WDB124066
MB Enthusiast
- Joined
- Apr 17, 2009
- Messages
- 6,176
- Car
- 1996 E320 Sportline Cabriolet x 2
I make a lot of money out of this so I find it better than most things...
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Not really my type of coating but I would go and always have gone, clean and dry threads on road wheels. Greasing the threads attracts grit and moisture which itself could cause binding. Correctly torqued dry bolts have never given me any issues.
http://www.honestjohn.co.uk/forum/post/index.htm?t=82119
From the link above:
'...Incidentally, the joint face between the wheel and hub should also remain dry - this face is, effectively, a clutch face transmitting drive and braking torque between the hub and wheel. This torque should be transmitted by the friction, and not by shearing the bolts...
...a greased contact at this interface *can* result in slippage under extreme loading, which will load the bolts in shear and bending which they are not designed for.'
...so no copper grease on the hub face either, it would seem.
markjay said:From the link above:
'...Incidentally, the joint face between the wheel and hub should also remain dry - this face is, effectively, a clutch face transmitting drive and braking torque between the hub and wheel. This torque should be transmitted by the friction, and not by shearing the bolts....
Lots of reference to 'copper grease'. Is CS actually a grease with the same lubricating properties as true grease or is it an anti-seize compound with much less lubrication?
I don't know so am asking the question of those that might. If it's not a true grease and it's lubricating coefficient is less then maybe it's use on wheel bolt threads are not quite the devil as claimed.
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
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
hotrodder said: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
It doesnt make sense,otherwise as soon as the bolts are loose, they will shear off strait away wich isnt the case.And reducing the torque on slightly lubricated thread is wrong.the most of the grease is squeesed out of the threads anyway..
.And reducing the torque on slightly lubricated thread is wrong.
If that were true, engines wouldn't need oil.most of the grease is squeesed out of the threads anyway..
Me? I'm confused.. I was refering to why ivandraganov thinks the principle of the clamp loading is wrong.As per your post #73. Over torquing threads is not good practice, especially older worn ones...
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