Now as it happens I recently got to know a nice chap Tom who is a professional motorbike mechanic, and he’d invited me over to his garage yesterday to see if he just happened to have a spare bolt that would fit to replace the missing one. Alas, no joy on the bolt, but it did give me opportunity to pick his brains about two things – threadlock and torque settings.
Firstly, threadlock – when a bike comes out fresh from the factory, most bolts are threadlocked (I imagine you’ve heard of this, but if not it’s a glue applied to the threads that sets hard once the bolt is in place), but from a motorbike mechanic’s point of view, if a bolt has to come out once, chances are it’ll probably have to come out again at some point in time. So he uses copper grease on the screw threads to ensure that the bolt won’t seize in place. Another issue that he has to consider is the bolt size – if it’s M12 or above with a prober hexagon head, chances are the force required to undo a threadlocked bolt won’t damage the head, but the caliper mounting bolts take a small (6 or 7 mm) allen key, so if too much force is used there’s a risk of rounding the head – not good!!
So the conclusion was to use copper grease, not threadlock, and be sure to tighten the bolt up correctly..
And that leads me onto the next topic – torque settings – you see although I have a Haynes manual for the bike, the brakes are non-standard – they are off a GSXR750, and they don’t use either the bolts from the GSXR750, or for the ZZR1100 – they are special shouldered bolts – so there is no specified torque setting that should be used…
So what to do – well as Tom pointed out, with life and use, bolts can stretch, and original torque settings cannot always be relied on. Instead, he relies on his experience to know by feel what the right pressure is. Now that may not be so helpful for the amateur mechanic, but it does make common sense – most guys who’ve done a bit of spannering pretty much know by feel how tight to go.
My thoughts therefore run along the lines of – copper grease, tighten up good and tight, but don’t overtighten, and last, but perhaps most important, come back after the first ride or two, and CHECK and RE-TIGHTEN if need be!!!