Front wheel installation, although simple, is a little more involved than just slapping the parts together and tightening the bolts. If you don't pay attention to how you do it, the fitment will not be right. This means the clamps may not hold the axle correctly or the forks may be misaligned. Fork misaligment will result in oil leaking and in extreme cases, accelerated slider bushing wear. Not all front wheels are mounted as in this example, but most modern motocross bikes are like this and many other bikes are at least similar.
1 Take a good look at the axle here. The end opposite of the threads has a larger diameter than the rest of the axle. When the axle is in place and tightened with the axle nut only, this shoulder pulls the wheel hub tight against the the fork on the nut side.
2 A complete assembly gives more perspective. On the shoulder side of the axle, the fork leg has nothing to do with securing the wheel hub itself. On this side there will typically be a gap between the fork leg and the wheel spacer.
3 View of wheel with a spacer removed. The spacers serve two functions here: 1) Extension of the inner bearing races for fit between the forks and 2) dust shields. It is good practice to clean here.
4 On the nut end of the axle, the wheel spacer will be tight against the fork leg. Thus, all bearing preload is accomplished via the fork leg on the nut side.
5 After the axle is inserted throught the forks and wheel, tighten the axle nut against the fork lightly. Do not torque the nut yet, but make sure it is fully threaded and tightened enough that the axle is pulled through all the way. The shoulder of the axle should be holding the wheel assembly snug against the fork leg on the nut end. The axle will be floating in the fork on the throttle side (axle shoulder end).
7 The problem now is how to clamp the floating side of the axle while also achieving proper fork alignment. Because of normal internal clearances, it can be difficult to get acceptable alignment. Putting a side load on a fork leg while tightening the pinch bolts will also cause misalignment.
8 There are a few ways you can align the forks. A widely accepted method is to compress and release the forks several inches a few times. The idea is the floating fork tube will align with the natural fork mounting, resulting in aligned forks. While this method is an option, it does have some short comings.
9 Another method, far superior to compressing the forks (not to mention easier) is to use a fork alignment tool. The tool is set to the span of the forks at the mounts where they are rigid. The preset tool can then be used to maintain proper fork spacing while the axle is clamped in place. This method assures true parallelism. The negative aspects of this are:
10 Another option is to tap on the floating fork leg. This must be done with the bike on a stand and the wheel not contacting the ground. The idea is this: Fork alignment is already dictated by the triple clamps. Firmly tapping on the floating fork leg causes vibration at the axle mount. While tapping, the fork tends to float on the axle to its aligned position. Keep tapping until the axle settles in to a position. I use this method all of the time with good results, but it also has some disadvantges.
Additionally, you must use discretion with what you tap with. A steel or brass hammer is ok so long as you use a piece of wood as a striking surface. The best option is a weighted plastic hammer as you see here.
11 Finally, when alignment is assumed to be correct, apply blue Loctite to the ends of the bolts and tighten them (evenly, in increments) to the specified torque.
To really be serious about nailing your fork alignment, an alignment tool is the best choice. None of the methods described here, however, can compensate for forks poorly mounted in the triple clamps nor for bent fork tubes.
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