Copper grease - or not?

[Mave]

CrutyRammers said:

witko999 said:

Mave said:

steveo3002 said:

thebraketester said:

I always use aluminium anti sieze on my wheel bolts and mating faces.

and have they ever fell off?

id say someone keen enough to use something is also wise enough to tighten the wheel nuts properly

You can tighten the wheel nuts to the spec torque, but if you lubricate the joint faces then the joint isnt loaded in the way it was intended. Those mating surfaces are intended to take ~90% of the torque. If you lubricate them, the bolts end up taking the torque in bending instead. Personally I make sure the threads and joint surfaces are clean and take the wheels off twice a year for servicing.

How on Earth is lubing a thread and/or cone introducing a bending moment?

He's talking about the mating surfaces, is he not?
Less friction on those surfaces = they move in sheer = the bolts will take a bending force.

Yep. Highlighted for clarity.

Edited by Mave on Friday 24th September 10:13

[Megaflow]

Mave said:

CrutyRammers said:

witko999 said:

Mave said:

steveo3002 said:

thebraketester said:

I always use aluminium anti sieze on my wheel bolts and mating faces.

and have they ever fell off?

id say someone keen enough to use something is also wise enough to tighten the wheel nuts properly

You can tighten the wheel nuts to the spec torque, but if you lubricate the joint faces then the joint isnt loaded in the way it was intended. Those mating surfaces are intended to take ~90% of the torque. If you lubricate them, the bolts end up taking the torque in bending instead. Personally I make sure the threads and joint surfaces are clean and take the wheels off twice a year for servicing.

How on Earth is lubing a thread and/or cone introducing a bending moment?

He's talking about the mating surfaces, is he not?
Less friction on those surfaces = they move in sheer = the bolts will take a bending force.

Yep. Highlighted for clarity.

Edited by Mave on Friday 24th September 10:13

The joint face between the wheel and hub should always be clean & dry for that reason. A little copper slip on the register diameter of the hub to ensure it doesn’t seize on is all there should be.

[witko999]

You're talking about the hub face of the wheel slipping against the hub. Fair enough and I now understand your point, but unless you've carried out some testing on whether the hub face is slipping, dry vs. lubed, I remain dubious.

[witko999]

Should be pretty easy to calculate actually

[105.4]

Haltamer said:

I usually save it for the hubs / wheel backs to prevent any sticking, even though I have them off at least once a month for some kind of tinkering

For me, all of the above plus the shoulders of the studs.

[Mave]

witko999 said:

You're talking about the hub face of the wheel slipping against the hub. Fair enough and I now understand your point, but unless you've carried out some testing on whether the hub face is slipping, dry vs. lubed, I remain dubious.

Have a look at the charts in this link - you can see how the load transfers from hub face to bolt as the clamp load reduces, which is directly analogous to what happens if the friction coefficient reduces.

https://link.springer.com/article/10.1007/s11668-0...

Edited by Mave on Friday 24th September 12:07

[witko999]

Thanks for the link. I see the effect you mention, although it is unclear to what extent that copper grease would reduce the friction.

I would still put copper grease on the threads though, along with periodic checking of nut torque, which should probably be done anyway.

[CrutyRammers]

Krikkit said:

thebraketester said:

How much force is required to bend or shear four/five M14 bolts?

About 60kN each, i.e. 600kg.

The reason it doesn't matter that much what we do with wheel nuts and mounting faces (including way over-torquing them with a big impact at your local tyre fitter) is they're way, way over-specced to build in huge tolerance to abuse and fatigue.

Quite. One of the cases where it's cheap and simple to build in massive safety margins, to protect everyone from themselves.

[voram]

It's madness to grease things that aren't supposed to be greased.

If you're worried about things getting stuck just develop a routine of loosening and retightening once a year. You don't even need to take the wheel off. Loosen all the nuts a few turns then move the car a few feet and apply the brakes firmly. Jack wheels one at a time and retighten.

[witko999]

voram said:

It's madness to grease things that aren't supposed to be greased.

If you're worried about things getting stuck just develop a routine of loosening and retightening once a year. You don't even need to take the wheel off. Loosen all the nuts a few turns then move the car a few feet and apply the brakes firmly. Jack wheels one at a time and retighten.

You've obviously never worked on an old car. Copper grease is often the difference between something that comes apart, and something that shears in half.

