SERVICE A THREADED BOTTOM BRACKET
The bottom bracket (BB) comprises three parts – two external cups, each containing a bearing, and an internal plastic tube, which is held in place once the cups are threaded into the frame. Markings on each cup show the make/model of BB and which side of the bike it should go on.
Dierent BBs require dierent tools (eg. SRAM and Shimano’s aren’t cross-compatible), so you may need to check the manufacturer’s tech documents to work out which you need. Press the tool squarely onto the non-driveside cup and give it a few turns towards the front of the bike (anticlockwise).
If you’re reusing the original cups, make sure any spacers are still installed. For new cups of the same style, simply copy the previous set-up. If you’re unsure about the spacers required for your frame/ crank combination, check the manufacturer’s tech documentation for details.
Thread the driveside cup (with internal plastic tube attached) into the BB shell, turning it towards the rear of the bike (anticlockwise). Use the BB tool to tighten it until it’s securely in place.
Place your finger on the inner lip of one cup and rotate the bearing. If it runs smoothly, that cup is fine to keep using and you just need to add some fresh grease to the BB. However, if one or both bearings feel gritty, then it’s time to replace them. Either way, you’ll need to remove the cups.
With the non-driveside cup loosened, remove the driveside cup – again, turning it towards the front of the bike (clockwise). Then, fully undo the non-driveside cup. Check the threads within the frame and use a rag to clean them. It’s not unusual for the BB shell to have water/dirt inside it.
Add fresh grease to the threads inside the BB shell and on the outside of the cups. Thread the non-driveside cup in halfway, by hand, turning it towards the back of the bike (clockwise) and being careful not to cross-thread it. It will now act as a preload cap for the driveside cup.
To finish, tighten the non-driveside cup, then refit the cranks. If you’re worried about how tight to do up the cups, they require approximately 40Nm of torque – ie. all the eort you can muster!