offshorebear

Dumb question, but I am new to biking. When people talk about "greasing" threaded fasteners, do they really mean anti seize just so that they don't get stuck?

A cursory look at ASTM standards doesn't define anything for thread lubrication other than power transmission screws, but there is a whole lot about anti seize on threaded fasteners.

Duragrouch

You would have to ask that, darnit. I salute your due diligence. I looked for corroboration and see conflicting statements:

Statement from Permatex (tm) anti-seize lubricant Technical Data Sheet: "Reassemble parts using normal torque values."
https://441py33rout1ptjxn2lupv31-wpe.../tds/80078.pdf

Statement from Anti-Seize Technology (tm): "Reduce the torque values by 25% for lubricated fasteners."
https://www.antiseize.com/PDFs/torqu...ifications.pdf

So....
1) My earlier statement that fastener torque values are designed for clean, dry threads with new surface finish, still applies.
2) After lubricating with an anti-seize lubricant, not certain. It was my understanding that the fine (soft) metal particles in anti-seize compounds negates the lubricant effect, but this may be wrong, the metal particles my only be there to act as an anti-seize barrier if the grease carrier burns off or is otherwise removed.
3) Lubricating threads with standard grease or oil definitely changes the torque/tension relationship.

308jerry

I can't believe it, not one person mechanic, engineer or novice have brought up Torque To Yield. Basicly all bolts are springs. If they're over tightened, they stretch and will eventually break. . Under tightened and there isn't enough clamping force.

Bikesplendor

I really appreciate your contributions to the thread. If you come up with anything else, please feel free to post whatever you find. Thanks.

Duragrouch

I will research this. I am guessing you mean, what is a bolt torque-to-yield value, and stay below that, not torque to it. But off the top of my head:
- The bolt yield value will change, not only with bolt size, but thread pitch, and bolt grade.
- Most bolts used on bikes have a higher yield strength than the material they are threading into. Grade 2 bolts are 57KSI, grade 5 are 92KSI, grade 8 are 130KSI. 4130 steel frame tubing is 63KSI. What this means is that the frame threads may strip before the bolt yields, especially with one or two diameters thread length. And even more likely with an aluminum frame (which is why in my past professional life, some aluminum parts came from the factory with Helicoiled threaded holes). Some ultra-high-strength frame materials, like Reynolds 953, have very high ultimate tensile strength (255-290KSI) so the yield strength is probably way up there too, possibly in excess of the bolt strength, but I don't see exact numbers right now.
- Bolts with shoulder shafts at the minor thread diameter (nuts will slip over shaft) instead of major diameter, like cylinder head bolts, and casing bolts for wankel engines, have much greater elastic stretch, and as such will accommodate greater changes such as temperature. They are also much less likely to break at the threads due to stress concentration.

EDIT: From wiki:
I stand corrected. In my career as an engineer, I never ran across TTY fasters. Though I did encounter Huck Bolts that are pre-stretched when mounted, then a nut crimped around the threads, so rotational friction during torquing is not a factor.

bakerjw

I have been taught that when you grease threads and contact surfaces, you get much more accurate torque compliance.
For lug nuts, I always use antisieze which normally is powdered aluminum in grease.
For bicycles, I use copper based antisieze.

308jerry

We've used the TTY fasteners for quite a few years now, mostly in engine applications. On the headbolts and rod and main bearing caps. You can only use them one time and throw them away after that. You lube the threads, torque to a very low value, then depending upon the application turn them a specific angle, 90/180 degrees. It claims that the torque value is closer across the board with this process and actually eliminates the lubed or unlubed delema.

Duragrouch

Eliminates dilemma in terms of any torque change vs tensile load for the fastener, I agree. But the main purpose of anti-seize is to.... keep the bolt from seizing due to galling or corrosion. But there should be no problem with lubing those bolts, in fact probably needed even more due to higher tensile load.

Correct me if wrong, but looking online, TTY bolts typically have an undercut unthreaded shank to yield there. Thus, I don't think TTY bolts can be used where there is not space for a long unthreaded shank between the head and threads.