Shimano XT BSA BB-MT801 MTB bottom bracket – IBBMT801B

The Shimano XT BB-MT801 is a bottom bracket designed for Shimano MTB drivetrains fitted with a Hollowtech II bottom bracket axle. This BSA version fits frames with a threaded bottom bracket shell and offers a reliable solution to ensure smooth crankset rotation.

Listed under part number IBBMT801B, this Shimano XT bottom bracket features sealed bearings and a design engineered to withstand the stresses encountered in mountain biking. It is an ideal replacement part for the maintenance or refurbishment of a compatible Shimano drivetrain.

The BB-MT801 is specifically designed for Shimano cranksets fitted with a 24 mm axle, in accordance with the configuration specified by Shimano.

Key features of the Shimano XT BB-MT801

• Shimano XT bottom bracket designed for mountain biking.
• BSA threaded standard for compatible frames.
• Compatible with Shimano Hollowtech II cranksets with a 24 mm axle.
• Sealed bearings to minimise the ingress of contaminants.
• Designed to withstand the rigours of off-road riding.
• The ideal solution for replacing a worn or loose bottom bracket.
• Restores smoother crankset rotation.
• Shimano part number: BB-MT801 / IBBMT801B.
• Available in versions to suit different frame bottom bracket widths.

What is a BSA bottom bracket?

The BSA standard refers to a threaded cup bottom bracket that is screwed directly into the frame. It is widely used on mountain bikes and allows for relatively simple installation and removal with the appropriate tools.

Before ordering a BB-MT801, however, it is important to check that your frame does indeed have a threaded BSA bottom bracket and that its width corresponds to the version of the bottom bracket you have chosen.

In particular, the BB-MT801 must not be confused with a bottom bracket designed for a Press-Fit frame.

Hollowtech II: a design tailored to cranksets Shimano

Shimano ’s Hollowtech II uses bearings positioned outside the frame. This design ensures good stiffness of the entire crankset whilst maintaining smooth operation.

The BB-MT801 is designed for Shimano cranksets using a 24 mm axle compatible with this technology.

When replacing the bottom bracket, it is recommended that you also check the condition of the bottom bracket spindle, spacers and seals. A new bearing will not be able to compensate for a problem arising from another component in the assembly.

When should you replace your bottom bracket?

There are several signs that a bottom bracket is reaching the end of its service life:

• play developing in the crankset;
• creaking or noises whilst pedalling;
• uneven or rough rotation;
• a feeling of resistance in the bearings;
• corrosion or contamination;
• damaged bearings following intensive use or in damp conditions.

On a mountain bike regularly used in mud, water or dust, regular checks of the bottom bracket are particularly important.

Expert tip: if your old bottom bracket has play or bearings that ‘scrape’, it is better to replace both cups than to try to salvage a worn bearing. You should also take advantage of the disassembly to thoroughly clean the bottom bracket area and check the condition of the BSA thread.

Fitting the BB-MT801

Replacing a Hollowtech II bottom bracket requires tools suitable for the cups Shimano.

The general procedure is as follows:

1. Removing the crankset.
2. Removing the old bottom bracket cups.
3. Carefully clean the frame threads.
4. Check the bottom bracket width and the required spacers.
5. Grease or prepare the threads in accordance with the recommendations Shimano.
6. Screw the BB-MT801 cups in the correct direction.
7. Tighten the cups to the torque specified by the manufacturer.
8. Fit the crankset and carry out the necessary adjustments.
9. Check for play and ensure smooth rotation.

The direction in which the bottom brackets are screwed in differs between the drive side and the non-drive side. If in doubt, it is best to refer to the documentation at Shimano or have the work carried out by a bicycle workshop.

Technical specifications