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Older bikes and children’s bikes are equipped with threaded headsets. This type of headset is designed to make it easy to raise and lower the stem whenever you want to change the height of the handlebar and adjust your riding position.
The headset’s top cup and the locknut that holds it in place are both screwed onto the steerer. The stem is equipped with a shaft, or quill, that fits inside the steerer. For safety reasons, you should never raise a stem above the limit marked on its quill.
On some even older headsets, the top cup screws down. Its serrated top edge is held in place by a clamp bolt on a similarly serrated lockring assembly. When the clamp bolt is loosened, the top cup screws off.
Remember to disconnect the brakes before you start working on the headset and make sure that you reconnect them when you are finished. Before the stem is replaced into the steerer of the headset, coat the quill with grease.
Right: Components of a threaded headset.
Step-by-step guide to Disassembling, adjusting and maintaining a threaded headset
1. Undo the Allen bolt in the stem center and knock it downward with a plastic mallet to free the steerer. The stem is secured into the steerer by an expander bolt, which, as it is tightened, draws a wedge up inside the quill.
2. Unscrew the locknut while holding the top cup still with a headset wrench.
3. Lower the fork to reveal the bearings in the bottom cup. Screwing the top cup upward allows this to happen. Although most headsets have ball bearings held in cages, watch out for loose bearings that may drop out of the bottom cup. Some headsets have roller bearings -- treat these as ball bearings in the following steps.
4. Degrease all the bearing surfaces of the top and bottom cups and of the races. You can access the top bearings by pushing the fork up the head tube and holding it there.
5. Grease both the top and bottom bearings or set loose bearings in grease inside each cup.
6. Screw the top cup down onto the top bearings. Replace the spacers and locknut.
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