by Nick Di Cristofaro
The bottom bracket (BB) is where your engine, legs that is, connects and transmits force to propel your bike forward. Every bicycle has a BB. The part often seems surrounded in confusion because of different types (and the litany of noises and creaks that come from them). There are two basic types of BB on modern bicycles: threaded and press-fit. A threaded bottom bracket is the older system (and more reliable, in my opinion) with bearings contained inside threaded cups that are screwed into the frame. The bearings themselves sit outside of the frame. A press-fit bottom bracket’s bearings are fitted into a frame either directly or into cups that are pressed into the frame. Here are some tips and basic maintenance you can do at home to prevent costly failures down the road.
I recommend a full overhaul of the BB at least once or twice a year on your road bike and more often on a mountain, gravel or cyclocross bike, depending on the conditions you ride in. If you have ridden in a major downpour, then it’s a good idea to, at the very least, remove your crank, inspect the bearings, and clean and grease the seals.
The basic clean
Make sure you are familiar with the removal process of your particular brand of crank. Once removed, clean the shaft and chainrings with degreaser and inspect the chainrings. Now would be a good time to replace them if they are worn. Remove bearing seals if it’s possible. Rotate the inner race of the bearing on each side with your hand. If the bearings feel gritty or are hard to turn, then the bearings, and possibly the cups, too, will have to be removed for further servicing. If the bearings feel fine, then inspect the inside of the BB shell and clean out any moisture, dirt and old grease. Apply grease to the outside of the bearings and a light amount on the crank shaft itself before reinstallation. Make sure to reinstall any appropriate washers and spacers in the order they were removed. Tighten any bolts to spec. Give the crank a spin by hand without the chain on the rings to check for smoothness. One final step is to check for play by grabbing the crank arms and rocking them back and forth.
Working on the bearings
If, during the basic cleaning, you noticed the bearings are in need of servicing or replacement, then you’ll have to remove them. If you don’t have the tools you need, take your bike to a good shop.
A threaded BB’s cups are usually removed and replaced as a unit. Some brands have serviceable bearings. Make sure you do your research on your model. If you have a press-fit BB, you’ll have to take the bearings out of the frame. There are special tools available for specific types, such as one-piece press-fit BBs and two-piece BBs that are threaded to each other. Make sure you know what BB you have before you start the process.
If your bike has a press-fit BB with two separate pieces, you can use a large-face aluminum (or other soft metal) drift punch to knock out the bearings/cups. You must take care to ensure that you strike the inside of the bearing/cup and not the frame itself, which will get gouged. Work around the perimeter of each bearing/cup to knock out the assembly evenly. As you hit it with the punch, you should start to feel movement as the assembly moves outward. After you’ve removed the bearings, clean the BB shell. Before you install new bearing/cups, grease the outer race of each. If the removal process was super easy, I recommend using a bearing-retaining compound instead of grease, which provides extra holding strength. The compound might help to prevent future noises and creaks.
Finally, install the bearings using an appropriate bearing press. This press adds an even amount of force to the outside race of the bearings. Note: never press on the inside race of any bearing during installation as it will ruin, or even possibly break, the inner race loose from the outer race. Once you have your new BB in place, you can reinstall your crank and get pedalling.