Sealing the bolt thread from corrosion

[SEBASTIANOFA]

Hello, Is there a thread sealant that allows to seal the metal from corrosion and keep the tightening torque ​​unaltered? I have to use torque-to-yield bolts, for a car subframe and engine mount, this bolts are designed to stretch during the torquing.
I think about threadlocker, grease, silicone but they are all liquid and I guess they reduce the friction in the threads changing the torque specs

 

[TugboatEng]

Most automotive manufacturers use Loctite 242 or equivalent for sealing chassis bolts. Loctite 222 is another option with lower retention.

Loctite 290 would be the perfect match for the requirements you have provided as it can be applied after installation.

TTY, however, eliminates the problems associated with friction as you're tightening to an angle and not a torque. Galling should be of concern for TTY bolts as they have more degree of rotation under high stress than conventional torquing. Automotive fasteners come with a lubricating coating pre-applied to prevent galling.

 

[SEBASTIANOFA]

the problem is that the other part of the thread is not seen, it is inside the chassis and therefore I cannot use the piercing model.

does the air that remains trapped between the various grooves of the thread cause corrosion?

I think the best is to completely cover the thread with something but I’m not sure if the torque values will change

 

[TugboatEng]

Threads are close fitting and have a capillary action that can draw moisture in.

If you specify a specific sealant you can adjust your torque procedure to work with that sealant. However, with TTY, this should be unnecessary. The fastener itself sets the clamp load regardless of friction.

Have you considered using capped nuts? There are a few options including weld and adhesive mount nuts.

 

[SEBASTIANOFA]

Could you explain to me why TTYs don't suffer from this problem? my intent was to use weak Loctite threadlocker, I don't need to glue the parts, just isolate them from moisture. However, I do not know if there is a better sealant that modifies the friction less. So do you think I can use a threadlocker or an anti-seize agent while maintaining the tightening torques indicated in the workshop manual? I got the bolts new and original but unlike the first factory ones, these are gray, perhaps galvanized and do not have that green coating that the factory ones have.

 

[TugboatEng]

With TTY, you're shooting for a window of elongation. It's quite wide. Once you reach yield, even as you advance the bolt further the torque doesn't change. The goal of TTY is to land the fastener anywhere on the flat part of the stress/strain curve. It requires much less precision than conventional torquing.

 

[SEBASTIANOFA]

Thanks, so basically, the 100 (or 60) nm are to set the bolt but the 1/4 of turn make the plastic deformation that is range is wide enough to can use or not a threadlocker in it, if I got it right.
Exactly?

 

[TugboatEng]

Yes and you should feel it in your wrench as it will no longer take increasing force to rotate the bolt further.

 

[Tyler S Sims]

You could use Dri-Loc fasteners from Loctite, which have pre-applied thread sealant.

https://www.henkel-adhesives.com/us...adhesives/pre-applied-adhesives-sealants.html

There are also bonded seal washers that prevent fluid ingress with an elastomer seal on the washer itself.