of the fastener (i.e. how consistent are all the above from one end of the fastener to the other)
8. which particular lubricant? (by name and number)

So there's no way to tell you how much you should reduce A torque on A bolt. Believe me, engineers ask me that all the time.
However, if you're planning to put 30 or 40 thousand of the same nuts and bolts together and you can send me a couple hundred for testing, that's another story. That's how Toyota, and everybody else, comes up with the torque specs in the FSM.

So if I'm such an expert. . . how much do I reduce the FSM spec torque? "just a bit"

Here are my 2 cents on this issue. The best way to present torques is to give a dry torque (no lubricant) below the dry tensile strength of the bolt, then provide a degree of rotation beyond that.
What is important when "torquing" is to get the proper tension on the bolt. Enough to achieve a seal, but not enough to snap it. Torque is a rotational force that just indicates a rational resistance. So, a torque will be different for dry verses wet torquing, clean vs rusty. Wet leads to a reduced friction, therefore more rotation, therefore more axial displacement of the pitch of the screw, resulting in higher tensile force in the bolt. This because the threads slip easier. Think of it like a ramp. You can push a weight higher on a greased ramp. This gives you more vertical travel, which in a bolt results in a longer stretch putting it closer to snapping. That is why I think adding torque to a lubricated mating is wrong.
Now, more torque creates higher friction making the association of torque to tensile strength higher. The torque and angle method reduces the error. The pitch of the thread, therefore rotational position, provides the tensile strength, not torque. In this method you stop torquing it where the friction starts becoming a major factor in torque readings. Then the rotational angle gives you a precise tensile displacement. This makes it less reliant on the condition of the mating surfaces.

Interested in any feedback.