Why Your SM-BB93 Might Not Be Set Up Correctly and How to Fix It

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The Shimano SM-BB93 [paid link] is a Hollowtech II bottom bracket specifically designed for road bikes using 68mm threaded bottom bracket shells. As a high-performance component for Shimano’s Dura-Ace series, precision installation is critical to ensure long-term performance and drivetrain efficiency. However, many riders encounter issues due to improper setup. This guide identifies the most common installation and performance issues related to the SM-BB93 [paid link] and provides practical, technical solutions for achieving a flawless configuration.

Understanding the SM-BB93 Bottom Bracket

The SM-BB93 [paid link] is a threaded, external cup bottom bracket engineered for Shimano Hollowtech II road cranks. It is known for its lightweight construction, reduced friction, and improved sealing over its predecessors. Proper installation of the SM-BB93 ensures crankset alignment, minimizes bearing drag, and prolongs component lifespan.

Common Signs of Incorrect SM-BB93 Setup

Improper installation of the SM-BB93 can manifest through various symptoms:

  • Creaking or clicking noises during pedaling
  • Unusual bearing drag or rough rotation of the crankset
  • Lateral crank arm play, even after tightening the preload cap
  • Misaligned chainline, leading to poor front shifting performance
  • Premature bearing wear and water ingress

These symptoms often indicate either poor installation practices, incorrect tool use, or incompatibility with the frame or crankset.

Thread Preparation Errors

One of the primary causes of setup issues is poor thread preparation on the bottom bracket shell. Before installing the SM-BB93:

  • Ensure the bottom bracket threads are clean and free of paint, debris, or corrosion. Contamination can prevent proper torque application or cause cross-threading.
  • Chase and face the bottom bracket shell. If the faces are not parallel, bearing misalignment can occur, resulting in premature wear and drag.

Neglecting thread preparation often results in uneven cup threading, leading to misalignment and internal stress on the bearing races.

Incorrect Cup Orientation and Torque

The SM-BB93 features left and right bearing cups that must be installed in the correct orientation:

  • The right-side cup (usually marked with an “R”) must be threaded into the drive side of the shell and is reverse-threaded (tightens counter-clockwise).
  • The left-side cup goes into the non-drive side and uses a standard thread (tightens clockwise).

Incorrect orientation or over-torquing can lead to thread damage or bearing compression. Shimano recommends torquing the cups to 35–50 Nm, using a Shimano-compatible Hollowtech II bottom bracket tool [paid link] to ensure even pressure and alignment.

Overlooked Spacer Configuration

Although the SM-BB93 is generally used in 68mm English-threaded shells that do not require spacers, using incorrect or extra spacers during installation can significantly alter chainline and bearing load:

  • Do not install spacers unless specified by frame or crankset manufacturer.
  • Using spacers with a 68mm shell and a road crankset will result in crank misalignment and improper preload tension.

Always refer to Shimano’s technical manual and your frame’s compatibility chart before adding spacers.

Preload Cap Misuse

The SM-BB93 system uses a plastic preload cap to set axial tension on the bearings. A common setup error is over-tightening the preload cap, which can:

  • Cause excess pressure on the bearings, reducing smoothness and causing premature failure.
  • Lead to lateral crank arm play once the crank bolts are torqued, as preload was incorrectly set.

Tighten the preload cap just enough to eliminate crank play and then torque the pinch bolts to spec (12–14 Nm). Always tighten the pinch bolts alternately in small increments to evenly distribute load across the spindle.

Frame Tolerance Mismatch

Although SM-BB93 is designed for standard BSA threaded shells, poorly machined frames can lead to thread engagement issues or poor alignment:

  • If the threads don’t allow full cup insertion, bearing load becomes uneven, which creates drag and leads to creaking.
  • When in doubt, have the shell inspected and re-faced by a professional mechanic to restore proper cup seating.

Frame quality directly influences the bottom bracket’s performance. Tolerances out of spec will continue to cause issues regardless of how well the SM-BB93 is installed.

Environmental Factors and Seal Failure

Despite the SM-BB93 having improved seals compared to earlier models, water intrusion is still a known issue if setup is improper:

  • Improperly torqued cups allow water to seep into the threads.
  • No anti-seize compound or waterproof grease on threads can promote corrosion and creaking.

To prevent these problems, apply a thin layer of grease or anti-seize compound on both cups and frame threads. Regular inspection for moisture is recommended if riding in wet climates.

Bearing Press Fit and Drag

If the crank spindle is not clean or if there’s foreign material inside the bearing races, the spindle may not seat fully or may bind, creating drag. Ensure:

  • Spindle is spotless and lightly greased before insertion.
  • Bearings rotate freely before installing crank arms.

Failure to perform this step often results in immediate resistance during crank rotation, often misdiagnosed as a bearing fault.

Conclusion

A poorly installed Shimano SM-BB93 bottom bracket can significantly compromise your bike’s performance. From thread preparation and torque accuracy to spacer misuse and preload errors, even minor oversights can result in frustrating creaks, drag, or component failure. By following Shimano’s guidelines precisely, preparing your frame properly, and using the correct tools and torque values, you can ensure a smooth and long-lasting setup.

FAQs About SM-BB93 Set-Up Errors

1. What torque should I use for the SM-BB93 bottom bracket cups?
Use 35–50 Nm of torque with a compatible Hollowtech II tool.

2. Should I use spacers with SM-BB93 on a 68mm shell?
No. The SM-BB93 is designed to be used without spacers on 68mm shells unless specified otherwise by Shimano.

3. Why does my SM-BB93 setup creak during pedaling?
Creaking is usually caused by improper torque, contaminated threads, or frame tolerance issues.

4. Can I install the SM-BB93 without facing the bottom bracket shell?
You can, but it’s not recommended. Facing ensures both cups sit evenly, which prevents bearing misalignment.

5. What grease should I use on the threads?
Use waterproof bike-specific grease or anti-seize compound to prevent corrosion and creaking.

6. How do I know if the preload cap is too tight?
If the crank arms feel resistant to spin freely or bearings feel rough, the preload is likely too tight.