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Why grease bolt threads?

fishywebfishyweb Posts: 173
edited February 2014 in Road beginners
I see many threads suggesting that grease should be applied to bolts securing stems, seatposts, bottle cages...

What is the function of the grease in these applications? And are there some bolts to which grease should not be applied? Does it make any difference to the torque specified for the bolt?
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Posts

  • petemadocpetemadoc Posts: 2,667
    If you don't then the bolts will corrode and get stuck. Makes no difference to recommended torque
  • BookwyseBookwyse Posts: 245
    Makes no difference to the torque but it does prevent corrosion affecting the bolt and thus making them easier to remove in the future. Even more important around the brakes etc where they are constantly getting sprayed with water.
  • AnonymousAnonymous Posts: 79,692
    Wouldn't anti seize be better than grease?
  • Monty DogMonty Dog Posts: 20,614
    Yes, anti-seize (e.g. Coppaslip) or even better Loctite thread-locker where there is no secondary locking mechanism (lock nut / nyloc) e.g. stem bolts.
    Make mine an Italian, with Campagnolo on the side..
  • lesfirthlesfirth Posts: 1,104
    petemadoc wrote:
    If you don't then the bolts will corrode and get stuck. Makes no difference to recommended torque

    I cant agree.IMHO if threads are dry it can cause excessive friction between the two thread surfaces. If that happens application of the correct torque will not be converted to the desired bolt tension.
  • MattC59MattC59 Posts: 5,433
    edited January 2014
    The torque comments aren't correct.

    If you add a lubricant to a thread it makes it easier to tighten. As a result you need to apply less torque to tighten to a certain point, and thus achieve a certain clamping force. If you apply the recommended torque to a lubricated thread you will be able to tighten it slightly further than you would with a dry thread, perhaps only a turn, but one turn on a 1mm pitch gives you an increased clamping force.

    Obviously the scale of the above effect depends on the bolt size and material, and for a lot of applications, a manufacturer will specify a wet or dry torque value.

    An anti-seize doesn't work in the same way as a grease. It's designed to prevent galling, not purely to lubricate. Anti-seize is far better than grease. Either grease or anti-seize will help an aluminium bolt into a titanium frame (or vice versa) but grease won't necessarily help it out again.

    Thread lock is another beast entirely, it's designed to do exactly what it says, but it won't necessarily prevent corrosion.

    Bottom line, unless you specifically need to lock a thread, use anti-seize, it's not expensive.
    Science adjusts it’s beliefs based on what’s observed.
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  • I take it from this thread that you've never tried to shift a stuck seatpost then! ;)
  • fishywebfishyweb Posts: 173
    Thanks very much all, some very interesting replies.

    One thing worrying me now is whether the increased clamping force obtained with applying recommended torque to a greased bolt could result in damage to a carbon frame e.g. stripping the thread when bolting directly into carbon, or crushing in the case of a stem or seatpost clamp. Thoughts?
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  • The type of torque we are talking about with bike nuts and bolts a bit of copper slip will make negligible difference on the clamping force. Do yourselves a favour and use anti seize grease on exposed areas or areas where dissimilar metals are in contact to help to electrolysis. Free advice from an aircraft engineer
  • MattC59MattC59 Posts: 5,433
    badgermilk wrote:
    The type of torque we are talking about with bike nuts and bolts a bit of copper slip will make negligible difference on the clamping force. Do yourselves a favour and use anti seize grease on exposed areas or areas where dissimilar metals are in contact to help to electrolysis. Free advice from an aircraft engineer

    Absolutely right, Copper Slip won't, but a lube may well. You don't need a great deal of extra clamping force when you're clamping carbon bike components. I know, I split the surface of a seat post because I wasn't paying attention to my torque wench. I only went marginally over the recommended setting :(

    Ps. I'm an engineer too :wink:
    Science adjusts it’s beliefs based on what’s observed.
    Faith is the denial of observation so that Belief can be preserved
  • lesfirthlesfirth Posts: 1,104
    MattC59 wrote:
    The torque comments aren't correct.

