Loctite works mostly like a glue. Theres different strengths of them. For example the blue medium strength loctite 243 when used correct typically requires a breakaway force of 14-34N after 24h cure time (per its manual).

So if you tighten a preloctied screw to 6N and wait for the loctite to harden you'd expect anything from 14-34N depending on the materials to undo the effect of the loctite. Now I'm no physicist so I can't tell you if the 6N of the initial bolting will add to the 14-34N resulting in a breakaway force of 20-40N. It is of no consequence however. 14-34N is plenty for the bolts used on bicycles. I have broken the heads of several torx screws in speedplay pedal spindles because they used to have ample amount of loctite.

Screwing around with loctied screws will of course interrupt the bond that loctite creates. So basically this is a stupid idea. The idea of loctite is so you can leave it alone really because it won't come undone by itself no matter what you do (assuming correct application).

And you have come across just one reason I don't worry about using a torque wrench on bikes. That being, you don't have any information regarding how the joint was designed and how fasteners were to be preloaded. State of lubrication is the biggest factor in the torque preload relation. Given the same torque, high friction creates lower preload. Also, is it running or total torque? Do you have a click wrench or a dial wrench?

Yes Loctite does alter the amount of preload you get. It will lower it generally but also make for a wider spread of values. I have seen torque tension data (this was for spacecraft using typical tools, quality control, and processes for that type of hardware) on small fasteners that used Loctite. It was not pretty with a mean preload much lower than one would traditionally estimate for even dry installed fasteners and a variance of like +/- 50% from the mean, whereas with lubed fasteners you may expect 10-15% variance and dry 25-÷35%.

If you are interested, look at Appendix B in NASA-STD-5020, which has some discussion on Loctite and other liquid locking compounds. The document is freely accessible online.

For the other poster talking about breakaway force, it is torque, not force. Yes it helps with that. Loctite will serve its function of minimizing self-loosening, but it doesn't magically increase preload. The poster is mixing units. N, a force unit, is not the same as Nm, a moment or torque unit. As Loctite dries it affects Nm, not N.

While your reply surely does answer a lot of questions that weren't asked or even related to the OP's actual question I'm sure you have your reasons for doing so. With regards to your wise-ass comments concerning my scientifically incorrect usage of torque and force I have used the term breakaway force because that is the lingo used in loctite documents. I have this on hand from a loctite description document:

"Properties
•Viscosity: medium, liquid
•Breakaway force for M10 bolts: 26 Nm
•Proven tolerance to light contamination by industrial oils
•Prevents bolts and nuts loosening as a consequence of vibration"

I'm sure this is incorrect if you say so, but I'm not trying to write a paper here so I'll stick with what the manufacturer says and what is helpful with regards to the OPs question.

Tigermilk is spot on, but I am not sure the original question was answered.

Lubed or loctited on the bolts will have a lower torque value than dry bolts.

Fastenal has a nice little calculator.

https://www.fastenal.com/en/83/torque-calculator

Problem with that calculator is it gives no indication of it the values are total torque or effective torque (total minus running). Loctite can be problematic with excessive running torque, and again, if you are working with a click wrench, you are completely guessing at what the fastener is actually seeing. You really need a dial wrench if you want a better answer.

That's very useful, thanks!

You can call it breakaway force, breakaway torque, a biscuit, or a grasshopper. I don't really care as long as the units are correct. But you said


You are using units of force. The end user may not fully understand what you are trying to convey. Words matter, but more importantly units matter to a greater degree if you have somewhat confusing words. Using "force" and "N" is not prudent. Comments were not intended to be wise-ass at all. Merely clarifying so nobody gets bad information.

Agreed, but we aren't talking about aircraft that are being put together with DC torque tools.

Torque = D (nominal diameter) ( function of the bolt geometry ) x F (clamping force ) x K (coefficient of friction)

Applying loctite to the threads will reduce the coefficient of friction in the above.

If you apply the same Torque to the same size bolt in the same joint with loctite applied to the threads the clamping force will increase. if the torque was specified for ‘dry’ threads you can get increased clamping forces, that lead to failure. If the torque specified was for lubricanted threads loctite should not be an issue. You have to know with torque values , was it specified for dry or lubricated threads.

torque is the mechanism to get clamping force. You don’t want torque per say, you want clamping force.

Joints become loose basically for two reasons, the nut or bolt turns ( vibration ) or stress release (thru cold flow of the materials in the joint or different rates of thermal expansion for joints that see temperature variations.

If vibration is an issue loctite can be useful in preventing nut or bolt rotation. It will do nothing for stress release.

Are bolt torques usually specified as wet or dry? As an aside, I also use loctite as an anti-seize.

Generally if nothing is specified it is assumed to be dry.

Some bolts as you’ve probably seen have dry loctite patches pre-installed on them from the manufacture of the widget you are installing. That torque value should have taken into account that loctite patch.

In general adding lubricant to threads and torquing to a specified value that was for dry threads will lead to joint failure. You will get a clamping force in excess of the design parameters. To much is not always a good thing, You want baby bear not momma or papa bear.

Exactly, when applied wet the Loctite acts like a lubricant, just as grease will. This will increase the clamping force needed to get to a desired torque.

The "Glue" factor of Loctite, which increases the torque needed to remove, does not affect the clamping force at all.

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