The following post will help you replace the newer, external, type of bottom bracket. I’m showing a Shimano XT bottom bracket. Shimano and Raceface are typically interchangeable; however, FSA and Truvative are NOT. It is best to keep with the same brand just to be sure.

Just to be clear, for this example I’ll be replacing a Shimano bottom bracket.

You will require the following set of tools to begin the replacement of your bottom bracket:

• 5mm Allen key
• Flat bladed screw driver
• BB tool with ability to remove the end caps/adjustment cap
• Hammer (tap-o-matic 3000 or higher)

Now that you are ready to begin, loosen the crank arm bolts (top and bottom) on the non-drive side using the 5mm Allen key. You may find that some models of the Shimano bottom bracket also have a small tab to pry up as well, a flat bladed screw driver works well for this.

Next step is to remove the end cap found on the end of the crank. The end cap is used for applying and setting the pressure on the crank arms.

Now remove the non-drive side crank arm you’ve loosened. Use a rubber mallet to tap out the drive side crank arm. Be gentle on the axel, so that you don’t damage it or the bottom bracket. Once the drive-side crank arm is loose and out, spin the inside of the bottom bracket using your hand/fingers. It should move easily and not feel loose or grindy. If only one side of the bottom bracket needs replacing, you might want to consider doing both (you have to buy both sides of the bottom bracket anyway). Keep the side of the bottom bracket that feels OK and throw out the bad side. You can replace just the bearings too but this is about the same price as replacing the whole bottom bracket and usually not worth it. I find that most bikes need their bottom bracket replaced once a year.

Now it’s time to remove the bottom bracket cups. They are left and right specific; the “right” side is reverse threaded. Remove both sides and take note of what spacers are on what sides? Clean the inside of the frame using a rag and make sure to get the dirt, sand, and water out too. Apply new grease to the frame and thread back in the new bottom bracket cups. Once the cups are back in, gently push the crank arms back through the bottom bracket. Make sure to start with the drive terrain side first. Once the crank and axle or in, push the other crank arm on to the axel, tighten down the adjustment cap, tighten up the 5mm bolts, push the plastic tab on, and place the chain back on the bike.

Please make sure the number of spacers on the bottom bracket is correct, that the cranks/pedals are pointing the opposite way too. It’s amazing how many times one will make this mistake.

That’s about it folks; time to go out for a ride and enjoy the trails.

Article by Dave Williams. Dave is a “wrench” for hire living in Banff, Alberta. He has provided bike support to riders participating in events including the TransRockies, 24 hours of Adrenaline, Sea to Summit, Full Moon and Raid the North. To get in touch with Dave, drop him a line at dave_williams[at]shaw.ca

Past articles by Dave: Prep your bike for spring, How to recentre your brakes, How to replace your chain: Part 1; How to replace your chain: Part 2