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Servicing Bicycle Headsets

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Sheldon Brown photo
by Sheldon "Steering" Brown
revised by John "Balanced" Allen
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Also see the Headset entry in my Bicycle Glossary and my Article on Handlebar Height.

 Headset anatomy

The "headset" is the bearing assembly that connects the front fork to the frame, and permits the fork to turn for steering and balancing.

A headset consists of four races plus associated parts -- from top to bottom:

  1. The adjustable race attaches to the steerer.
  2. The upper head race is pressed into the top of the head tube.
  3. The lower head race is pressed into the bottom of the head tube.
  4. The crown race is pressed on to the bottom of the steerer, just above the crown.

"Pressed" means that the parts are attached using an interference fit between cylindrical surfaces. The inside diameter of the outer part (head tube, crown race), is very slightly smaller than the outer diameter of the part which mates with it (head race, fork crown race seat. Force must be used to assemble (or disassemble) them. When assembled they act as a single part.

There are two common headset types: threaded and threadless.

Threaded Headset

Note wrench flats on locknut
and top threaded race.
Threaded Headset

Threadless Headset

Note pinch bolts on stem.
and no wrench flats.
Threadless Headset

 

Most bicycle frames don't care which style headset is used, as long as it is the correct size. For any given frame, you can usually switch back and forth between threaded and threadless by changing:

 

Sizes

The nominal size of all headsets is based on the outside diameter of the fork steerer. This is a source of confusion, because the steerer is not visible on an assembled bicycle. The steerer is enclosed inside the frame's head tube.

Threaded Sizing

In the case of a bicycle with a traditional quill/expander/wedge type stem, the stem shaft will be 1/8" smaller than the steerer. Sometimes people measure the stem diameter and assume, incorrectly, that this is the size headset they have.

The vast majority of bikes with threaded headsets use the 1 inch size. A sizable minority uses the 1 1/8 inch size. Other sizes are generally quite rare. The illustrations below show how to tell the 1 inch size from the 1 1/8 inch size:

1 Inch threaded headset
(common traditional size)

(7/8" Quill is noticeably smaller
than a U.S. Quarter)

1 Inch Threaded

1 1/8 Inch threaded headset
(rare size, mostly 1990s bikes)

(1" Quill is a teeny bit larger
than a U.S. Quarter)

1 1/8 Inch Threaded

Other Dimensions

Other dimensions also matter when selecting a replacement headset.

Unless you are very sure about all of these dimensions, take the old headset and/or the frame and fork with you when you go to buy a new headset. Common dimensions are shown in the tables below. Better bike shops can mill a fork for a smaller crown-race press-fit diameter.

Threaded Headsets

Size
Steerer O.D.
Stem diameter
Steerer I.D.
Crown race
Inside diameter
Frame Cup
Outside Diameter
Threads
Per inch
Notes
BMX/O.P.C. bikes .833"
(21.15 mm)
26.4 mm 32.7 mm 24 Used mainly on bicycles with one-piece cranks, also some early mountain bikes.
French 25 mm 22 mm 26.5 mm,
27.0 mm
30.2 mm 25.4
(1 mm)
Obsolete. French steerers usually have a flat filed on the back, rather than a grooved keyway as with other threaded systems. The bottom headset parts wear faster;, you can replace them with ISO parts can use the old top headset.
1" ISO Standard
(25.4 mm)
7/8"(22.2 mm) 26.4 mm 30.2 mm 24 This is the standard 1" size.
1" Italian (25.4 mm) 7/8"(22.2 mm) 26.5 mm,
27.0 mm
30.2 mm 24 Obsolete. Threads are cut at 55 degrees, but an ISO or J.I.S. top headset can be used. Note possible difference in crown race press-fit diameter.
1" J.I.S.
(25.4 mm)
7/8"(22.2 mm) 27.0 mm 30.0 mm 24 Older or lower-quality bicycles from Asia
1" Raleigh
(25.4 mm)
7/8"(22.2 mm) 26.4 mm 30.2 mm 26 Proprietary size used on Raleighs made in Nottingham, England
Austrian
(26 mm)
22 mm 26.7 mm 30.8 mm 25.4
(1 mm)
Higher quality Austrian bikes use English/ISO
French Tandem 28 mm 22 mm 25.4
(1 mm)
Obsolete and rare.
1 1/8" (28.6 mm) 1" (25.4 mm) 30.0 mm 34.0 mm 26 "Oversized" (This size is more often used for threadless systems.)
1 1/4" (31.8 mm) 1 1/8" (28.6 mm) 33.0 mm 37.0 mm 26 Mainly used on tandems