[Mave]

CrutyRammers said:

Krikkit said:

thebraketester said:

How much force is required to bend or shear four/five M14 bolts?

About 60kN each, i.e. 600kg.

The reason it doesn't matter that much what we do with wheel nuts and mounting faces (including way over-torquing them with a big impact at your local tyre fitter) is they're way, way over-specced to build in huge tolerance to abuse and fatigue.

Quite. One of the cases where it's cheap and simple to build in massive safety margins, to protect everyone from themselves.

I don't think the margins are that massive. I'd need to look up some bolt tables but it wouldn't surprise me if, say, 100Nm takes you surprisingly close to the proof stress. I think you've got a few 10s of percent margin, not x 10 (or even x2!) margin. If you allow the bolt to take some bending as well, then you also need to take fatigue into consideration.

Edited by Mave on Friday 24th September 13:10

[Mave]

witko999 said:

You've obviously never worked on an old car. Copper grease is often the difference between something that comes apart, and something that shears in half.

For service joints like wheel bolts, i don't think the age of the car comes into it.

[witko999]

Well, obviously I wasn't suggesting I've been snapping wheel studs!

[CrutyRammers]

Mave said:

CrutyRammers said:

Krikkit said:

thebraketester said:

How much force is required to bend or shear four/five M14 bolts?

About 60kN each, i.e. 600kg.

The reason it doesn't matter that much what we do with wheel nuts and mounting faces (including way over-torquing them with a big impact at your local tyre fitter) is they're way, way over-specced to build in huge tolerance to abuse and fatigue.

Quite. One of the cases where it's cheap and simple to build in massive safety margins, to protect everyone from themselves.

I don't think the margins are that massive. I'd need to look up some bolt tables but it wouldn't surprise me if, say, 100Nm takes you surprisingly close to the proof stress. I think you've got a few 10s of percent margin, not x 10 (or even x2!) margin. If you allow the bolt to take some bending as well, then you also need to take fatigue into consideration.

Edited by Mave on Friday 24th September 13:10

Don't shatter my faith in engineers
I'll defer to your obviously superior knowledge here.

[brman]

Krikkit said:

thebraketester said:

How much force is required to bend or shear four/five M14 bolts?

About 60kN each, i.e. 600kg.

The reason it doesn't matter that much what we do with wheel nuts and mounting faces (including way over-torquing them with a big impact at your local tyre fitter) is they're way, way over-specced to build in huge tolerance to abuse and fatigue.

That is not the point on greasing mating faces though.
It is not the load or even the bending of the bolts causing fatigue failure that is the main issue. Not in my experience anyway. It is that wiggling a bolt back and forwards is very likely to loosen that bolt off. As soon as it is slightly loose the movement becomes much greater and it then loosens off rapidly. Then you end up (as I did, twice!) with a wheel wobbling around in a slightly scarey way.

.

[Mave]

CrutyRammers said:

Mave said:

CrutyRammers said:

Krikkit said:

thebraketester said:

How much force is required to bend or shear four/five M14 bolts?

About 60kN each, i.e. 600kg.

The reason it doesn't matter that much what we do with wheel nuts and mounting faces (including way over-torquing them with a big impact at your local tyre fitter) is they're way, way over-specced to build in huge tolerance to abuse and fatigue.

Quite. One of the cases where it's cheap and simple to build in massive safety margins, to protect everyone from themselves.

I don't think the margins are that massive. I'd need to look up some bolt tables but it wouldn't surprise me if, say, 100Nm takes you surprisingly close to the proof stress. I think you've got a few 10s of percent margin, not x 10 (or even x2!) margin. If you allow the bolt to take some bending as well, then you also need to take fatigue into consideration.

Don't shatter my faith in engineers
I'll defer to your obviously superior knowledge here.

It's not about deferring to knowledge, it's about discussing information.

I just took a look at a bolt calculator for grade 8 M14 bolts - You've got a yield strength of approx 64kN.

94Nm with a dry thread puts 50kN into the bolt (so only about 30% margin!!)
With lubrication, you get that same 50kN with only 80Nm (so applying 94Nm would take the bolt load up to ~58 kN) - not a massive margin IMHO

[Krikkit]

brman said:

Krikkit said:

thebraketester said:

How much force is required to bend or shear four/five M14 bolts?

