Originally Posted by ParkTool

Headset Bearing Adjustment

Threaded headsets are adjusted using a top locknut and threaded adjusting race. The stem does not have to be removed to adjust the bearings. Generally, the best bearing adjustment is as loose as possible, but without bearing play or knocking. To achieve this, the following procedure will first create play in the adjustment, and then proceed to incrementally tighten the race until play is gone.

1. Use a headset wrench to hold lower race (adjustable race).
2. Using a large adjustable wrench or the Park Tool headset wrench HW-2, turn locknut counter-clockwise to loosen. Lower race is now free to turn.
3. By hand, turn lower race clockwise until it contacts ball bearings.
4. Turn race back counter-clockwise at least 1/4 turn from this setting. Hold adjustable race with headset wrench and tighten locknut. Tighten locknut fully, see Appendix B for torque. This early setting is intended to have play.
5. Check for play by pulling back and forth on fork. A knocking sensation indicates play. Turn the handlebars in different directions while checking for play. There should be play at this early setting. If headset feels tight, loosen adjustment further until play is found. Use care with suspension forks, because the legs may have play in sliders. Grab upper portion of fork.
6. If play is present, grab front wheel between knees and hold it in line with top tube. Lower adjustable race will need to be adjusted SLIGHTLY clockwise. Use a wrench to hold lower race and note orientation of wrench.
7. Loosen locknut and move wrench holding adjustable race clockwise 1/32nd of a turn. Front wheel must be straight to gauge adjustment.
8. Hold adjustable race from moving and tighten locknut fully. Check again for play, rotating fork and checking different positions.
9. If play is present, repeat steps "6" and "7" above until play disappears. Adjustment is finished when there is no play in any position as the fork rotates.

NOTE: Another test of play is to place the bike on the ground and grab the front brake tightly. Press downward on the handlebars and rock the bike forward and back. A knocking sensation may indicate a loose headset. In effect this does the same thing as grabbing and pulling on the fork. However, play in the brake caliper arms may also cause a knocking. Front suspension forks may also have play in the legs, which can cause a knocking. If the adjustment seems very tight after adjustment, there may be other problems in the headset. Bearing surfaces may be worn out, or the ball bearing retainers may be upside down, or a seal may be improperly aligned. If play always seems present no matter the adjustment, the threaded steering column may be too long for the locknut. Add headset washers under the locknut in this case. If this is not the problem, cups may be loose in their press fit in the frame.

Bearing Adjustment and "Feel"

Bearing surfaces are made from hardened steel. The surfaces are cut typically by grinding. Round ball bearings roll on the curved surface of the cup and cone. Even the highest quality bearing surfaces will have slight grinding marks. In the left image below is a high quality cone magnifed two hundred times. Notice the parallel marks from the grinding stone. Also note a slight pit from wear. The right hand image is a bearing magnified the same amount. It does show some surface marking, but is generally smoother than the cone or cup. Bearing surface smoothness will vary between manufacturers and between models. Some bearing system will simply "feel" smoother because they are smoother. This is why it is difficult to adjust by using a subjective feeling of smoothness. Generally, adjust bearings for the loosest setting that has no knocking or play, regardless of this relative smoothness.

Originally Posted by askrom

I see! In short, adjust the threaded race just enough so there is no play, then lock the locknut tightly against the threaded race so it won't move. For this, I'll absolutely need to use two wrenches, not my wacky one-wrench method.

Thanks!