You're going to need: allen key (usually just a 5mm), grease and grease gun, container, clean rags, possibly a mallet or hammer and piece of wood, metal rod and assorted other non-tool workshop bits and pieces as described in the text for a threadless headset; all of the above and a headset spanner for a threaded quill headset. An old mountain bike inner tube, some zip ties and a sharp knife or scissors.
There are three basic types of headset and they're very easy to tell apart simply by looking at the stem...
Disassembling the headset is a concept that scares some people, mostly because the headset is all sealed away inside the frame where you can't see it and so they imagine it contains all sorts of complicated, fiddly bits that are going to leap out and vanish forever under immovably heavy bits of furniture the moment they even go near it with an allen key.
The good news is that headsets are extremely simple. The bad news is that if you have one with free - as opposed to caged or cartridge - bearings, they will be looking for opportunity to escape. The other good news is that it's easy to foil their plans.
Disassembling a Threadless Headset
(image credit: keithonearth
CC BY-SA 3.0)
Next, remove the top cap. Most examples are unfastened with a 5mm allen key, but there are a few that use other sizes. It's a conventional thread and unscrews anti-clockwise - the first turn might be stiff, but it'll soon free up (if you're restoring a bike and it won't come undone, spray a bit of penetrating oil around the bolt head and give it a few minutes to soak through). In most cases, the bolt is short and screws into a star nut located within the steerer tube - however, star nuts are notoriously difficult to insert and as a result are often replaced with either an expansion device that expands as the bolt is tightened, locking it into the steerer or with a much longer bolt that passes right through the steerer to a bottom cap. Expansion devices will usually remain within the steerer and can be pushed out the other end with a piece of dowel or with a broom handle. The bottom cap - unless it's rusted in place - will fall into the container. With the bolt removed, the cap should lift off.
Note here that, in addition to the four diameters, there are also three types - conventional, integrated and internal. In the case of a conventional model, the head tube races press-fit into the head tube of the frame; in an integrated model the races are actually machined into the head tube (with the various drawbacks that entails) and in an internal model the races fit inside the head tube and are completely contained within it when the headset is assembled. All three are dismantled and reinstalled in the same manner.
|Star nut, top cap and tensioning bolt
If the pinch bolts have seized
Sometimes, if a bike hasn't been correctly maintained, the pinch bolts will seize in the stem. Usually, penetrating oil will free them but in extreme cases it may become necessary to use drastic measures: whether you wish to carry this out yourself or pay the bike shop to do it depends on your skill and bravery. Using a pair of Vernier calipers, measure the diameter of the bolt heads. Then, using a metalwork drill of equal diameter, drill them out. This will leave the threaded shafts inside the stem, meaning that you'll need to buy a new one, but will at least allow the stem to be removed. There may be one or more spacers, washers of varying width, below (and sometimes, if the person who fitted the fork wasn't sufficiently skilled to cut the steerer tube or wanted to leave it long so it could be used on a different bike in the future, above) the stem. Remove them also.
With the stem removed, the dust cover should lift off. Place it on a rag on your work surface - when you remove the next piece, put it down to the right of the first piece and the third to the right of the second piece. That way, it's simple to get them back on in the correct order by moving from right to left. There may be a rubber seal under the dust cover, possibly the only seal or possibly the first of many (mountain bikes tend to have more). Due to the compression created when the top cap was fastened, the seal sometimes sticks to the top of the compression ring and cartridge bearing or upper top race. Peel it off if so and replace it if it tears while you do so.
The lower bearings will be sitting on the crown race of the fork (except loose bearings which are hopefully in the container with the towel). Remove them. Like the top and bottom races, the crown race will not need to be removed unless it's worn, in which case this can be achieved using a hammer and flat screwdriver - position the fork upside down in a vise using pieces of wood to protect the steerer from the jaws, then use the hammer and screwdriver to work around the lower surface of the race freeing it from the wider section at the base of the steerer.
While we're only winterproofing the headset rather than replacing it, it's not necessary to remove the races from the frame. However, we will give them a thorough cleaning which will reveal what sort of a state they're in - if they're badly born, it may be necessary to replace them. Removal is achieved using a specialist device known as a rocket tool, a tool used by most casual cyclists so infrequently that not many people bother to keep one in their tool box. Any decent mechanic will have one, so you may need to make a trip to the bike shop to get them taken out and new ones put in using another specialist tool called a bearing cup press. It's possible to perform both tasks using a hammer and metal rod (removal) and either a hammer and piece of wood or a home-made press (installation), but in both cases very slight misjudgement can ruin the frame, so this isn't recommended except for skilled home mechanics.
|Races - this is a crown race - should be smooth and
free of worn channels or pits. Any less than this and
they need to be replaced.
Clean all the parts thoroughly including the races in the frame, using any degreaser or a parts washer if you have one. Citrus-based degreasers are best as they will not corrode rubber seals as solvents can. A toothbrush will enable you to remove built-up grime and old, sticky grease. Once done, give them a wipe with a clean and lint-free rag.
Rather than sticking it all back together again, take the time for a quick inspection to ensure all parts are as they should be. Start with the races which should be free of pits and scratches. If badly worn, there may be circular channel running right around the inner surface or, in extreme cases, evidence of brinelling, deformation of the metal caused by an impact greater than the material's load limit. This is extremely rare in the case of road bikes - any impact great enough to cause brinelling is likely to have also snapped the frame - but is occasionally seen in BMXs, jump, freeride and downhill mountain bikes. Any of these will mean that the races need to be removed from the frame and replaced (see above) or, in the case of an integrated headset, the frame replaced (this being one of the drawbacks mentioned earlier and the reason that Chris King - headset genius - hates them).
