HEAD TUBE BEARINGS TUTORIAL
This basic tutorial will demonstrate the workings of a typical bicycle threaded head tube set, showing the removal and installation of the various components that make up a head tube set. Although there are slight size differences between different manufacturers, the basic principles of operation and assembly are virtually the same.
A bicycle head tube set consists of several bearing components that allow the forks to spin freely inside the head tube with minimal friction. These parts include: the head tube shell, a fork mounted bearing race, a pair of head tube cups, two ball bearings, a threaded bearing race, and several locking nuts and washers.
Electrical tape can also be used as a guide to mark off the end of the steel tubing, as long as you have a few points marked around the tube as a guide. Mark three or four points around the tube and then use the tape to connect the dots, creating a straight edge that can be used as a cutting guide.
The top locking nut keeps all of the underlying hardware secured on the threaded part of the fork stem (or steerer tube). This large nut also has an opening to match the inside diameter of the fork stem so that the gooseneck can be inserted snugly and locked down using its wedge system. The top nut is removed by turning it in a counter clockwise rotation using a large adjustable wrench. A pipe wrench can also be used, but be aware that the sharp teeth on a pipe wrench may scratch the flat surfaces on the lock nut. A large adjustable wrench is best.
Once the top nut as been turned a few times in the counter clockwise rotation using a wrench, it can usually be removed the rest of the way by hand. A very old bicycle may have some rust on the fork stem threads, so hand removal may not be possible. A very stubborn top nut may require holding the forks in place for leverage.
The top nut has very fine threads that will match those on the threaded fork stem (steerer tube). These threads are typically 24 TPI (threads per inch) and may extend 2 to 3 inches from the very top of the fork stem.
Under the top locking nut will be either a small washer or a reflector mounting plate. This washer will usually have an inside tab that will mate with a small slot cut into the fork stem to prevent it from spinning as you tighten the top nut. This locking washer allows the top nut to be tightened without altering the rotation of the hardware under the washer. This is the reason for the tab.
Under the locking washer will be a thin locking nut with several small tabs cut out around the edges. Like the top locking nut, once started the nut can be removed by turning it in a counter clockwise rotation by hand. If the nut is difficult to turn, it can be grabbed using a pipe wrench. Usually, another tabbed lock washer will be found under this locking nut, but this is not always the case.
The last and most important part of the top fork hardware will be the threaded bearing race, which creates a full bearing surface between its inside ridge and the head tube cup. The ball bearings ride on the ridge inside the threaded race, supporting the fork hardware in the top cup. This part will be easy to remove by hand on all but the most dirty or rusted forks. A pipe wrench can be used if the part is too difficult to turn by hand.
As you unthread the bearing race to expose the ball bearings, take note at the way they are inserted into the head tube cups. Bearings must be inserted correctly in order to function properly, especially those that include the retaining ring. The retaining ring is what holds the bearings all together in a circle. If your hardware does not include a retaining ring, then the bearings will be falling all over your workbench at this point.
The two ball bearings will be the same in diameter and usually include a retaining ring with a flat top. If your ball bearings look the ones shown here, then they are inserted into the head tube cups balls first so that the flat side of the retaining ring is visible. Another thing to note is that the lower head tube cup is usually slightly taller than the top cup. The reason for this is to keep water and dirt out of the bearings. The top bearing is protected by a lip on the threaded bearing race, so it has a shorter side.
The top fork set hardware will include a threaded bearing race, two tabbed locking washers, a thin locking nut, and the large top locking nut. In rare cases, the locking washers may not have inside tabs.
The lower bearing race carries most of the weight in the steering system, and it is mounted to the thickest part of the fork stem right at the base. All bearing race hardware is made of extremely hard steel, so it should not be struck with a hammer, or it may be chipped.
If you intend to modify the forks by cutting or welding, then it is advisable to remove the lower bearing race to protect it from damage. The race is friction fit to the fork stem. It can be removed by tapping it from the underside using a chipping hammer, chisel or steel rod. Work around the circumference using light blows until the bearing race is freed from the raised area where it is currently sitting.
The raised area that holds the bearing race is actually a very thin section of tube that has been spot welded or friction fit to the base of the fork stem. Not all forks have the same diameter tubing, so keep the race and other hardware with the fork it came from.
To remove the press fit bearing cups from the head tube shell, pound them out from the inside using a solid rod or heavy round tube, banging them around equally to remove them a little at a time. The bearing cups sit inside the head tube shell at a depth of about half an inch. Never strike the cups from the outside to remove them or they may be chipped.
Hardware store quality bicycles will have three distinct types of head tube ball bearings: one with a flat retaining ring as shown here, one with an angular retaining ring, or loose balls. The flat retaining ring style bearing is the most common type of ball bearing that you will find in a bicycle. They can be found in the head tube, bottom bracket, and hubs.
If you want to test the installation of the bearings, push down on the race and give it a turn. If the bearing is installed correctly, the friction will be very minimal no matter how hard you press. Try the bearing in the other way and then try the friction test. With the retaining ring rubbing on the race, the friction will be much increased.
The head tube bearing shown on the right is the most typical example of a bicycle ball bearing with an integrated retainer ring. This type of bearing is found in the head tube, bottom bracket, and wheel hub. The only difference in all three components will be the diameter of the bearing. The bearing shown on the right is always inserted balls first into the cup, with the flat side of the retaining ring facing upwards. The bearing on the left is a less common head tube bearing with an angled retainer ring. It is installed into the cup with the balls upwards.
Before re-assembling the fork hardware, clean the fork threads using a wire brush to remove any build-up of grease or dirt. Light rusting is fine, and can be taken off using some oil and a wire brush. Heavily damaged threads may be a problem, but often the installation of the threaded hardware can repair a thread much like a thread cutter.
The threaded bearing race is the same as the lower race, but it includes a weather cap and a place to grip while installing it on the threaded fork stem. Lubricate the race area where contact with the bearings will happen. You do not need to fill the entire void, as this is where the top edge of the head tube cup will be.
Once you have the threaded bearing race installed hand tight, give the forks a spin to see if there is excessive friction in the system. The forks will spin freely no matter how much you push or pull on them, but they should not seem difficult to turn. If the forks seem stiff, then most likely a bearing is installed backwards or you do not have a matches set of head tube hardware. There are several slight variances in cup and bearing diameter, and they need to be a matches set to function properly.
Once you have the threaded bearing race installed hand tight, add a lock washer so that the tab is fit into the groove cut in the fork stem. Some head tube sets may not include a lock washer over the threaded race, but it is highly recommended that you add one so that the installation of the remaining hardware will not affect the rotation of the threaded race. Lock washers create a friction buffer between threaded parts so that one does not affect the other. Once the lock washer is installed, add the thin locking nut, placing it on as tight as you can make it with your hands.
Head tube bearing hardware is a critical building block in almost every human powered vehicle you could make, and every one of our Downloadable Plans has one or more head tubes, even our tadpole trikes. Always salvage these bearing components from old bicycles, even if they are damaged. There will be some usable parts that can be used in your own homebuilt bikes.
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