Okay so forgot all my knowledge (very little) from the past and have used finish line teflon grease on my stem bolts.
This stuff - http://www.wiggle.co.uk/finish-line-teflon-grease-455g-tub/
Now if I look up on google there's pictures of bolts breaking easier if you use a load of teflon grease in high stressed areas admittedly for a bike sure the loads are fine. Anyway, shall I get the degreaser out and get rid of the grease and use some copper grease and just start again.
Sorry very interesting morning topic but whatever any help much appreciated and if anyone has done the same please chip in so I don't feel like an newbie putting bearing grease on bolts plus a confirmation it's not as bad as these internet tests make out surely grease is grease
Wipe it off, you'll be fine, I never grease stem bolts anyway.
I used car wheel bearing grease on everything for years. I'm sure you'll be fine. Copper grease on none moving parts is the way forward though.
It's fine, I use whatever's closest for non-moving parts (copper slip or Silkolene Pro RG2) and I've never sheared anything.
And unlike IHN I always grease stem bolts.
I've never heard of such a thing.
What's the causal mechanism? Over torquing because the threads are lubricated?
I always grease all bolts. Except rotor bolts, which get threadlock, but if I'm brutally honest that's largely because they come with threadlock already on them. No problems yet in 30 years of bicycle maintenance. Your awesomeness may vary. 😉
Why does teflon grease result in broken bolts? Over tightening due to low friction?
What’s the causal mechanism?
Exactly.
Sounds nonsense, grease away.
Yes - why should they fail?
Too little friction with teflon? Means torque will stretch the bolts too much? Mmmhh
Use lower torque then?
No idea.
I've seen plenty of parts manufacturers recommend torque settings, some specify grease, and some don't.
And unlike IHN I always grease stem bolts.
And neither of us are dead, so it clearly doesn't matter one way or the other 🙂
Means torque will stretch the bolts too much
Only if you over torque. I have no idea of any torque standards in the bike industry, ie if there is even a standard, but at work all our torque figures are quoted under the assumption that threads have been lubricated, be it with grease or threadlock. If you over torque, you are taking the bolt beyond it's elastic limit, and you don't want to do that.
Other industries may differ.
As nobeer' said, some torques are given with lubrication applied, some are dry.
Typical examples, the bolts holding your towbar on should be dry because they're on for life, oil filters are obviously wet.
Lubrication adds about 70-100% more tension on the bolt, which when most are specified to be as tight as possible without causing damage (crushing components, stripping threads) mean you'll be massively overdoing it.
I always assume all bike torques are with threadlock applied because that's how they come from the factory.
Standards, in the bike industry.....
Critical applications normally spec the lube, eg ARP studs come with ARP lube which will give a relatively reliable clamping force when torqued if unable to measure stretch. Using the same applied force can result in a different clamping force as components burnish when repeated.
I always assume all bike torques are with threadlock applied because that’s how they come from the factory.
Depends on the manufacturer, some stem bolts come with blue loctite, some come greased.
I don't think that stem bolts are designed to be that tight on tolerance to potential failing. They aren't a particularly high tech or compromised solution, they're just external bolts. Ergo, give em a wipe and don't worry about it!
I don’t think that stem bolts are designed to be that tight on tolerance to potential failing. They aren’t a particularly high tech or compromised solution, they’re just external bolts. Ergo, give em a wipe and don’t worry about it!
I doubt 5Nm is anywhere near the limit for the alloy threads, but I'd be worried about getting it wrong for the sake of the bar!
You are probably more likely to round the head than you are to take the bolt past its elastic limit.
but I’d be worried about getting it wrong for the sake of the bar!
Very sensible point. Not worrying about it means just don't do anything weirdly out of the range of normal and don't sweat it! Nip them up, but don't do so excessively just because a bit of grease has got on there!
All the instructions I've read specify greasing the threads.
You may get some variation, but unless they specify a specific grease, the specified torque value shouldn't over-stress the bolt.
If you want a specific load you're much better specifying a low torque and then an angle, but that could get silly with stems (and there are then additional variables in the system like the stiffness of the section of bar/stem etc - it's quite a complicated joint as far as these things go - this unfortunately also means that bolts are subject to fatigue so the normal rule of if the bolt's yielded a bit it doesn't really matter as it's basically a static force once clamped up doesn't apply - if it's yielding locally the fatigue life will be much lower).
There are means of getting an accurate preload, but they're overkill for stems. If that ARP graph is correct (and it may well be) it's for an unusually heavily loaded bolt - which isn't unusual for a cylinder head etc. where the assembly and relative stiffness of the bolt and cylinder head/block assembly mean you don't have fatigue problems in the bolt and any low preload will have head gasket failure consequences. Often new bolts are recommended, or stretch limits specified, for this kind of application.
You are probably more likely to round the head than you are to take the bolt past its elastic limit
If you have shit tools, and don't use a torque wrench.
