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How to: Replace your Bottom Bracket

Your bottom bracket is a part of your bike that is prone to wear. This guide will help you replace your bottom bracket.

Contents

In this how-to we look at four types of bottom brackets:
1. Square taper bottom bracket
2. External threaded bearing cups
3. Pressfit (BB86 and PF30)
4. BB30

If you don’t know which type of bottom bracket you have, we refer you to our blog ‘Bottom Brackets and Bottom Bracket Shells.’

1. Mounting a Square Tapered Bottom Bracket

To refresh your memory, this is a square tapered bracket:

Bottom Bracket
Shimano square bracket with Italian thread

Take in mind there are two different types:

  1. The BSA or English threaded bottom bracket. Recognisable because of the text BC1.37×25. This is also on the outside of the bottom bracket.
  2. Italian bottom bracket. Recognisable by the text 36×24. The bottom bracket has a right-handed thread. This means that both sides have to turn the same way in order to loosen it.

Tools

To mount a square tapered bottom bracket you need:

  • Shimano bottom bracket: bottom bracket remover
  • Campagnolo: cassette cap/bottom bracket removal tool
  • Assembly paste

1. Cleaning the thread and applying assembly paste

First clean the thread in the frame with a clean cloth. Then apply assembly paste generously on both sides. You can use your fingers or a brush. The paste makes it easier to re-attach the bottom bracket, and to remove it again later.

2. Now first attach the drive side

Leave the loose ring aside for the moment, and get the entire bottom bracket. This has to be fixed at the drive side. If you have a BSA threaded bracket, turn counter clockwise. Insert the Italian turning clockwise.

Then fix it as tight as you can with just your hands. If you feel resistance, then it is crooked, or there is still dirt in the thread. Never force it in, because you may damage the thread.

3. Secure it with the bottom bracket tool

Now attach the bottom bracket tool to the bracket. Because this can come off easily, you can hold it with the Trivio key.

If you don’t have one, you can also use a quick release to hold the key in place. Then screw it on tightly, but don’t overdo it. Fixed is fixed.

4. Fix non-drive side

Non-drive side
”Righty Tighty Lefty Loosey”

Now the drive side is fixed, you have to fix the loose cup on the other side. Repeat the steps, but keep in mind that the loose cup has to be fixed turning clockwise. This is the same for both the Italian and the BSA thread.

2. Fixing External Bearing Cups

bottom bracket montage externe lager cups
Shimano external bearing cups

External bearing cups are called external, because the bearings are partly outside the frame. It has a wider diameter, so it is possible to use a hollow axle that is also wider, which means that the unit is stiffer as a whole.

Necessary Tools

  • Bracket key for external bottom bracket cups
  • Assembly paste

1. Cleaning the thread and applying the assembly paste

First clean the thread in the frame with a clean cloth. Then apply the mounting paste generously on both sides. You can use your fingers or a brush. It makes it easier to screw in the axle, and also loosen it again later.

2. Spacer ring (only for mountain bike)

Spacers voor de MTB bottombracket
Spacers for the MTB bottom bracket

Mountain bikes often have spacer rings. In the chart below you can see which spacer you have to use. It is the same for SRAM, RaceFace and FSA cranksets.

3. First screw in the drive side

Leave the ring for what it is now, and get the entire bottom bracket first. This has to be attached at the drive side. A BSA is fixed counter clockwise, an Italian thread turns clockwise in order to fixate it.

First screw it in using your hands. If you feel resistance from the start, it is probably crooked or there is dirt in the thread. Never force it in, because you’ll damage the thread.

4. Fix it with a bottom bracket tool

externe cups indraaien
Drive-side Italian thread: clockwise is tight

Now use the bottom bracket tool on the external cup. It can come off easily, so take care. Fix it tightly, but don’t overdo it. Fixed is fixed.

5. Attach non-drive side

Now the drive side is in, you still have to attach the external bearing on the other side. Repeat the steps, but keep in mind to turn the cap clockwise (same for Italian and BSA thread).

3. Mounting Press Fit Bearings (BB86 and PF30)

bottom bracket montage pressfit BB86 en PF30
GXP Pressfit bearings for MTB

Press fit is a bearing system that has been applied more and more recently. We will help you mount a press fit bottom bearing in this guide.

Necessary Tools

  • Press fit press tool
  • Assembly paste

1. Cleaning bottom bracket tube and applying assembly paste

First properly clean the bottom bracket of your frame. Then apply mounting paste generously on both sides. You can use your fingers or a brush. The paste will make it easier to fix the bottom bracket and prevents a creaking bracket in the future

2. Spacer rings, only mountain bikes

First look at the manual or on the manufacturer’s website to see if the rings have to be placed left or right.

3. Mounting bearings

Pressfit tool
With a pressfit tool there are no excuses to not service your bike regularly.

Attach the bearing to the press fit press tool, then put it through the bottom bracket. Then attach the other side, and finally add the ring of the press. It should look like this:

4. Fixing the bearings

Fix the bearings to the frame. First take care that the bearings are straight on the bottom bracket so you’ll press them in correctly. Then turn the press until it won’t go in further. Then remove it.

4. Installing BB30 Bottom Bracket Bearings

If you have a BB30 ready frame, the bottom bracket bearings are loose in the frame. Don’t mix up with a Press Fit BB30. BB30 bearing looks like this:

BB30 trapas
BB30

Tools

To assemble your BB30 bottom bracket you need:

  • BB30 press tool
  • Assembly paste

1. Attaching the circlip

Circlip BB30
Don’t forget the circlip!

The bearings are kept in place by so-called circlips. Inside the bottom bracket shell are two slits, in each of which should be a clip. These make sure the bearings can’t be pressed in. The ends of the clip can be pulled together with a pair of pliers.

If the ring doesn’t have holes, then you can use your hands. First put in one side then press in the other side. Then apply assembly paste.

2. Attaching BB30 bearings

First attach the bearing to the press, then put the tool through the bottom bracket. Then attach the other side, and finally the ring of the bottom bracket press. It should look like this:

BB30 pers
BB30 press

3. Fixing it

Now fix the bearings to the frame. But take care the bearings are straight on the bottom bracket, then you can press them in smoothly. Now tighten it with the press, until you can’t go further. The bearings are attached correctly now. Before you attach your crankset, apply some assembly paste again. This prevents wear.

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Kees Neijenhuis

Kees Neijenhuis

Enthusiastic trail runner and mountain biker. I love being outdoors! I also have a weak spot for beautiful products and true craftsmanship. Rides a Trek Top Fuel 9.7 SL 2018.

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