BICYCLE BEARING BASICS TUTORIAL
This basic tutorial will demonstrate how to remove, grease, and assemble bicycle ball bearings. Although the bearings in a bicycle vary in size from component to component, the installation and maintenance are the same. The following steps will use the ball bearings from the head tube and bottom bracket as an example. Wheel hub bearings are also the same, although smaller in diameter.
When you are disassembling bicycle bearings, take note of the orientation of the bearings into the cups. Typically, the balls are inserted into the cups with the flat part of the retaining ring facing upwards, but this is not always the case.
An obvious indicator of improperly installed bearings is excessive friction. If you place the bearing into the cup and press down on the race, it should turn freely no matter how much pressure you apply. A bearing installed upside down will have a lot of friction and be difficult to turn while pressing down on the moving parts.
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 and 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, and it is installed into the cup with the balls upwards.
This less common type of head tube bearing with an angled retaining ring is installed into the head tube cup so that the balls are facing upwards. If unsure, simply try the bearing both ways while you press and turn the race hardware to see which way offers minimal friction.
Since bicycle ball bearings are very low speed and torque bearings, typical axle grease from a hardware store is all you need when regreasing them. Axle grease will come in a round cylinder that is made to fit into a caulking gun, but will be applied manually when used for bicycle bearings.
To re-grease the two bearing sin the head tube, ensure that all components are cleaned of the old grease and any dirt and then begin by applying a ring of grease with your finger around the fork crown bearing race.
Next, apply the grease to the inside of the bearings so that it fills the gaps between the balls in the retaining ring. This is again done by dipping your finger in the grease.
Install the lower fork bearing onto the fork crown race, keeping in mind that the balls will be facing upwards so that they end up inserted into the cup. The exception to this rule is the less common head tube bearing having the angular retaining ring.
Once the lower bearing, race, and cup have been lubricated, insert the fork into the head tube and then press down on the parts to check for friction. If the head tube and fork do not turn with minimal friction, check the orientation of the bearing.
Lubricate the top bearing and cup in the same manner, filling the gaps in the retaining ring with grease. Run a small bead of grease into the head tube cup as well, ensuring all moving parts are well lubricated.
The threaded bearing race that screws onto the fork thread also gets a bead of grease placed along the ring using your finger. Only the part of the ring that will press into the bearing needs the grease.
Thread on the bearing race so that it is about as tight as you can make it using two fingers. The bearing race should never be over tightened, just tight enough to remove all play and add a little resistance.
With the bearings installed and the top threaded race hand tight, give the forks a spin to see if they turn around with minimal friction. Although the forks will not spin around more than once, they should do so freely, no matter how hard you press them into the head tube. If the forks seem stiff to the point that they are difficult to turn, then you either have a bearing installed in reverse or have a mismatched head tube set. There are several sizes of bearing, cups, and races, and they must all belong to a set.
The bottom bracket also contains a pair of similar ball bearings, although they have larger balls and a small number than the head tube bearings. The bottom bracket bearings carry the crank axle and will have to endure the entire weight of the rider and all of the pedaling forces delivered to the crank arms.
Bottom bracket bearing hardware is much the same as head tube hardware but instead of a threaded race, the bottom bracket had threaded bearing cups. These two threaded bearing cups also have a right and left side and include forward and reversed threads, so it is important to know which way to turn the cups on each side of the bottom bracket. The cup on the left side is a standard thread, so it is removed by turning it in the counter clockwise direction. This cup also includes a locking ring that can be removed by hand once it is initially set free with a pipe wrench or by tapping it into one of the small notches. With the locking ring removed, a small wrench can be used to unscrew the bearing cup by catching it in the flat area and turning it counter clockwise until it is free from the bottom bracket shell.
The right side bottom bracket bearing cup has reversed threads so it is taken out by turning it in the clockwise direction. I recommend you do not remove this cup as it can be very difficult to unthread and makes it easy to cross thread the bottom bracket later on by placing the wrong cup in the wrong side. You can easily clean and grease the bearings from inside the bottom bracket, so there is no real need to remove this cup unless it is obviously damaged.
Another thing to note that may not be obvious is that one side of the crank axle is longer than the other as it extends past the bearing race. The longer side of the axle is made to take the chain ring side of the crank set, which needs more clearance from the frame than the bare crank arm. The long side of the axle is placed on the right side of the bike.
Having such fine threads, it may take a few tries to get the bearing cups to begin threading into the bottom bracket shell. Never force the bearing cups to turn with a wrench or you may permanently damage the bottom bracket shell by cross threading it on the inside. If you find it very difficult to thread in the bearing cups then try cleaning the threads once again and make sure you have the correct cup for the correct side of the bottom bracket. Remember those right and left side threads.
Remember that the balls go into the cups so that the flat part of the retaining ring is visible. Installing the bearing in reverse will result in excessive friction and cause the bearing parts to fail. If your ball bearings did not include a retaining ring, simply place them into the grease around the bottom bracket cup.
After you have all of the cups installed hand tight, spin the crank axle to ensure that it turns with minimal friction and no play. Bearing cups only need to be tightened enough to remove all play in the bearing parts and to create a minimal amount of resistance. As bearing surfaces wear, some readjustment of the cups will be necessary.
When you are salvaging bicycle components that include ball bearings, it is advisable to completely clean a de-grease the bearings and wear parts so that you can determine if any of them need to be replaced. It's often difficult to identify a bad bearing when it is packed in grease, and many times it may only be the grease that is rusty looking, not the bearing.
A bearing that is obviously rusted or balls that have lost their shine need to be replaced. If you run a rusty bearing, it will eventually destroy the bearing race, wearing a groove into the hard surface. If only one or two balls are rusted, you could replace them, but chances are the damage will be even throughout the entire bearing. Also, check bearing cups for rust or cracks that can develop over time from heavy use. Cracked bearing cups need to be replaced, but some amount of rust may be removed using steel wool inside the bearing cups. Each year of service, you should check your bicycles bearings for wear and give them a fresh coat of grease.
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