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I have the habit of lubricating most screws on a bike with whatever grease I have laying around, except those which aren't meant to be tightened completely, there I use threadlocker (for example the screw holding the brake lever on a canti brake lever set because it would make it compress to the point the lever gets squeezed and can't proerly be pulled anymore). I put some grease on the thread and sometimes on the bottom of the bolt head as well. Also other parts which might move/need loosening (e.g. inside of stem, seat clamp, seat post, cranks, ...) get some greasy treatment. I do this since I've had major problems in the past loosening screws and parts of all kinds, especially drivetrain related, presumable because when not greased water can get in and form rust etc making the two threads stick together. Or maybe different types of material tend to form a bond, not sure. And because in my head I have the idea that when there's less friction one can actually tighten a screw better. And because I assume it can avoid creaking sounds.

Does this make sense? (bonus question: I mostly use generic ball bearing grease for everything, would there be something more appropriate for things which get fastened?). I don't recall ever having problems with things coming loose due to this practice, but are there any screws or parts which should definitely not be lubricated and why?

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  • If you have a square-taper bottom bracket, I would not recommending greasing the bolt that holds the cranks. This is typically mentioned in the leaflet coming with such a bottom bracket. – Christian Lindig Aug 5 '17 at 13:21
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    @ChristianLindig on the other hand my crank bolts came pre-greased from the factory for a square taper crank (they were clipped into the holes in the cranks, which were filled with grease) – Chris H Aug 5 '17 at 14:26
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    Steel does form a bond with aluminum, so it's a good practice to get into. When a torque is specified, they should really tell you what sort of grease if any, because it can make a big difference. But of course that information is rarely given. – Chris H Aug 5 '17 at 14:27
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    @ChristianLindig It's the norm for manufacturers to not recommend greasing the taper, but greasing the bolts is a pretty universal practice. Stuck crank bolts are no fun. Usually I also grease the bolt shoulder, as Shimano has you do by pre-greasing that area on new cranks with four little dots of grease, to make sure the thread preload is what I want it to be. – Nathan Knutson Aug 6 '17 at 3:32
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Basically every metal-in-metal thread on a bike should get some kind of treatment, because at the very least none of them are perfectly corrosion resistant, and as you say, thread lubrication helps with tightening. What it really does is greatly reduce all the many factors that create friction in threads, usually into the negligible range, so that a given amount of torque applied to the fastener gives a more controlled amount of thread preload.

Most manufacturers say to install plastic bottom bracket cups dry.

Many have observed that over time, medium Loctite does a better job preventing loosening on M5 rack and fender bolts than grease.

Disc caliper and adapter mounting bolts are usually Loctited, or left with their pre-applied threadlocker. Probably the big reason is to ward off grease contamination.

Cantilever brake mounting bolts on brakes without an integral pivot are kind of an oddball, because tightening them in the 8-10 Nm or thereabouts range that applies to most other M6 bolts can result in the tip of the boss getting deformed. They should have medium threadlocker applied to the internal thread and then be very lightly torqued, around 3Nm. Because of the low torque, there's little thread preload and grease may make it loosen. But only plain pivot types - brakes with integral pivots, where the bolt shoulder or washer is contacting the brake and not the post, need a more normal amount of torque.

It's good to use anti seize instead of grease on all titanium threads, to prevent thread galling and seizing. I also use it on track cogs and singlespeed freewheels, because it helps ensure they can come off easily again after a hard life of constant torque. You can use it in a pinch on any thread you want to lubricate, the downside being it's messy.

Bearing grease is the normal practice for all threads on a bike you want to lubricate, because it's cheap, does the job well, and you need it anyway.

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    Which colour loctite do you mean by "medium" ? I'm used to seeing blue threadlocker which is low strength on bike parts and can be undone with handtools.. Medium is red and needs a couple hundred degrees C to loosen These temps are never seen on a bike and are overkill. High is car-brake level and needs about 500-600 degrees C to loosen. – Criggie Aug 5 '17 at 21:31
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    @Criggie By medium I just mean ones that are described as such on the bottle. Unfortunately there are enough variations, at least across brands, that the color by itself doesn't mean anything. Usually though, among the Loctite brand, blue is medium, and some typical ones would be 242 and 243. But on the other hand at work I often use a bottle of I think one of ND Industries Vibra-tite line that's a wicking medium-strength, and it's green. – Nathan Knutson Aug 6 '17 at 3:29
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I think Nathan Knutson covered the topic quite well, but I would like to round it out with one exception: the disc rotor bolts need blue Loctite threadlocker, because those usually thread into an aluminium hub, and yet they should stay immobile for the lifetime of the rotor. And they should stay fixed in place without relying on high torque, unlike most other fasteners on a bike. To compensate for this relatively low torque, you need a threadlocker.

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