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Most modern cranksets can be dismantled easily and without special equipment. However, the bearings themselves should only be accessed with knowledge and the right tools.
The necessary tools
- Hexagon socket (left) or Torx spanner: to dismantle the components and access the bearings; the bearing play is also usually adjusted using Allen keys.
- Shimano crank tool: to fit Shimano cranks. Here is the professional version made of metal, the inexpensive plastic version is also suitable for occasional tinkerers.
- Press-in tool: Universal variants that are suitable for different bearings are good (left-hand tool). The shells of classic, non-integrated headsets can also be pressed in. For the occasional installation of pressed bottom brackets, such as press-fit bearings, simpler variants are sufficient (right).
- Knock-out toolDepending on the bearing size, this is important for removing pressed bottom brackets. The tools are pushed through the inside of the bearing, which is then driven out from the opposite side with targeted hammer blows.
- Nut for threaded bottom brackets: Threaded bearings absolutely need the right tool, and there are many variants. Important: The tool must fit snugly, otherwise it will slip off.
- Hammer (left) and Soft-face mallet (right): The cranks in particular can sometimes get stuck, and a hammer is also required when removing pressed bearings. Only work directly on the components with a soft-face mallet!
Special features of the crank manufacturers
Shimano: The cover screw in the left-hand crank only secures the position of the crank on the axle. Therefore, only tighten the screw lightly with 1 to 2 Newton metres. Then secure the crank with the Allen screws. Tighten these alternately and evenly so that the crank does not tilt.
SRAM: SRAM cranks are removed with an integrated puller. The crank can be extremely tight and disassembly can require a lot of force! With many SRAM bearings, the bearing play must also be adjusted. This is done with a screwed ring on the left-hand side, which is fixed in the correct setting with a small Allen screw.
Campagnolo: On high-quality Campagnolo cranks, the two axle halves are bolted in the centre; you can reach the bolt with a long Allen key. Be careful with Super Record cranks with a titanium axle: the bolt has a left-hand thread! You can recognise this version by the printed red ring around the axle. The bearings are pressed onto the axle halves and special tools are required to replace them. A visit to the dealer is recommended here.
Recognising wear on the bottom bracket
Because bottom brackets have to absorb a lot of load and are exposed to dirt and water when riding in the rain, defects are not uncommon. Wear is often signalled by irregular cracking noises. If the crank already has play, turns sluggishly, jerkily or makes grinding noises, it is high time to replace the bearings.
Cracking noises can also be caused by worn bearing seats; the noise usually occurs during operation at the point of maximum load (crank horizontal): Even perfectly good bearings or bearing shells are then no longer firmly seated in the frame. Carbon housings are particularly susceptible to this. You can try to lubricate the bearings with some assembly paste, but this is usually only a temporary solution. Specialised carbon repair companies can help in difficult cases.
The right tool
Make sure you know which type of bottom bracket is installed in your frame and only work with the right tool: You can recognise classic bearings that are screwed into the frame by the external tool holder. Pay attention to the correct direction of rotation of the thread, which is often marked on the bearing shell. When fitting the bearing, it must be easy to screw in the first few threads by hand. Only use the bearing spanner for tightening! Otherwise there is a high risk of damaging the threads (and thus the frame).
For bearings pressed into the frame (press fit), use a special knock-out tool to prevent the bearing shells from tilting and damaging the seats in the frame. The new bearing should be fitted using a suitable press-fit tool.
Bearings pressed directly into the frame without bearing shells (e.g. BB30) can hardly be removed without destroying them. However, it is important to use a suitable knock-out tool so that the seats in the frame are not damaged.
Clean and lubricate bottom bracket
Important for all bearing types: Clean the bearing housing thoroughly! Dirt can damage the sensitive threads; in the case of pressed models, the bearings may tilt or not align perfectly. Apply a little grease to the threads or bearing seats to make assembly easier. A thin layer of grease on the outer sealing ring prevents moisture from penetrating.
Professional tips
- Dismantling the crank and bottom bracket often requires a lot of force. To protect the frame and parts, you should not carry out such work on the assembly stand. It is better to place the bike on the ground and, if possible, ask someone to hold the frame or the tool while you dismantle it.
- Before removing the chain, place it on the large chainring so that you do not injure yourself so easily on the sharp teeth.
- If cranks have not been dismantled for a long time, they may be very tight on the shaft. Spray some oil in the area of the screw connection and in the gap between the crank and frame. This will loosen corrosion and make it easier to unscrew.
Jens Klötzer
Editor
