The bearings are adjusted for no play at all, while allowing the fork and bars to rotate smoothly in the frame without resistance. Use the steps to check the adjustment if they’re tight or if there is play. You wear your bearings really quickly if you ride them either tight or loose.
It’s vital to check that your stem bolts are tight after finishing this job – it’s easy to get carried away with doing the adjustment and forget to finish the job off. Some people will tell you to leave your stem bolt slightly loose, so that in the event of a crash your stem will twist on the steerer tube rather than bending your handlebars. You should not do this. The consequences of your stem accidentally twisting on your steerer tube as you ride are far too serious and dangerous. Always tighten your stem bolts firmly. It is fine to slacken the topcap bolt off though – it’s only needed for headset adjustment and can be a handy emergency bolt if something else snaps!
Step 1: Loosen the stem bolt(s) (A) so the stem can rotate easily on the steerer. Undoing the top cap (B) makes the headset turn more easily; tightening it eliminates play. Approach the correct adjustment gradually, testing for
rocking. It is easier to get the adjustment right by tightening a loose headset than by loosening a tight one. If the headset is too tight, back off the top cap a few turns, hold on the front brake and rock the bars gently back and forth.
Step 2: Slowly retighten the top cap, checking constantly, and stopping when you’ve eliminated all the play. Remember to check for play with the bars turned to one side, so that you can be sure that any knocking you feel is the headset, rather than the brake pivots or fork stanchions.
Step 3: Once you have the adjustment correct, align the stem with the front wheel and firmly tighten the stem bolts. Check the stem is secure by holding the front wheel between your knees and twisting the bars. If the stem shifts on the steerer, the stem bolts need to be tighter. Check the adjustment again and repeat if necessary – sometimes tightening the stem bolt shifts everything around.
- Allen key to fit stem bolts
- Allen key to fit top cap (Both of these are almost always a 5mm or 6mm Allen key, although you may occasionally come across a 4mm Allen key fitting)
Adjusting stem height
- The same Allen keys as above, to fit your stem bolts and top cap Servicing
- Allen keys as above
- Tools to disconnect your brake cable, lever or disc calliper – almost always the same Allen keys as above – 4mm, 5mm or 6mm Allen key
- Degreaser to clean bearing surfaces
- Good-quality grease – preferably a waterproof grease such as Phil Wood
- Fresh bearings: ball bearings for headsets are generally 4mm (5 ⁄ 32 inch), but take your old ones to your bike shop to match them up (Bearing races can be replaced by loose bearings, which are more fiddly to fit but roll more smoothly and last longer)
(Cartridge bearings should be taken to the shop to be matched up for fresh ones – there are a few different types in use, all of which look very similar)
(The most common type, for Shimano bearings, also fits in headsets made by other manufacturers)
Cutting down steerer tube
This is the most tool-intensive job you can do to your Aheadset!
- All the servicing tools above
- Vice to hold steerer tube while you cut it
- Soft jaws or an improvised tube clamp to protect steerer tube from vice
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “Headsets”