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Check the torque on your wheels or else..........................

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Torques are normally specified without the use grease. If the bolts are then greased, the reduction in friction would result in increased tensile stress within the bolt itself, possibly beyond the elastic limit.

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3 hours ago, Lutz said:

Torques are normally specified without the use grease. If the bolts are then greased, the reduction in friction would result in increased tensile stress within the bolt itself, possibly beyond the elastic limit.

They are also specified on new, clean threads and seats, add a bit of corrosion to the mix and the tensile stress in the bolt would be reduced.

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We also but put a bit of copperslip in the center flange, however even the young lads knew not to get any on the studs or near the stud holes.

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4 hours ago, JTQ said:

 

The "need" is because here in this application, the wheels have been known to come loose, even after an initial re-tightening. I accept is is a pity it is so, and it should not be so, but it "is" if you want to have a better chance of retaining the wheel.

Why should there be any risk whatsoever of stretching the bolts [here they are not using studs], providing you use the correct tightening torque and do so without lubricating the threads?  Note that the quoted torque in the manual is a "dry value" not a lubricated value.

 

Lubricating threads  is indeed  a technique for achieving more accurate and repeatable bolt tension, but to use the same value tightening torque specified for doing a "dry" assembly, when they are lubricated, is very bad practice with every chance of yielding the bolts.

 If you lubricate threads and then torque them up to the "dry" value, then the achieved bolt tension will be at least 10% higher than the designer intended, and depending on the products used could be considerably higher.

 

 

It is a widespread misunderstanding amongst mechanics, not correctly trained in the subject, that use of lubricants here is good practice, where the reality is that here it is an exceedingly poor practice, for the reason given, the bolt tension resulting is too high.  

 

In more precision application, we as designers do sometimes specify the use of lubricants and quote the appropriate torque for the lubricated assembly. But there we also specify the lubricant, or bolt surface treatment, and will be quoting the lower torque value that requires.

 

However, here Al-Ko are specifying, a "dry torque value", so thread lubrication must not be used, as it introduces other real dangers.

Lubricating centring rings or spigots presents no such issue as they form no part of the wheel retention design, and can be prone to corrosion, so the right lubricant can mitigate that issue. However, Al-KO in their caravan chassis ranges don't use centring rings anyway.

Well presented. and accurate post.  :goodpost:

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