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Adjusting Radial Cartridge Bearings
Technically, radial cartridge bearings are not adjustable, but they can be installed so they are not functioning properly. Very few bike mechanics understand how radial bearing systems work. The purpose of this article is to give you that understanding and tell you how to adjust them.
The image above shows a rear hub with four bearings. Each bearing has an upper race, a lower race, ball bearings, and seals. They are manufactured so that there is a very small amount of play. This is important because it allows the bearings to run freely.
They are installed in the hub and cassette with the upper or outer race being a press fit and the inner or lower race being a slip fit. When they are pressed in, it is possible to press them in either too much or too little since they are pressed in until they “seat” against the bearing bore. It is also possible that the tolerances in hub, cassette body, axle, or spacers are a little off.
They hub system is designed so that the end caps, inner bearing races, axle and spacers are pressed together when you tighten the end caps. If the inner or bottom bearing races are not aligned with the upper pressed fit races, the bearings will bind or be too tight. The best way to adjust them is to add a spacer to the end of the axle. That spacer will allow the inner race to flow a little. Another option is to Loctite the end cap while it is slightly loose. The easiest way to create a space is with a very thin wire wrapped around a pencil or something similar. You want to create a circle so there is clearance for an axle.
Front hub bearing systems work the same way except there are only two bearings but adjusting them is the same process.
If the hub is too loose, one or more of the bearings needs to be pressed in further. When pressing in bearings, just press until you feel the bearing bottom out. If you press them in further you are probably seating them too deeply.
Even though radial cartridge bearings have a slight amount of play often you can’t feel it because the contact seals on the bearings prevent you from feeling it. On bearings with very light not non contact seals (like ceramics) you often can feel it more because of the lack of contact in the seals.