    If you add a lubricant to a thread it makes it easier to tighten. As a result you need to apply less torque to tighten to a certain point, and thus achieve a certain clamping force. If you apply the recommended torque to a lubricated thread you will be able to tighten it slightly further than you would with a dry thread, perhaps only a turn, but one turn on a 1mm pitch gives you an increased clamping force.

    Obviously the scale of the above effect depends on the bolt size and material, and for a lot of applications, a manufacturer will specify a wet or dry torque value.

    An anti-seize doesn't work in the same way as a grease. It's designed to prevent galling, not purely to lubricate. Anti-seize is far better than grease. Either grease or anti-seize will help an aluminium bolt into a titanium frame (or vice versa) but grease won't necessarily help it out again.

    Thread lock is another beast entirely, it's designed to do exactly what it says, but it won't necessarily prevent corrosion.

    Bottom line, unless you specifically need to lock a thread, use anti-seize, it's not expensive.

    The second paragraph of the above is total garbage. An extra turn in some circumstances will be catastrophic .

    In my previous post I refered to a" dry thread". The application of grease, anti-seize compound or thread lock will prevent dry threads.

    In general a bit of anti seize is the best, but NEVER EXCEED THE RECOMMENDED TIGHTENING TORQUE.
  • MattC59MattC59 Posts: 5,433
    lesfirth wrote:
    MattC59 wrote:
    The torque comments aren't correct.

    If you add a lubricant to a thread it makes it easier to tighten. As a result you need to apply less torque to tighten to a certain point, and thus achieve a certain clamping force. If you apply the recommended torque to a lubricated thread you will be able to tighten it slightly further than you would with a dry thread, perhaps only a turn, but one turn on a 1mm pitch gives you an increased clamping force.

    Obviously the scale of the above effect depends on the bolt size and material, and for a lot of applications, a manufacturer will specify a wet or dry torque value.

    An anti-seize doesn't work in the same way as a grease. It's designed to prevent galling, not purely to lubricate. Anti-seize is far better than grease. Either grease or anti-seize will help an aluminium bolt into a titanium frame (or vice versa) but grease won't necessarily help it out again.

    Thread lock is another beast entirely, it's designed to do exactly what it says, but it won't necessarily prevent corrosion.

    Bottom line, unless you specifically need to lock a thread, use anti-seize, it's not expensive.

    The second paragraph of the above is total garbage. An extra turn in some circumstances will be catastrophic .

    In my previous post I refered to a" dry thread". The application of grease, anti-seize compound or thread lock will prevent dry threads.

    In general a bit of anti seize is the best, but NEVER EXCEED THE RECOMMENDED TIGHTENING TORQUE.

    Except it isn't. Look it up. And if you really want to rely on it, 30 seconds on Google will help.
    Science adjusts it’s beliefs based on what’s observed.
    Faith is the denial of observation so that Belief can be preserved
  • barrie hbarrie h Posts: 102
    Over torque !
    where I used to work we had air torque guns , all calibrated for dry bolts, if we used bolts with a dried on blue nutlock they would over torque and stretch the bolt through the nutlock melting on the threads and acting like a lubricant
    I know on bikes we dont need high torque but with anti-seize or grease on bolts or nuts its very easy over-torque if you take it to the max.

    Barrie
  • Back when I was doing my post grad engineering training I did a research project into the torquing of bolts for a major engineering company. We found the addition of lubricant to the threads can indeed put extra loading on the bolt for a given tightening torque. Ordinarily this wouldn't be too much of a problem but if you've got a carbon seatpost you might want to be careful.

    Having said that we also found the vast majority of torque wrenches to be quite inaccurate even when they were recently calibrated - this was especially the case at the upper and lower range for the torque wrench. I'd say there's not much chance of getting the correct torque with the tiny values used on bikes anyway.
  • BarteosBarteos Posts: 657
    If the instructions manual mentions greasing the threads (almost all do) it means that recommended torques are for GREASED bolts.
    Applying the same input torque (as read on a wrench's dial) to dry hardware will result in insufficient tension/clamping force due to higher friction.