 

Threadless Headsets

Size/Stem diameter
Steerer O.D.
Crown race
Inside diameter
Frame Cup
Outside Diameter
Notes
BMX/O.P.C 26.4 mm 32.7 mm Used mainly on bicycles with one-piece cranks.
1" ISO Standard (25.4 mm) 26.4 mm 30.2 mm This is the standard 1" size.
1 1/8" (28.6 mm) 30.0 mm 34.0 mm Most newer mountain bikes use this size.
1 1/4" (31.8 mm) 33.0 mm 37.0 mm Mainly used on tandems
1.5" (38.1 mm) 39.8 mm 49.6 mm OnePointFive standard for downhill and freeride applications.

Troubleshooting

Symptoms:

Shakiness

Shakiness indicates that the headset is adjusted too loose. The easiest way to check for this is to apply the front brake and push the handlebars back and forth, front to back. If you feel a "clunk" it usually means the headset is too loose. You can determine that the looseness is in the headset and not the brake by resting a finger across the gap between the races of the top or bottom headset assembly. If the bicycle is in the workstand with the front wheel off, you can just push and pull on the forkends.

Stiffness

Stiffness results when the headset is adjusted too tight. Check for this by lifting the front of the frame so that the front wheel comes off the ground. Normally, the wheel and handlebar will flop to one side or the other by their own weight when you do this. If the front wheel and handlebars are off the bicycle and you turn the fork, you may feel a light, smooth, even drag from bearing seals -- this is normal. Roughness or uneven drag indicate problems.

Shakiness AND Stiffness

Sometimes you will find both of these faults at the same time. This indicates a more serious problem, not just an adjustment issue. You may find that the headset is loose when the fork is facing straight forward, but gets tight when you turn the handlebars to one side or the other, or that it simply can't be adjusted. Possible causes:

"Indexed Steering" ("Brinelling")

All of the other ball bearings on a bike spend their lives rotating round and round, but headsets spend most of their time pointing straight ahead. Sometimes you will see that the bearing balls have created a neat row of little dents in the bearing surface of the lower frame cup and/or the crown race. This creates the effect commonly known as "indexed steering" where the balls sort of "snap" into place, and the fork tends to stick in the straight-forward position.

brinell led

A "Brinelled" crown race (larger than actual size)

The dents in the races resemble the dents created by the Brinell hardness test procedure, and as a result, this type of damage is sometimes called "Brinelling." This is a bit of a misnomer, because the Brinell hardness test involves basically hammering a bearing ball into a metal sample with one good hard whack. Some folks assume that the dents in headset races also result from impact, but actually that is not commonly the case. Instead, it has to do with lubricant breakdown. Jobst Brandt has an article on this site describing the process in detail.

Ideally, a "Brinelled" headset should be replaced, but you can often cure the problem by replacing the retainer with loose balls. You use the same size balls, but can usually fit more of them into the races if you leave the retainer out. As a result, the greater number of balls, closer together, no longer all line up with the dimples in the races.

A headset race can, on the other hand, become indented due to overload in a crash. The dents then will be deeper in the part of the way around the race that took the impact. Usually, in this case, the fork will be bent too. The indented race(s) and the fork need to be replaced.