About 60kN each, i.e. 600kg.

The reason it doesn't matter that much what we do with wheel nuts and mounting faces (including way over-torquing them with a big impact at your local tyre fitter) is they're way, way over-specced to build in huge tolerance to abuse and fatigue.

That is not the point on greasing mating faces though.
It is not the load or even the bending of the bolts causing fatigue failure that is the main issue. Not in my experience anyway. It is that wiggling a bolt back and forwards is very likely to loosen that bolt off. As soon as it is slightly loose the movement becomes much greater and it then loosens off rapidly. Then you end up (as I did, twice!) with a wheel wobbling around in a slightly scary way.

Yes as soon as it's free to move everything happens very quickly. Not really the point that was being made of course.

Mave said:

It's not about deferring to knowledge, it's about discussing information.

I just took a look at a bolt calculator for grade 8 M14 bolts - You've got a yield strength of approx 64kN.

94Nm with a dry thread puts 50kN into the bolt (so only about 30% margin!!)
With lubrication, you get that same 50kN with only 80Nm (so applying 94Nm would take the bolt load up to ~58 kN) - not a massive margin IMHO

So the monkeys at tyre fitters with their impact guns are going way, way over the yield strength? Why don't we see failures?

[Mave]

Krikkit said:

brman said:

Krikkit said:

thebraketester said:

How much force is required to bend or shear four/five M14 bolts?

About 60kN each, i.e. 600kg.

The reason it doesn't matter that much what we do with wheel nuts and mounting faces (including way over-torquing them with a big impact at your local tyre fitter) is they're way, way over-specced to build in huge tolerance to abuse and fatigue.

That is not the point on greasing mating faces though.
It is not the load or even the bending of the bolts causing fatigue failure that is the main issue. Not in my experience anyway. It is that wiggling a bolt back and forwards is very likely to loosen that bolt off. As soon as it is slightly loose the movement becomes much greater and it then loosens off rapidly. Then you end up (as I did, twice!) with a wheel wobbling around in a slightly scary way.

Yes as soon as it's free to move everything happens very quickly. Not really the point that was being made of course.

Mave said:

It's not about deferring to knowledge, it's about discussing information.

I just took a look at a bolt calculator for grade 8 M14 bolts - You've got a yield strength of approx 64kN.

94Nm with a dry thread puts 50kN into the bolt (so only about 30% margin!!)
With lubrication, you get that same 50kN with only 80Nm (so applying 94Nm would take the bolt load up to ~58 kN) - not a massive margin IMHO

So the monkeys at tyre fitters with their impact guns are going way, way over the yield strength? Why don't we see failures?

In my opinion it's probably because 1) they don't clean the threads so they're seeing more friction than expected, and 2) the bolt spec is for minimum properties and most bolts are above minimum properties.

Why do you think we don't see failures?

[brman]

Krikkit said:

Yes as soon as it's free to move everything happens very quickly. Not really the point that was being made of course.

Yes, sorry,perhaps I should not have quoted your post, that comment was more aimed at the implication that a bit of bending of the bolts was not a problem.

Krikkit said:

So the monkeys at tyre fitters with their impact guns are going way, way over the yield strength? Why don't we see failures?

I would guess that is because the bolts (when over stretched) stretch rather than fail. So actually most people will not notice. I have seen this on my E91 recently. A tyre place overtightened the bolts to the extent I needed a breaker bar to undo them. They looked ok but I ran them into the hub without the wheel in place and found that, just at the point they would normally be tight (as shown the the witness marks on the threads) the bolts jammed. On further inspection it became obvious the bolts had stretched at that point, increasing the thread pitch. With the wheel in place you could not tell as the wheel appeared secure at the point the bolts jammed.
How many times you could do that before total failure I don't know and am not about to try to find out.

[GreenV8S]

Mave said:

I just took a look at a bolt calculator for grade 8 M14 bolts - You've got a yield strength of approx 64kN.

94Nm with a dry thread puts 50kN into the bolt (so only about 30% margin!!)
With lubrication, you get that same 50kN with only 80Nm (so applying 94Nm would take the bolt load up to ~58 kN) - not a massive margin IMHO

It is quite scary how close that takes the bolt to its nominal yield point. Maybe these bolts routinely exceed the spec, but you really wouldn't want to count on that.