Shimano XT BB-MT800 BSA Threaded Bottom Bracket Instruction Manual

1. Product Overview

The Shimano XT BB-MT800 is a BSA threaded bottom bracket designed for bicycle cranksets utilizing the Hollowtech II system. It features durable aluminum cups and steel bearings, engineered to provide smooth and reliable pedaling performance across various riding conditions. This component is crucial for connecting the crankset to the bicycle frame, ensuring efficient power transfer.

Image: Shimano XT BB-MT800 Bottom Bracket. This image displays the complete bottom bracket unit, showing the threaded cups and the central spindle sleeve.

2. Setup and Installation

Proper installation is essential for the longevity and performance of your bottom bracket. Ensure your bicycle's bottom bracket shell is clean and free of debris before beginning. The BB-MT800 is designed for 68mm or 73mm shell widths and uses English threading.

2.1 Identifying Left and Right Cups

The bottom bracket cups are marked 'L' for left and 'R' for right. The right cup (drive side) typically has a reverse thread (tightens counter-clockwise), while the left cup (non-drive side) has a standard thread (tightens clockwise). Always confirm the threading direction before installation to prevent damage.

2.2 Preparation

• Clean the bottom bracket shell threads thoroughly.
• Apply a thin layer of grease to the threads of both the bottom bracket shell and the bottom bracket cups. This aids in smooth installation and helps prevent corrosion and creaking.

2.3 Installation Steps

1. Begin by hand-threading the right (drive side) cup into the bottom bracket shell. It should turn smoothly without resistance. If resistance is met, re-check the threading and ensure it's not cross-threaded.
2. Once hand-tight, use a compatible bottom bracket tool to fully tighten the right cup to the manufacturer's specified torque.
3. Repeat the process for the left (non-drive side) cup, ensuring it is also hand-threaded smoothly before using the tool to tighten to the specified torque.
4. The bottom bracket includes three 2.5mm spacers. Consult your crankset's instructions for proper spacer placement, as this varies depending on the crankset model and frame shell width.
5. Install your Hollowtech II compatible crankset according to its specific instructions.

3. Operation

The Shimano XT BB-MT800 bottom bracket provides a stable and low-friction interface for your bicycle's crankset. Its sealed cartridge unit design protects the internal steel bearings from dirt and moisture, ensuring consistent and smooth rotation during pedaling. The external bearing design contributes to increased stiffness and durability, enhancing overall pedaling efficiency.

4. Maintenance

To ensure optimal performance and extend the lifespan of your Shimano XT BB-MT800 bottom bracket, regular maintenance is recommended:

• Cleaning: Periodically clean the exterior of the bottom bracket and the surrounding frame area to remove accumulated dirt and grime.
• Inspection: Regularly check for any signs of play or looseness in the crankset or bottom bracket. If any play is detected, re-torque the bottom bracket cups and crankset bolts according to manufacturer specifications.
• Grease: The bottom bracket comes pre-greased with a specific amount of lubricant. Do not attempt to remove excess grease from the seals, as this grease is intentionally placed to protect the bearings and facilitate crank installation.
• Replacement: While designed for durability, bottom brackets are wear items. If you notice persistent creaking, grinding, or excessive play that cannot be resolved with cleaning or re-torquing, it may be time for replacement.

5. Troubleshooting

Common issues and their potential solutions:

• Creaking Noise:
  • Ensure bottom bracket cups are tightened to the correct torque specifications.
  • Verify that the crankset is properly installed and torqued.
  • Check for sufficient grease on the threads and contact points during installation.
  • Inspect the bottom bracket shell for any damage or irregularities.
• Rough or Grinding Feel:
  • This often indicates worn bearings. If cleaning and re-greasing the crank spindle does not resolve the issue, the bottom bracket may need replacement.
• Play in Crankset:
  • Confirm that the crankset is fully seated and all bolts are tightened to specification.
  • Check if the bottom bracket cups are securely tightened.
  • Excessive play after verifying proper installation may indicate worn bearings or an incorrect bottom bracket/crankset combination.

6. Specifications

7. Recommended Tools

For proper installation and removal of the Shimano XT BB-MT800 bottom bracket, a compatible bottom bracket tool is required. The Park Tool BBT-69.4 is an example of a suitable tool for 16-notch, 44-45mm outer diameter bottom bracket cups.

8. Warranty and Support

This Shimano product comes with a Limited Warranty. For detailed warranty information, claims, or technical support, please refer to the official Shimano website or contact your authorized Shimano dealer.

You can visit the official SHIMANO Store for more product information and support resources.