Condensed Answer: The “Do Not Disassemble” label on a bottom bracket indicates that the model is not designed to be serviced. Instead, it should be replaced with a new one with equal parameters when the performance is no longer satisfactory.
Cartridge Bottom Brackets
Cartridge bottom brackets are models with sealed bottom bearings and a spindle integrated into them.
The sealed architecture is beneficial because it minimizes contamination. However, it also makes the bottom bracket non-serviceable, at least not easily, and requires the purchase of a new one periodically. Thankfully, cartridge bottom brackets are affordable.
Another downside of non-serviceable bottom brackets is that the user always has to search for a new unit that may not be available in the needed size.
Meanwhile, a serviceable bottom bracket can be used for a very long time provided that it’s serviced as needed.
One example of such a bottom bracket would be the old-school cup and cone model.
This is a non-sealed bottom bracket than can outlive the bike it’s on. Of course, it will be necessary to periodically disassemble it and re-grease the bearings. In some cases, it may also be necessary to replace them.
That said, even those bottom brackets aren’t internal. Eventually, the races of the bottom bracket (the surface against which the ball bearings slide) will wear down too and become uneven. When that happens the bottom bracket will start to wobble and will go through bearings very fast.
FAQ: Is it possible to service a sealed bottom bracket?
Technically, yes, although there isn’t an official method how to perform this operation as it’s not in the plans.
Cartridge bottom brackets can have sealed or loose bearings.
In the first case, it’s necessary to punch out the bearings and press-in new ones. If the bearings are loose, they do not have to be pressed out as one can gain access simply by removing the bottom bracket body.
Below are two videos showing how to disassemble a cartridge bottom bracket. The first deals with sealed bearings while the other showcases a model with free ball bearings.
The incentives to serve a cartridge bottom bracket are:
- inability to find a replacement bottom bracket (the pandemic made that a reality)
- exercise in bike maintenance
- cost savings (if you already have the tools needed to disassemble a cartridge bottom bracket, doing so can save you money).
The downsides of choosing this route are:
- frustration (a newbie may find this procedure unpleasant)
- money loss (the tools needed to service a bottom bracket may end up costing more than buying a couple of new ones)
FAQ: How often do I have to clean up a bottom bracket?
Below is a simple guideline indicating when a bottom bracket needs servicing:
- The bottom bracket has bearing play
When that happens the cranks will start to feel a bit loose. If the bottom bracket is serviceable, the play can be fixed by readjusting the cup and cone setting.
- The bottom bracket is hard to turn
If the bottom bracket becomes hard to turn, the most likely cause is contamination and worn or even broken bearings. In that case, the usual route is to replace the bottom bracket.
That said, if the bottom bracket uses a cup and cone mechanism there’s a chance that it’s simply too tight and needs readjustment.
Adjusting a cup and cone bottom bracket is tricky because the setting has to eliminate axle play while also allowing smooth rotation. Learning how to do this adjustment is a valuable skill as it translates to servicing common hubs too.
- The bottom bracket is creaking.
A creaking bottom bracket requires degreasing and re-greasing to eliminate the noise. That said, some models, especially the press-fit versions, are a lost cause and often creak even when new.
Bonus Tip: When cleaning your bike, do not use a powerful machine such as a pressure washer over areas that have bearings as the water from the hose will push the grease out and create an opportunity for contamination.
FAQ: Are the bearings of Shimano Hollowtech Bottom brackets serviceable?
Technically, the bearings of Hollowtech bottom brackets are sealed and therefore not the most convenient to service. Nonetheless, people have been disassembling and servicing them.
To reach the bearings, one has to remove a plastic seal and ring. Most of the time, that’s done slowly and carefully with a small flat head screwdriver. Once the bearings are exposed, they’re degreased with a solvent and re-greased. Then, the plastic covers are pushed back in.
This practice has the following downsides:
- Compromised Seals
Every removal and re-installation of the seals compromises them and creates an opportunity for dirt to infiltrate the bearings.
The material that the seals are made of is very brittle, and it’s totally possible to break them.