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Servicing the Headset

The headset is the guts that attach your stem and handlebar to the front fork -- it's what lets you turn the handlebars to steer. You may need to service the headset to clean or replace the bearings, to tighten things up as the bike ages, or just to raise the handlebars.

If you notice a "cog-wheeling" sensation as you turn the handlebars, you probably have damaged bearings in the headset. You'll need a new set. Or, (much much worse) you've got damage in the steering tube's bearing races.

Headsets come in two varieties: (1) threaded, where the stem rises from the inside of the headset, and (2) unthreaded, where the stem clamps to the outside of a tube coming up out of the steering tube. If you have an unthreaded headset, go to the threadless headset page.

Threaded Headset Overhaul:

Begin by loosening the locknut slightly. (The locknut is the first thing below the stem that you can fit a wrench on.) On some bikes, the top lockring has a compression fitting

You may need to restrain the bearing cup (the other twistable object just below the locknut) as you loosen the locknut. Thin headset wrenches work best, but you can probably find something in the garage that works -- such as a channel lock plier on the bearing cup and a crescent wrench on the locknut.

If your only objective is to tighten a rattling headset, this is as far as you go in taking things apart. Tighten down the bearing cup until the headset has no "play" (see below) then hold the bearing cup still while you tighten the locknut down on top of it.

Now loosen the stem. (Some stems are held in place by a compression fitting of the locknut -- they'll already be loose at this point.) If there's a dust cap on top of the stem, pop it off. Insert a hex wrench into the bolt at the bop of the stem and turn until the handlebars move independently of the wheel.
Slide the stem out of the steering tube. Carefully place the handlebars in a position where you won't kink the cables! For example, you might use a wood clamp to attach the stem to the side of the steering tube. 

There will be a notched washer between the locknut and the bearing cup. Take it off.

Now loosen the bearing cup with your headset wrench (or whatever). I usually tilt the bike so the fork will stay in place. Put a big pan or cloth underneath, to catch any loose bearings.

Slide the front fork away from the steering tube. If the bottom bearings don't come out with the headset tube, reach inside the bottom of the steering tube and fish them out.

If the bearings aren't held in a clip, put them in a bowl and count them (top and bottom separately), so you get them back correctly.

Remove the bearings from the top of the steering tube.

Clean the inside of the steering tube. Check for dents in the bearing race (the curved area where the bearings roll).

Lube the bearing races with heavy grease.

Clean the bearings with degreasing solution. UtahMountainBiking sells degreaser solution, and all types of lubes and greases, at our on-line store.

If the bearings aren't perfectly round, they're worn. Replace them with new bearings.

Apply bearing grease to the bearings, working it into the spaces in the bearing clip.

Now put the bearings back where you found them.

Reinsert the headset tube into the steering tube.

Tighten the bearing cup until there's no "up and down play" of the headset in the steering tube. Some mechanics tighten until there's a bit of resistance to turning, then back off until the fork "floats" freely.
Put the notched washer back on top of the bearing cup.

Put the stem back into the headset tube. Set it to the desired height and snug down the locknut.

Put the front wheel back on (if you took it off). Look down to match the direction of the stem to the direction of the front tire. Tighten the stem into the headset with the hex wrench.

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