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Headset Adjustments (continued)

Threadless headsets make good engineering sense. As compared to their threaded counterparts they are stronger and lighter, not to mention easier to manufacture. A threadless system allows the steerer tube to pass completely through the stem and eliminates the locknut, as the stem clamp is what ultimately holds the system together. Threaded headsets adjust independently of the stem via the threaded adjustable race and locknut and require a quill stem that inserts into the steerer, expanding to hold in place. The one advantage of a threaded system is the ease of handlebar height adjustment, which doesn’t require any swapping of spacers or readjusting the headset as in a threadless system. In most cases the upper and lower head races are press fit into the frame using tools made for just that purpose, but in recent years certain threadless systems have come about with the races integrated into the headtube.

Diagnosis and Adjustments
Headsets are either too loose, too tight or just right with little room for error in between. Too tight is easy to diagnose–any resistance to turning is too much, it should be silky smooth side to side. Loose headsets are just as easy to diagnose either through knocking while riding or this simple test–grab the lower head race with one hand and the stem with the other and rock the bike fore and aft. Any movement is evident of a loose headset.

In a threaded system, rotate the adjustable cup up and down a quarter turn at a time to adjust the bearing load and keep it in place by tightening the lock nut against it once in adjustment. A threadless system requires you to loosen the stem clamp and adjust the bolt directly on top of the steerer tube which controls the bearing load before tightening the stem clamp once again to lock it in place.
Is the headset loose in some places and tight in others? This could mean one of a few possibilities. The steerer tube may be slightly bent from a front end impact, the frame headtube is warped or the races are installed incorrectly. In the event of the races being the culprit, it may be that they have been pressed into the frame unevenly and/or that the headtube needs faced to ensure the upper and lower surfaces of the headtube are free from paint and absolutely parallel to each other. Each of these possibilities likely requires a trip to the local bike shop for absolute diagnosis and the appropriate medicine to fix the problem.

In headsets with loose balls it is fairly common for a neglected headset to feel indexed as each ball lines up with an indentation formed in the lower head race from lubricant breakdown. While this is usually the beginning of the end of a headset, one can sometimes stretch the service life simply by knocking the lower head race from the frame, rotating it 90° and pressing it back into the frame. This effectively moves the indexed part of the steering to 90° from center, a place that one never encounters while riding, leaving you with a new-ish feeling headset for a while at least.

Preventative Maintenance
The best preventative maintenance for a headset is to keep it in adjustment and well greased. Riding around with a loose headset for any period of time is just asking to replace it as few things other than a crash can wreck the bearing surfaces sooner. Keeping it lubricated is easier said than done as the front wheel tends to spray a perfect storm of water and grit directly into the lower bearing. Using a high quality, marine grade grease is your best bet to keep water at bay. Clean and replace the grease as necessary depending on your riding climate–more often in wet climates than dry.

There is much more to be said about the finer points of headsets than covered here. This primer is meant as just that, enough information to be dangerous but hardly a total guide to everything headset related. For futher resources see the extensive entries on the subject at the late Sheldon Brown’s website:

    Top left image, left to right: crown race, bearing, lower head race, upper head race, bearing, adjustable race.