Headsets are remarkably simple to service, needing no special tools at all, just one (or two) Allen keys, degreaser or other cleaning agent and good-quality grease.
Headsets, like bottom brackets, are frequently ignored, gradually deteriorating without you noticing. Regular servicing will help keep them turning smoothly and will make your bike feel more responsive. Cleaning the dirt out and replacing the grease with fresh stuff will help make the bearing surfaces last as long as possible. With the ball type, it’s worth replacing the bearings at every service – new ones only cost a couple of pounds. Cartridge bearings are more expensive and can usually be resuscitated for help servicing them. If they need replacing, always take the old cartridge bearings along to your bike shop to match up new ones. The size and shape are crucial.
Check carefully for pitting on bearing races once you’ve cleaned out the headset. Even very tiny pits are a sign that your headset needs replacing. The surface that suffers most is the crown race, the ring at the very bottom of the headset that’s attached to your forks. Your bearings will quickly wear a groove in this, showing you where they run. The crown race should be completely smooth. You should be able to run a fingernail around the groove without it catching in any blemishes on the surface.
Headset replacement is a job for your bike shop. The new headset needs to be pressed into your frame, with the top and bottom surfaces exactly parallel; otherwise the headset will wear very quickly and bind at some handlebar angles. The cups are a tight fit and so must be pressed in carefully to avoid damaging the shape of the head tube. Ignore anybody who tells you that it’s fine to fit new headset cups by bashing them into the head tube with a block of wood.
Before you start, remove the front wheel altogether. It’s easiest to do this job if you disconnect either the front brake lever from the front brake or the front brake lever from the handlebars. This way you won’t damage the cable or hose when you remove the forks.
With cable brakes, disconnect the noodle from the brake (don’t undo the fixing bolt, just quick-release it), line up the slots on the barrel-adjuster with the slot on the lever, pull the cable gently out and wiggle the nipple free from its nest inside the brake lever.
With disc brakes, have a look at the lever. If it’s fixed on with two bolts on either side of the handlebar, simply remove them both, untangle the hose from the other cables and tape the lever to the forks to stop the hose getting snagged on anything. Otherwise, remove the handlebar grip on the front brake side, loosen the brake-fixing bolt, and slide the brake lever off the end of the bars.
Untangle the hose from any of the other controls and tape or tie to the fork leg.
Step 1: Undo the Allen key on the very top of the stem, the top cap bolt. Remove the top cap completely, revealing the star-fanged nut inside the steerer tube. Undo the bolts that secure the stem while holding onto the forks, and the stem should pull off easily.
Step 2: Tape or tie the stem to the top tube out of the way (protect the frame paint with a cloth).Pull off any washers and set them aside. Pull the forks gently and slowly down out of the frame.
Step 3: The fork may not want to come out. Lots of headsets have a plastic wedge that sits above the top bearing race and that sometimes gets very firmly wedged in place. Release it by sliding a small screwdriver into the gap in the plastic wedge, and twist slightly to release the wedge. You could also try tapping the top of the fork with a plastic or rubber mallet. Don’t hit it with a hammer – that’s not the same thing at all.
Step 4: Catch all pieces as they come off and note the orientation and order of bearing races and seals.
Step 5: Once you’ve got the fork out, lay out all the bearing races and cups in order. Check the bearing cup at the bottom of the head tube for any bearings or seals left in there. Clean all the races carefully: the ones attached to the frame top and bottom, the loose one off the top chunk of bearings when the fork came out and the crown race still attached to the fork. If you have cartridge bearings, see the section on servicing the cartridges.
Step 6: Look carefully at the clean races and check for pits or rough patches. Pitted bearing races mean a new headset. This needs special tools and so is a job for your bike shop. Otherwise, clean all the bearings and seals carefully. If you used degreaser, rinse it off and dry everything. Grease the cups in the frame enough that the bearings sit in grease up to their middles. Cartridge bearings just need a thin smear to keep the weather out.
Step 7: Don’t grease the crown race on the fork or the loose top head race. Fit a bearing ring into the cups at either end of the head tube and replace the seals. The direction the races face is crucial, so replace them facing the same direction they were. Slide the fork back through the frame and slide the loose top race back down over the steerer tube. If it had a plastic wedge, put it on next, followed by any washers or covers in the order they came off.
Step 8: Refit the stem and any washers from above the stem. Push the stem firmly down the steerer tube.
Step 9: Make sure there’s a gap of 2–3mm (around 1⁄8 inch) between the top of the steerer tube and the top of the stem, adding or removing washers if necessary. Refit the top cap, then adjust bearings. Tighten the stem bolts securely, then refit your brake lever or cable and your front wheel. Check your stem is tight and facing forward. Also check that your front brake is working properly.
Checking the condition of the steerer tube
While you’ve got the forks out, it’s worth checking the condition of the steerer tube. This will break if abused, so it is worth inspecting regularly. Adjustment of the bearings also depends on the stem being able to slide easily up and down the steerer tube when the top cap is tightened or loosened.
- Hold a ruler up to the steerer tube. The side of the ruler should lie flat against the length of the steerer. Any bends in the steerer will show up as gaps between it and the ruler. Gaps greater than 1mm (1⁄16 inch) mean that the steerer is bent and should be replaced
- Feel along the surface of the steerer with your fingers. There should be no bulges, dips or irregularities in the diameter of the steerer
- Check for cracks, especially down at the bottom of the steerer tube, near the crown race
- Check that the crown race is a tight fit on the forks – you should not be able to move it with your fingers
- Check the area that the stem bolts onto. It’s important that this is clean and smooth. Some stems will damage the steerer if overtightened – replace if it is distorted
- The top of the steerer must be smooth. If you’ve cut down the steerer, file the cut surface so that there are no overhanging snags of metal – these will get caught in the stem and prevent you from adjusting the bearings
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “Aheadsets: adjusting stem height”