Headset Replacement or Overhaul
Headset replacement requires expensive special tools, so unless you're really into bike mechanics it's probably best to take it to a shop.
It's questionable whether it's a good idea to spend tons of money on a new headset. Some extremely expensive headsets don't do any better job than modestly priced ones, and they require a headset press unique to them. For example, if you throw your wad at a Chris King headset, make sure your pals notice it--the only thing they are superior for is posing.
Headsets and forks come in sizes (diameters), usually 1", 1 1/8" or 1 1/4". Be sure to buy the right size.
See the Fork article for the procedure to cut a new fork steering tube. Link here for photos of headset parts.
Threadless Headsets
Tools needed to replace a threadless headset:
work stand
hex wrenches, usually 5 mm and 6 mm
fork crown race remover--either a special tool or (what I use) a hammer and flathead screwdriver
head tube bearing cup remover--aka cup remover
headset press
fork crown race setter
Tools-Top to Bottom-Crown Race Setter, Headset Press, Bearing Cup Remover
A headset press is very expensive. To make a press on the cheap, see the fredset article.
The procedure to replace a threadless headset is:
1. Put the bike in a secure work stand.
2. Disconnect the brake cable and remove the front wheel, so you can remove the fork.
3. Remove the stem and then the fork.
4. Remove all the loose headset pieces, and keep them in the right order and orientation in case you need to reuse them. Don't forget which way the ball bearing retainers face.
5. Clean everything you can reach.
6. If you are overhauling the headset instead of replacing it, make sure all the parts are in good shape, repack the headset races with bike-specific grease and put it all back together.
7. Knock the fork crown race off the fork. There are several ways to do this. I prop the fork upside down with the steering tube on a work bench or the floor, then tap the crown race off with a flathead screwdriver and hammer. Tap it off carefully, a little bit at each place. You don't want to bend anything.
8. With the cup remover, knock the top and bottom head tube bearing cups out of the bike's head tube.
9. Take the new headset out of the box, and keep it all in the right order.
10. Install the new crown race. Slip it on the fork concave side up until it stops at the little bench at the bottom of the steering tube. Slam it on with the fork crown race setter. Really wang it--it has to be all the way on and flush. If the crown race is a little too tight, you can file the little bench down some.
11. Press the head tube bearing cups into the bike's head tube, using a headset press. In the third world, folks knock them in with a 2 x 4 and hammer, but good results are not guaranteed.
12. Put the bottom ball bearing retainer on the fork crown race and insert the fork in the bike's head tube, applying bike-specific grease between the races. Hold the fork on the bike.
13. Drop the top ball bearing retainer over the fork steering tube and onto the upper tube bearing cup, applying grease to the retainer.
14. Place the top bearing cone over the fork steering tube and on the top of the ball bearing retainer.
15. Wedge the plastic compression ring between the fork and the inside of the top bearing cone.
16. Drop spacers over the fork steering tube, and then install the stem, so the lip of the top of the stem is higher than the lip of the fork.
17. Put the top cap on over the stem, making sure the top cap is sitting on the stem--not on the fork.
18. Thread in the compression bolt and adjust the pressure on the ball bearing sets. You should be able to rotate the fork freely without resistance or catching, and there must be absolutely no lateral play in the system.
19. Tighten the bolts on the stem. Do not over-tighten--they strip easily.
20. Test the headset. Adjust the headset if necessary.
21. Reattach and adjust the brakes.
Threaded Headsets
The tools and procedures for replacing a threaded headset are the same as for threadless systems, except:
Headset wrenches are needed.
An adjustable cup/top bearing cone is threaded onto the fork steering tube, followed by a lock washer and locknut, and then a quill stem is inserted into the fork steering tube.
The adjustment procedure is slightly different.