Adjustment

The adjustable race is secured by either a:

Adjustment (Threaded)

Adjustment is easiest if you use two wrenches. You may use large end wrenches, or special wrenches made to fit the wrench flats of the locknut and top race -- but in a pinch, you can get by with a single large adjustable wrench. There is some risk of stripping out the tab of the keyed washer or of its damaging the threads of the steerer if you use a single wrench.

  1. Leave the bicycle right-side-up with the front wheel resting on the floor.
  2. Loosen the locknut. Preferably, hold the top race from turning with one wrench while turning the locknut with another. If using one wrench and the top race starts to turn along with the locknut more than a tiny bit, go looking for a second wrench.
  3. (Skip this step if threads and washer are greased.) Unless the threads and keyed washer are already greased, remove the locknut and keyed washer. Do not unscrew the top race, unless you are going to go to overhaul the headset -- loose bearing balls might fall out.
  4. (Skip this step if threads and washer are greased.) Grease the keyed washer and the threads of the steerer.
  5. (Skip this step if threads and washer are greased.) Replace the keyed washer, and screw the locknut down most of the way, leaving it loose..
  6. By hand, without using a wrench, screw down the upper head race until the bearings just begin to bind, then back it off about 1/8 turn. (Tightening the locknut will press down the upper head race, due to its slight looseness on the threads.)
  7. Tighten the locknut lightly and test the bearings for free rotation with no excess play. Unless the adjustment is perfect, loosen the locknut and readjust the bearings as necessary. When the adjustment is correct, tighten the locknut fully and check again.

Older French threaded headsets use a serrated or pinned keyed washer which mates with the upper head race. With these headsets, you must back off the locknut farther so that you can rotate the upper head race.

Adjustment (Threadless)

Threadless headsets have an adjustable race that slips over an un-threaded steerer. There are three distinctstarnut types of threadless headsets which adjust differently:

 

Overhaul

Headsets are pretty durable, and hardly ever need to be serviced if your bicycle has a front fender.

If you ride without a front fender in wet conditions, the front tire will spray filthy, gritty water right up into the lower race. (It is the lower race that supports your weight. Most headset failures occur at the lower race.)

To overhaul a headset, you first have to remove the stem. It usually also makes things easier if you remove the front fender, wheel and brake, or at least disconnect the front brake cable.

If you have a cyclecomputer pickup mounted on the fork, you'll also need to remove one end or the other of the computer wiring.

It helps also to turn the bike upside down once the stem has been removed -- easier with a workstand. Don't rest old upward-arched drop-bar brake cables on the floor.

Once you have the fork out of the frame, you can see what kind of bearings the headset uses. The illustrations below show the assembly order for typical headsets with different types of bearings. A headset may or may not have contact-type seals as shown under the lower bearing of the headset at the left.

This threaded headset has bearing balls in cages (retainers), though generic loose bearing balls can be installed as replacements in most headsets which were supplied originally with retainers. This threadless headset has cartridge bearings. Only exact replacement cartridges will work. Cartridge bearings are mostly to be found in newer, threadless headsets.
382px-Bicycle_headset_exploded_view Bicycle_headset_(threadless)_exploded_view
Images by keithonearth on Wikimedia Commons, reproduced under Gnu free documentation license

Once you have removed the fork, you can check the condition of cartridge bearings by turning them with your fingers. They should turn smoothly, though there will usually be some drag from bearing seals. Exact replacement is needed with cartridge bearings -- or else, replace the entire headset.

After cleaning a headset that uses retainers or loose bearing balls, check the bearing races for indentations and pitting.

If the headset uses bearing balls held in retainers, you could re-use them if they are still in good condition too. There's little standardization among different makes/models of headsets, so finding a replacement retainer may be difficult or impossible. The top and bottom retainer are usually identical, and exchanging them will increase wear life. It may be possible to pop the old bearing balls out of a retainer and insert new ones, taking care not to bend the retainer. You can increase the load capacity and wear life by replacing retainers (especially the bottom one) with loose bearing balls, though in some cases it's difficult to keep loose balls in place during reassembly.

