Always amazes me how many right ways there are to a job on an internet forum
Aye well, or it's amazing how complicated the simplest of tasks can become.
Lest deal with three things,
1. The Dealer
2. The fastener and loctite
3. Why you should use copper ease.
Oh yes Lew maybe
4 - torque wrenches.
Oh god!
1. The DealerWhich kinda partly covers two. If the screw is tightened to the correct torque in this application then it will not come loose. An annual service should include a brake inspection and clean. The dealer will tell you to leave the servicing to them, that covers the brakes. The dealer either did not torque the mounting screws or did not apply enough torque (see 4). If you had your car serviced you might be a bit peeved if the brake callipers fell off - it's no different for a bike. Lew should complain to his dealer and his dealer should, if they accept his complaint, make him happy (I mean really make him happy - they focced up big style). Loose calliper mounts are unacceptable.
2. The fastener and loctite The primary purpose of the excercise is ensuring that it does not loosen unintentionally.
That is achieved by applying the correct torque to the mounting screw. Perhaps if somebody has the official Yamaha they can tell us if Loctite (or similar) is recommended. There is no mention of it in my clymer manual. Logically I don't think it would be.
When you use clean, grease free bolts in clean, grease free mountings with a decent dab of loctite and tighten to the correct torque, then the loctite will do its job and prevent vibration and heat cycles from lossening the bolt, while also provideing an anerobic seal which prevents the ingress of air, water, salt and other oxidisers, so reduceing corrosion. And the fact that you have used the correct torque means the bolt will not be stretched or damaged which in turn means it will come lose when the appropriate lossening torque is applied.
Indeed you need to prevent the ingress of water (we'll come to the reason for that in a moment) but to do so you need to cover the whole thread in loctite. Now we have a screw that goes into a soft aluminium thread and a darn good bond along it's entire length. There is now a danger (I think) that the loosening torque will considerably exceed the tightening torque and result in possible damage to the thread. Not a problem with a nut and bolt arrangement, if they seize for whatever reason get em off and throw away. Damage the thread on your calliper mount and you might want to cry. Do correct me if I am wrong, perhaps with your source, but I don't think is best practise.
3. Why you should use Copper Ease
Done your way, you increase the risks of seizing by encouraging corrosion by introducing copper, and you increase the risks of unintended loosening by introducing grease, so failing both objectives.
Cheeky foccer
What I have done is introduced an anti-seize compound to protect the soft aluminium threads. You are correct that the reason we have an issue here is due to two dissimilar metals. You may well find that many maintenance manuals do not mention the use of an anti-seize compound. The reason for this is, I suspect (and I'm taking a guess here), is that they are written in dry climates.
For the metals to react we need to introduce water to start the electrochemical process. You then get erosion of the most chemically active metal, in our case it will be the aluminium, plus you begin to form a bond. We need to protect that precious aluminium at all costs, we can't just throw it away like we could, if we wanted to, the screw.
So as we live in a wet climate (certainly I do in Ayrshire, umm though right now I think I'm stuck in the Bahamas!) we need a solution.
So we introduce our magical anti-seize compound. It's copper carried in a grease. The grease will exclude the water so hopefully we won't get any electrochemical reaction. But just in case, and with all that heat and yup water, our grease will very probably get burnt off or washed away, so we have the copper. The copper is nice and soft so we'll be able to get the screw back out but also it's gonna act as a sacrificial metal.
When the water gets in, as the copper is now the most active metal in our mix, it's the copper that will be eroded and in doing so protects our soft aluminium thread. Copper ease is perfect and recommended in our climate for use on brake calliper mounting screws.
4. Torque wrenches and settings. If you are worried about the torque setting when using copper ease, with a bit of googling you should be able to find correction tables for various anti-seize compounds. You need to also check the manufactures figure to make sure grease or anti-seize compound has not already been recommended and already factored in.
In my personal opinion, if you are going to use torque wrenches (not everybody will agree with this) then get good uns. I like Britool, but Norbar, Facom, Bacho and the like are all good.
If you really wanna get it spot on buy a quality torque wrench analyser and get it calibrated every other year (needs to be mounted on a solid bench by the way). Most of the torque wrenches we have at work have ranges marked on them but no scale. They are set up, checked for repeatability, locked and a certificate issued. They are then used and rechecked and part two of the certificate completed.
Me? I've been copper easing they brake mounting screws and nipping em up by hand (more accurate than a cheap torque wrench?) for over 20 years and I've never ever had one come loose and nor have I ever had a problem getting em back off.
So I suggest Paul that you pop your callipers off, clean all the loctite off the mounting screws and apply a thin smear of copper ease on the threads and reassemble.
Phew.