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May 1, 2012 Mechanics No Comments

Now that it’s bike building season again, I’m going to try and run through the building of an entire bike from scratch. So to start with, here’s some tips for headset installation. The headset comprises a set of bearings and their containers which sit at each end of the head tube. You have the forks at one end and the handlebars and stem at the other, with the steering column running through the head tube. The bearings ensure a smooth rotation of the steering column. A worn out, damaged or incorrectly installed headset can lead to problems with the steering, from it being too slack, to too stiff.

Firstly you need to work out what kind of headset you are dealing with. It will likely be either threaded or threadless, both of which have a set of cups protruding from each end of the headtube. Threaded headsets are found on older bikes and retro builds and will likely be 1” diameter. Threadless, also known as an aheadset, is likely to be 1 ⅛”  and is pretty much found on any modern bike but you can also get them in 1” size as well. If your headset does not require cups, then it is an integrated or semi-integrated headset, which means the top of the head tube actually performs the job of the cups.

These diagrams break down the construction of both threaded and threadless headsets, with an integrated headset appearing much like a threadless one without the cup assemblies.

You might already have a set of cups installed on the frame. If you do, but don’t have the rest of the headset, then beware. While some headsets will mix and match no problem, many won’t. If you have a complete headset to install, it’s best to knock the cups out and use the whole thing. The main issue I’ve found is that headsets are designed to use many different types of bearings. From loose ball bearings, to caged bearings, to cartridge bearings. Now you can replace loose bearings and caged with one another, but cartridge bearings require a slightly different shape cup.

You can read an older article of mine on how to use a homemade headset press to get your new cups in here. Just be careful to get them in straight, otherwise you risk deforming the headtube.

Just installed the crown race. You can just see that this one is a 'split' race, making it easier to get on. And off!

Now working from the bottom up, you need to install the crown race on your fork’s steering tube. This rotates with the lowest set of bearings to make the fork turn smoothly. You might be lucky and find that your race slips all the way down without much trouble, but more likely it will need encouragement to get flush with the top of the fork. Your best option here is to use a length of plastic pipe that fits quite snug over the whole steering tube and tap the top of this with a mallet to seat the race. I’ve also had success with a long blade screwdriver and a rubber mallet, just tapping it gently all around. Careful you don’t pit the race though, as it needs to be smooth. I find an old inner tube is often useful to protect the steerer. What’s also good is to wrap an inner tube around the steerer and seat a large adjustable wrench over the race. Then tap the side of the wrench with your rubber mallet. Just be really, really careful doing any of this with a carbon steerer. Remember that a good scratch can destroy the integrity of carbon structures.

Now you drop a set of bearings ‘face down’ on top of the crown race. The bearings may already be mounted inside the cups and there may also be a rubber seal that sits in between the bearings and the race, depends on what your headset needs.

Stick the steering tube through the headtube, then set another set of bearings ‘face down’ inside the top cup. Again there may or may not be another rubber seal here. A threadless headset will have a compression ring, that sits on top of the bearings here – you can see this on my integrated headset in the photo. Next, you will add the top bearing cover. On a threadless and integrated headset, this just drops on, over the steering tube. On a threaded headset it screws on, so the fork is actually attached to the frame even without a handlebar stem attached.

You should still have a bit of steering tube protruding. For threadless headsets you will cover this excess with the required number of spacers and then mount the ahead stem. Or you may not need any spacers if you like a low setup.

On a threaded headset however, you need to install a washer and a locknut to keep the setup tight. Now it’s important to have measured your steering tube so that it will go through the headtube and the height of the headset stack, with just a little left over to screw the locknut onto. If you’ve got a bit too much space because you’ve got a headset with a low stack height or whatever, there are spacers available for this setup too. Screw the locknut down nice and tight. For the threaded headset, you’re done.

Here you can see the top of the cartridge bearing in blue, and the compression ring in red

For the threadless however, you’ve got to mount the ahead stem (handlebar stem) and clamp that down to keep the steering column and forks in place. To top it off, you need to install a star nut and top cap, which I explained how to do in this earlier post. Carbon warning: If you’re using a carbon steerer then don’t install a star nut, instead use a compression plug that can safely grip the side of the steerer. Then install the top cap, making sure you’ve got the whole setup on tightly, so there’s no ‘give’ if you lift the front end of the bike up. The forks should rotate freely, but not wobble around.

Here you can see the top of the steerer, ready to accept the ahead stem. Note the compression plug in the top of the steerer as this one is carbon. A couple of spacers to cover the excess steerer tube length and the Alpina top bearing cover.


Written by james

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