Wednesday, September 16, 2009

Fitting Disc Brake Rotor Bolts

Tips for Fitting Disc Brake Rotors to Mountain Bikes (6 Bolt Fittings)The international standard uses six bolts to attach the rotor to the hub. The picture below (left) shows a Shimano XT hub with the rotor removed so you can see where the six bolts would fit.BoltsMaterials / Quality: Disc brake systems generate a lot of force and so you should always use good quality high tensile bolts. If you want to save weight titanium is one (expensive) option but I would never recommend using aluminium alloy bolts. Stainless steel are attractive because they stay shiny, but I use high tensile steel bolts which are stronger. These are coloured black so they look good on any bike.Bolt heads: Some bolts come with a Torx head (roughly star shaped) and others with a standard hex/allen socket head. The latter tends to be easier because most people have allen keys whereas torx are a bit more obscure. Also most bike multitools have a range of allen keys but seldom a torx key (which is a real pain if you are far from home).FittingThread Preparation: Use a non-permanent thread locking compound (e.g. Loctite 243 Lock 'n Seal - try Halfords, Robert Dyas or search for 243 / threadlock on ebay) on your bolts. Firstly this will seal the thread against water and so the bolt won't seize in the hub. Secondly threadlocks, as their name suggests, keep bolts in place. Mountain bikes are subjected to lots of vibration which can cause bolts to come loose, especially where they weren't adequately torqued initially. I can tell you from personal experience that rotor bolts coming undone is a BAD thing. Please don't skip this step - in my opinion it is an essential safety precaution.Installing the Rotor: Most rotors are intended to function in a particular direction so check the manufacturer's instructions and/or look for markings on the rotor itself (e.g. Hayes use an arrow to show the direction of rotation).Torquing the Bolts: Bolts should be installed in a 1, 3, 5, 2, 4, 6 pattern.This reduces the chances that you will distort the rotor. Bolts should be fitted using good quality tools. Avoid using ball-ended allen keys (below, left) which can start to round off the bolt heads. Allen keys with a 90 degree end (below, right) are a better choice.Once fitted, give the threadlock a few hours to cure before riding the bike. After your first ride, and as part of your regular maintenance, check that your rotors are securely fitted and all the bolts are still tight.Removal: Threadlock normally comes undone with the use of hand tools. When refitting you should reapply some fresh threadlock. Bolts can be reused many times, but if you think they are damaged or you have started to round off the heads then buying fresh ones is a good plan.Happy riding!

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