    Basically torque values without extra info regarding lubrication of the threads are pretty much useless.
  • InitialisedInitialised Posts: 3,047
    Lubricate your bolts (grease, anti-seize, copper-slip whatever) and water cant get in. Don't and it can and will, then if you have a steel bolt in an aluminium frame you've made a battery and the current will slowly cause Al atoms to migrate to the Fe through the water (electrolysis or galvanic corrosion) either weakening the Al structure or just cause the joint to seize and be a pain next time you try and remove the bolt.
    I used to just ride my bike to work but now I find myself going out looking for bigger and bigger hills.
  • mmacavitymmacavity Posts: 781
    http://www.ciclipinarello.com/else/gara ... ISHweb.pdf

    "THREADS, THREAD-LOCKERS, GREASE AND TIGHTENING TORQUES
    One of the most debated issues is the coupling of threaded parts; in particular it is debated if threads should be a) degreased or b) lubricated or c) treated with thread-lockers, and what is the proper torque to be applied in each of these cases.
    In line of principle, we expect threaded couplings to remain stable/tight over time with no loosening, we expect that they can be taken apart when necessary, we expect that they do not generate noises due to micro-movements of the parts, we expect them not to develop corrosion.
    Corrosion, that can be a big problem because it can seize or damage threads, it is frequent between different metals (titanium-aluminum, steel-aluminum). In the past there were no alternatives and grease was used in the threads, to fulfill all four needs. But grease facilitates loosening, does not last forever, migrates, changes characteristics, is washed away, does not always offer sufficient corrosion protection, and reduces noises only temporarily.
    Thread-lockers have been used for many years in mechanics. What is a thread-locker?
    It is a liquid that is applied on the threads during installation and solidifies in the following hours. It is available in many “strengths”, but for the bike it is preferable to use the weak one, Loctite® 222 or Arexons® System 52A22. Thread-lockers offer numerous benefits when used on threaded couplings:
    1) prevent undesired loosening without the need to use high tightening torques,
    2) prevent corrosion in the interface,
    3) prevent any micro-movement with associated noises,
    4) they remain stable over time.
    Thread-lockers solidify when air is absent, therefore the entire space between the threads must be filled with product, otherwise, if not enough product is used, it will remain liquid.
    Using a thread-locker stronger than recommended can seize the threads, especially bigger diameter threads."
  • Monty DogMonty Dog Posts: 20,614
    MattC59 wrote:
    The torque comments aren't correct.

    Thread lock is another beast entirely, it's designed to do exactly what it says, but it won't necessarily prevent corrosion.

    And neither's that one - most Loctite thread lockers are very effective corrosion inhibiters
    Make mine an Italian, with Campagnolo on the side..
  • MattC59MattC59 Posts: 5,433
    Monty Dog wrote:
    MattC59 wrote:
    The torque comments aren't correct.

    Thread lock is another beast entirely, it's designed to do exactly what it says, but it won't necessarily prevent corrosion.

    And neither's that one - most Loctite thread lockers are very effective corrosion inhibiters

    I think that makes my post correct then. :wink:
    Science adjusts it’s beliefs based on what’s observed.
    Faith is the denial of observation so that Belief can be preserved
  • deswellerdesweller Posts: 5,271
    The axial tension generated with a screw is extremely difficult to predict, whether the sliding surfaces are lubricated or not. Having said that, adding lubricant to threads and head faces will not affect the final tension for bicycle applications enough for you to need to worry about it. Your manual torque wrench will not be especially repeatable anyway.

    I speak as someone who has spent many many hours mucking about with various torquing machines in industrial applications. It's a ruddy nightmare, frankly.
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  • lesfirth wrote:
    petemadoc wrote:
    If you don't then the bolts will corrode and get stuck. Makes no difference to recommended torque

    I cant agree.IMHO if threads are dry it can cause excessive friction between the two thread surfaces. If that happens application of the correct torque will not be converted to the desired bolt tension.

    He meant within reason. If the thread is already in good condition then the difference will be marginal. If its clogged up with censored or rust, then this will make a difference.probably
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