Assuming the races are fine, check the crown race and the dust cover. These too should be free of wear. If the crown race is damaged, it will be necessary to remove and replace it. Removal is described above, replacement can be carried out in a similar way with the fork the correct way up in a vice provided very great care is taken to ensure the screwdriver contacts only the inner lip and not the polished race surface. The bearings themselves should be smooth and free of pits - in extreme cases, some will be missing and others cracked. Bearings are cheap, so consider replacing them even if they look to be in good shape as you won't be able to see microscopic damage that will develop into faults over time. All other parts should be in good shape without cracks or other obvious damage.
Lastly, check the steerer which should be free of rust, cracks and so on. Light rust can be removed with steel wool before protecting the metal with grease, heavier damage may require a new steerer - in a very few examples, the steerer can be removed from the fork yoke by loosening a series of allen bolts, but in most cases it will be heat-pressed in place (a process in which the yoke is heated so as to expand and/or the steerer cooled so as to shrink, the steerer then being inserted into the yoke and the fork returned to room temperature to lock them together). Carbon steerers are likely to have been bonded in place with adhesive. In all of the cases, the steerer can be removed but it's not a job that can be performed in the average home workshop and is best carried out by a skilled frame builder.
We'll now create extra seals at both ends of the head tube - and it's not going to cost you a penny. Simply cut two sections approximately 8cm in length from an old mountain bike inner tube (a road tube isn't wide enough) and roll them onto each end of the head tube so that the holes at both ends are free. Leave these in place.
Add a generous helping of grease to the crown race and the inner surface of the lower bearing race - this will be much easier to do if you have a proper grease gun. If you're using free bearings, turn the frame upside down and use grease to stick them in place inside the race as you reinsert the fork into the frame, but if using caged or cartridge bearings you can simply slide them over the steerer and back into place on the crown race, remembering to reinstall any rubber seals you took off when disassembling. Frequently, if loose bearings are used, there will be room for one extra to be added - this will decrease the load on each bearing, making the headset stronger and longer-lasting, at the cost of a miniscule increase in weight and friction. If you turned the frame upside down, turn it right way up again.
|A typical stem. The pinch bolts can be seen on the right
Unroll the sections of inner tube that you placed onto either end of the head tube earlier so that they completely cover the crown race, bottom race, bottom cup and upper race and top cap. Zip ties can then be used to tighten them below the crown race, above the bottom race and below the top race and below the stem, thus completely sealing the unit. Finally, if using a star nut or expansion device rather than the type of replacer with a bolt passing right through the steerer to a bottom cap, you can insert a rubber bung (widely available from shops selling home-brewing equipment such as larger chemists and some DIY/homeware stores) into the lower end of the steerer, completely sealing it to water and dirt.
(image credit: keithonearth
CC BY-SA 3.0)
Threadless quill headsets perform the same task as a threadless headset in a broadly similar way, but tension is provided by a locking nut rather than by a top cap as is the case with threadless systems. The stem is inserted into a shorter steerer tube and fastens in place with an expansion nut rather than bolting into a star nut. The advantages of this system are that handlebar height is more easily adjusted, disadvantages are that it's weaker and requires more specialist tools to disassemble.
First, loosen and remove the long bolt passing through the stem and into the steerer. Most bikes produced in the last 20 years will use an allen bolt - once again, usually 5mm - but some very cheap or old bikes will have one topped with a conventional hexagonal head, in which case a spanner will be required. If the bike has been correctly maintained, it will be possible to loosen it and then slide out the stem complete with the expansion nut; but if the bike has been neglected the nut often rusts into the steerer. If this has happened, use a metal rod or broom handle to push it out through the bottom - considerable force and a hammer may be needed. If so, the inside of the steerer is probably badly corroded and will need to be inspected - if it's really bad, it'll need to be replaced (and since most quill stems do not feature removable steerers, the fork will have to go too).
|The two types of threadless headset expansion nuts. On
the left, the wedge type which fastens by sliding against
the angled lower end of the stem and on the right, the
cone type that expands as it's drawn into the stem.
To begin, the lock nut needs to be removed. Several sizes have been used, but the majority will be the 32mm standard and can be removed with a dedicated headset spanner. They often seize, so use penetrating oil to free it if need be. Bikes with lock nuts in other sizes may need to be taken to the bike shop as few home mechanic kits have spanners large enough, though a big adjustable spanner can be used. Place the lock nut on a clean work surface.
Underneath will be a washer and, in the case of a rare high quality quill headset, a rubber seal. Remove both and place them in order to the right of the lock nut - that way, you'll know which order the parts need to be reinstalled. Below them is an adjustable race which will also need to be removed by unscrewing it from the steerer. This will reveal the bearings - as is the case with threadless headsets, they may be loose, caged or cartridge; but most will be loose. Remove them and add them to the other components. You can now remove the fork from the frame, catching loose bearings from the lower race in the container before placing the lower seal (if present) with the other parts.
Follow the same procedure described above for cleaning and inspection. As is the case with threadless systems, removal of the cups and crown race requires specialist tools or ingenuity and skill.
Reassembly is carried out in the same way as a threadless headset right up until the lock nut, once again using grease to stick bearings in place. Headsets of this type will also be afforded extra protection from winter conditions if seals made from an inner tube are used. Tighten the lock nut, check the forks for play and tighten more if necessary but not so much that the steering becomes stiff or grinds.
Finally, reinsert the stem into the steerer. The stem will have a minimum insertion mark etched into the metal - ensure that this mark is below the upper end of the steerer or it won't fix correctly into place and may come loose in use, causing a crash.
And there you have it. Next - the rest.