Copper Grease

[tanuie]

Hi, Am I right in thinking you shouldn't put copper grease on wheel bolts.

 

[DSM10000]

From an engineering purist stance I believe that a grease or other substance applied to a thread will not allow for an entirely correct torque reading.

As to if this matters in real life..................... ,well I have applied copper grease to wheel bolts for some years and have not had a wheel fall off or noticeably loosen.

Do you use a torque wrench when tightening your wheel bolts?

 

[MancMike]

Whenever I've torqued down my wheel nuts on any car (using a torque wrench), I always feel that I'm coming up against friction on the threads, rather than a tension against the wheel hub. So I've applied a slither of CG to remove that friction. It gives me another half turn probably before I get to the specified torque. I'm no engineer, just my experience.

I've never had a nut come loose through using it. They've always still been at torque when removing them months later. (If I try to tighten before loosening, to test, I get a click straight away, so they've not come loose)...

 

[Giantvanman]

As above. Have used a very thin smear on wheel bolts and nuts on every car, regardless of size, as well as on hub face when alloy wheels are fitted. No loosening, no contamination.

 

[DSM10000]

As above. Have used a very thin smear on wheel bolts and nuts on every car, regardless of size, as well as on hub face when alloy wheels are fitted. No loosening, no contamination.

Good point re hub, I forgot to add that

 

[moonloops]

Grease = change in clamping force so a no no from me. If manufacturers don't spec it for grease then bad idea to do so IMHO ....

 

[BlackC55]

No, never. If the threads are clean there is no point putting anything on there, If the threads are poor then there is something wrong.

 

[MancMike]

Grease = change in clamping force so a no no from me. If manufacturers don't spec it for grease then bad idea to do so IMHO ....

^ I can't argue with that logic.

 

[tanuie]

From an engineering purist stance I believe that a grease or other substance applied to a thread will not allow for an entirely correct torque reading.

As to if this matters in real life..................... ,well I have applied copper grease to wheel bolts for some years and have not had a wheel fall off or noticeably loosen.

Do you use a torque wrench when tightening your wheel bolts?

Hi yes I do use a torque wrench to tighten the wheel bolts, the reason I ask is I have had a wheel come off and I put copper grease on the bolt threads so I was wondering if this is the right thing to do. I believe the torque settings for a CLK is 110nm.
Many Thanks.
PS I do put the copper grease on the face of the hub.

 

[ivandraganov]

The torque wrench is the culprit,no problem puting a little grease.tighten wheel bolts by hand with the original wrench supplied.I had loose bolts after using the torque wrench.perhaps should by set at 150nm.but I would not use it again

 

[Doodle]

I generally reserve copper grease for the little bolts. The ones that inevitably rust and seize otherwise, and then shear off. However, they're usually not holding on anything important, and so the tightening torque isn't an issue.

If you're going to use a torque wrench, make sure it's accurate, otherwise it's next to useless (and quite possibly the cause of ivan's issues above).

 

[Giantvanman]

I thought a little look around the internet might be of use and I found this discussion interesting (worth going through all the posts) Should you really grease parts you want tight? - BentRider Online Forums (I can assure everyone I have no affiliations with that forum). And then there is this one which seems to go either way http://www.honestjohn.co.uk/forum/post/index.htm?t=82119

I must admit, my use of copperslip/grease on threads is based on the teachings of some old and very old engineers, of which there were several in the family.

 

[nb_racing]

Grease = change in clamping force so a no no from me. If manufacturers don't spec it for grease then bad idea to do so IMHO ....

Agree. We actually do tests of this sort of thing at work and moonloops is correct.

 

[Giantvanman]

Agree. We actually do tests of this sort of thing at work and moonloops is correct.

Are you able to elaborate? I have read several arguments about bolt stretch, friction, etc etc. The scientific reason against doing so would be interesting.

 

[hotrodder]

The important bit with bolts is the installed tension... very basically (and ignoring 'stretch bolts') they need to be tightened until they just begin to stretch which results in an easily reversable interference fit of the threads. Metals bend and stretch in two ways, elastically and permantly. The former occurs over a very small range and when the force is removed the piece returns to origional dimensions. Then when the yield point is reached they stay stretched/bent although a small amount of 'springback' occurs which is due to the smallish window of elastic behaviour

Installed tension is difficult to measure but can be calculated from torque values with one caveat... a large portion of the torque applied when tightening a fastener is due to friction which means that the state of the threads makes a massive difference to the actual installed tension for a given torque value- clean and dry versus manky/crud in the threads versus lubrication

There's a generic torque chart here that provides values for both dry and lubed threads (different K factors)... http://www.spirol.co.uk/library/sub_catalogs/cmpl-Torque_Specifications_us.pdf
M12 x 1.5 class 10.9 is fairly typical of many wheel bolts and the torque figure for MBs with this size of wheel bolt is typically 110Nm.
The torque values given in the link are 131.5Nm dry (k factor of 0.2) or 98.6Nm lubed (k factor of 0.15).
Many manufacturers of anti seize and other thread lubricants publish k factors for their products as the type of lubricant makes a difference for example http://www.henkel.mx/mxe/content_data/83749_LT3355v4_MROantiseize.pdf

Then there's lubricating the face of the hub itself which is a common one for people that have encountered wheels that had corroded to it... the wheel bolts themselves are only supposed to clamp the wheel tightly to the hub and the joint is then supposed to function kinda like a clutch i.e. it's the friction between the mating surfaces that deals with torque from acceleration, braking etc. If the driving forces were taken by the bolts they'd be subjected to bending and shear loads which isn't ideal. This is also one of the reasons behind hubcentric wheel mounting i.e. the hub has a piloting diameter which locates the wheel concentrically leaving the bolts to act purely in tension

 

[rorf]

If your climate is wet and salty in summer and wet and salty in winter I would definitely put CS or oil on wheel nuts/bolts. I live in a dry climate and have always used CS and torque to 110Nm

 

[MancMike]

That all makes perfect sense. I probably won't grease any more. I hadn't thought of the hub being greased then putting the twisty force on the bolts, rather than the hub/wheel interface.

 

[nb_racing]

Are you able to elaborate? I have read several arguments about bolt stretch, friction, etc etc. The scientific reason against doing so would be interesting.

The torque relies on the surface friction on the thread of the bolt; thread to thread, metal to metal.
If you apply a lubricant to this contact area you lose the surface friction.

 

[Giantvanman]

The torque relies on the surface friction on the thread of the bolt; thread to thread, metal to metal.
If you apply a lubricant to this contact area you lose the surface friction.

Edit: My follow up question made no sense.

 

[camerafodder]

The torque relies on the surface friction on the thread of the bolt; thread to thread, metal to metal.
If you apply a lubricant to this contact area you lose the surface friction.

The surface area of the contact points between the bolt head and the wheel is also a component of the torque required.