If the headset had loose bearing balls, replace them...they're cheap enough! You very likely lost some anyway when you disassembled the headset. Most headsets use either the 5/32" or 3/16" size.

For re-assembly, it is very helpful to have the bike mounted upside down in a work stand.

If you lower the steerer partway into the head tube, you will be able to load up the bottom (but facing upward) head tube race with bearing balls without worrying about having them fall down through the head tube, because the steerer will fill the gap. Use enough grease to hold the bearing balls in place. Leave the race one ball short of full, so the balls won't jam up against each other when you reassemble the headset. Once all the bearing balls are in place, add lots more grease, to help seal out dirt when the bicycle is in use.

Once the balls are in place for the lower part of the headset, you can drop the fork down the rest of the way into the headset.

Grease the inside of the upper race, and get it started onto the steerer. Load it up with balls, add more grease, then slide (threadless) or screw (threaded) it "up" to take up most of the slack in the system, so the balls can't fall out.

For a threaded system, you can then turn the bike right-side up to complete assembly/adjustment and wipe off the excess grease.

For a threadless system, you need to secure the fork before turning the bike right-side up. I sometimes use an old toe strap for this, tying the fork crown to the down tube of the frame.  

Replacement/Installation

Removing and re-installing the headset bearing races is not necessary for a normal overhaul, only when you are replacing the headset or installing a new fork.

If you are working with an inexpensive all-steel headset, you can often manage with basic hand tools, but if your headset has aluminum or plastic parts, you really need specialized tools made for the purpose. These tools are generally not economical for a home mechanic to purchase, given how rarely they are likely to be used.

The following assumes you're working with an all-steel headset:

Removal:

The races can usually be removed with a hammer and an old flat-blade screwdriver that you don't care about.

The head tube races usually come out pretty easily if you stick the old screwdriver down into the head tube until it hits the internal edge of the race. Tap gently once, then move the screwdriver to the opposite side of the head tube. Keep going back and forth every other blow, so that you won't be driving the race out crooked, which could damage the head tube.

The fork crown race is sometimes more challenging, depending on the construction of the fork crown and the width of the race. You may or may not be able to get a good purchase on the underside of the race.

If the race has a good overhang on both sides of the fork crown, a bench vise is often best for this. Open the vise just wide enough to permit the fork crown to fit through loosely, so that the crown race is sitting on top of the vise jaws. Use a mallet to rap on the top of the steerer, driving the fork down and away from the race. It is a good idea to thread the headset locknut onto the steerer before doing this, to prevent damage to the threads of the steerer.

Alternatively, a bicycle workstand can be used to clamp the steerer with the fork upside down. You can use the hammer and old screwdriver to drive off the race.

Some races and some fork crowns give very little to grab onto. There are special shop tools to work around this problem, so you might want to just bring the fork into your local shop and have it remove the race.

Replacement:

The press-fit races need to be seated firmly.

The head tube races can be tapped into place with a mallet and a block of soft wood that spreads the impact all the way around the margin. Use another block of wood to support the other end of the head tube, and be sure it's sitting level so you don't damage it. Bike shops have threaded tools to pull the races into place.

The fork crown race is more difficult to seat. You can tap on one side and the other, inboard next to the steerer with your old screwdriver, or you may tap on a length of pipe that just fits over the steerer. Turn the pipe around as you tap, in case the surface which rests against the crown race isn't perfectly level.

If you don't get the races firmly seated, they will seat themselves during riding, and the headset will loosen. It then only needs to be readjusted. If working on someone else's bicycle, you should be sure to get the races seated fully before delivering it. If you don't have special tools, you could go for a short, bumpy ride to seat the races, then readjust the headset.

Also see my Adventure Cyclist article about headsets.

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2010, 2011 John Allen
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