External bottom bracket replacement


Replacing an external bottom bracket on a bicycle involves removing the old unit and installing a new one. This process requires specific tools and knowledge to ensure a proper fit and functioning of the new bottom bracket. This comprehensive guide covers the necessary tools, steps, and tips to ensure a smooth and proper replacement of your bike’s external bottom bracket. Upgrade your ride with confidence.

Brief explanation of external bottom bracket

The external bottom bracket is a type of bicycle component that connects the crankset (the part of the bike that houses the chain rings) to the frame of the bike. It acts as a bearing system, allowing the crankset to rotate smoothly and efficiently. This design is lighter and stronger than traditional threaded bottom brackets, making it a popular choice for road, mountain, and gravel bikes. The external bottom bracket is also known for its easy installation and maintenance, making it a popular choice among cyclists.

external bottom bracket Shimano Hollowtech II
Is Shimano Hollowtech II bottom bracket and external bottom bracket this same thing?

External bottom bracket refers to a type of bottom bracket that sits outside of the bike frame, as opposed to an internal bottom bracket which sits inside the frame.
Shimano Hollowtech II is a specific type of external bottom bracket design by Shimano. It features a right hand crank arm with integrated bottom bracket axle and an outboard bottom bracket bearing system.
So, while all Shimano Hollowtech 2 bottom brackets are external bottom brackets, not all external bottom brackets are Shimano Hollowtech 2. There are other types of external bottom brackets that use different designs, such as SRAM GXP or FSA MegaExo.

If you’re not sure how to check if your bottom bracket is external o not, our article about different types of bottom brackets will help you to find out.

Importance of bottom bracket for a smooth ride

A smooth-running bottom bracket is crucial for a comfortable and efficient ride. It helps reduce friction, so you can pedal more smoothly and efficiently. This can result in less fatigue and improved performance, especially during long rides. A bottom bracket that is worn or damaged can cause a number of problems, such as grinding, creaking, or play, all of which can negatively impact your ride.

In addition to its functional benefits, an external bottom bracket also offers improved compatibility with different types of cranksets, which can make it easier to upgrade or replace parts. This can provide more options for customization and personalization, helping you to get the most out of your bike.

Overall, the external bottom bracket is an important component for ensuring a smooth and efficient ride. With proper maintenance and regular inspections, it can help keep your bike in top condition for years to come.

Reasons why you may need to replace your bottom bracket

There are several reasons why you may need to replace your bottom bracket, including:

  • Wear and Tear: Over time, the bearings in the bottom bracket can wear out and become damaged. This can result in a rough or inconsistent rotation, or even complete failure of the bottom bracket.
  • Noise: If you hear a grinding or creaking noise while riding, this could be a sign that your bottom bracket needs to be replaced. This noise can be caused by worn or damaged bearings, or by a loose or misaligned bottom bracket.
  • Play or Looseness: If you feel any play or looseness in your bottom bracket, this could indicate that the bearings are worn or damaged. This can cause the crankset to move around excessively, making it difficult to pedal smoothly and efficiently.
  • Upgrading: If you are upgrading your bike or changing components, you may need to replace your bottom bracket to ensure compatibility with the new parts.
  • Maintenance: Regular maintenance and inspections of your bottom bracket are important for preventing wear and damage. If you notice any signs of wear or damage, it may be necessary to replace the bottom bracket to maintain optimal performance.

How to Replace an external bottom bracket?

Tools required

To replace an external bottom bracket, you will need the following tools:

  • External bottom bracket tool. This tool is required to remove and refit the external cups
  • 5mm allen key. This is used to undo and tighten the bolts that hold the left crank in place.
  • Crank assembly tool. Required to remove and refit the crank arm fixing bolt.
  • Flat head screwdriver. Might be useful to the crank arm stopper plate.
  • Vernier calipers. Use this tool to measure the width of the bottom bracket shell.
  • Mallet. Helps to remove the crank axle from the bottom bracket.
  • Grease or anti-seize compound: This is used to lubricate the threads of the bottom bracket and prevent it from seizing up.
  • Clean rags or paper towels: Used to clean up any grease or debris from the bottom bracket shell.

It’s important to note that these are the basic tools you’ll need for a bottom bracket replacement. Depending on your specific setup, you may need additional tools or specialized tools to complete the job. It’s always best to consult the manufacturer’s instructions or seek guidance from a professional mechanic if you’re unsure about any part of the process.


  • Put the bike on a stand or turn it upside down
  • If you have a front derailleur then move the chain to the lowest gear and remove it from the cogs
  • Loosen the two clamp screws sequentially
  • Lift the stopper plate
  • Remove the crank arm fixing screw by undoing it anticlockwise

  • Remove the arm
  • Gently tap on the crank arm spindle until it moves
  • Remove the crankset

Removing an external bottom bracket

  • Fit the external bearing bottom bracket tool onto the bearing cup and unscrew it clockwise on the drive side and anticlockwise on the non-drive side
  • Make a note of any spacers on the bearing cups on each side
external bottom bracket spacers
  • Clean the bottom bracket shell threads with a rag or a paper towel
  • Apply a small amount of grease or anti-seize to the threads in the bottom bracket shell.
  • Clean the bottom bracket cups

Replacing an external bottom bracket

  • If you are replacing your external bottom bracket with a new one then make sure that it’s compatible with the brand of your crankset. We advise to use like for like replacement.
  • Some external bottom brackets are designed to work with either road or MTB cranksets. You should be able to find the information imprinted somewhere on the bottom bracket shell and on the box.
external bottom bracket for road or MTB
  • Measure the width of the bottom bracket shell. There are two external bottom bracket standards: 68mm/73mm and 83mm. Make sure that you have the correct size replacement
External bottom bracket measurements
  • Fit the spacers on the bearing cups as noted earlier and fit the sleeve on the right hand side cup.
  • Fit the right hand external cup into the shell and screw it slightly by hand anticlockwise.
right external bottom bracket screws in anticlockwise
  • Fit the external bearing bottom bracket tool onto the bearing cup and screw it anticlockwise until it stops.
tightening an external bottom bracket with a tool
  • Now fit the left hand side external cup into the shell and screw it slightly by hand clockwise.
left external bottom bracket cup screws in clockwise
  • Fit the external bearing bottom bracket tool onto the bearing cup and screw it clockwise until it stops.
tightening left external bottom bracket cup
  • Once the bottom bracket is in place slide the crank’s axle through the bottom bracket hole. Make sure that it’s all the way in.
Fittin crankset through external bottom bracket
  • Place the chain on the front chainring.
  • Refit the left crank arm. If you’re not sure how to do this we have a great article here to guide you through the task.

Now, that you have replaced your external bottom bracket you can again enjoy noise and play free, smooth ride on the road or the trail.

Support us by becoming our patron so we can keep creating cycle maintenance related articles and videos.

Click here to find out more.

Leave a Comment