The Shimano SM-BB93 [paid link] bottom bracket is a popular choice for high-performance road bikes using Hollowtech II cranksets. As a press-fit style component designed for Shimano’s 68 mm and 73 mm threaded bottom bracket shells, it offers exceptional weight savings and efficient power transfer. However, improper installation and maintenance of the SM-BB93 [paid link] can lead to noise, creaking, poor crank alignment, and even frame damage over time. This guide identifies critical errors to avoid when handling this bottom bracket, helping you get the most out of your drivetrain setup.
Incorrect Shell Preparation Before Installation
Proper shell preparation is essential when installing the SM-BB93 [paid link]. Failing to clean, face, and chase the bottom bracket shell can result in poor bearing alignment. This misalignment increases resistance and wear on the bearings, potentially causing premature failure.
Many users skip re-facing the shell, assuming new frames are ready-to-install. However, even minor irregularities can cause misalignment. Always ensure the bottom bracket shell is free of debris, corrosion, and excess paint. Use a facing tool to achieve smooth, parallel surfaces on both sides of the shell.
Using Excess Grease or Incorrect Lubricants
Shimano specifies moderate grease application for the threads and contact surfaces. Over-greasing the shell or the cups can trap dirt, interfere with proper torque application, and attract moisture. Conversely, under-greasing may promote creaking and seizing between components.
Another common error is using anti-seize compound instead of grease. While anti-seize has its place on metal-to-metal interfaces, it is not suitable for plastic or composite cups like those found in the SM-BB93, as it can degrade the material over time.
Cross-Threading the Bottom Bracket Cups
Despite being a threaded component, many mechanics rush the threading process, particularly when using power tools. Cross-threading the cups not only ruins the threads of the SM-BB93 but also damages the frame’s bottom bracket shell. This can be an expensive and irreversible mistake.
To avoid this, always start threading by hand. Apply light pressure and ensure the cup is square to the shell before using any torque wrench [paid link] or bottom bracket tool [paid link]. Shimano recommends tightening to 35–50 Nm, which should be confirmed using a torque wrench [paid link].
Incorrect Cup Orientation During Installation
The SM-BB93 features a left-hand thread on the drive side and a right-hand thread on the non-drive side. Confusing these threads during installation can strip the bottom bracket shell, especially if excessive force is used.
This mistake is particularly common among first-time mechanics. Always check orientation markings stamped on the cups. Remember: the drive-side cup tightens counterclockwise; the non-drive-side tightens clockwise.
Neglecting Periodic Inspection and Maintenance
Unlike press-fit systems, the SM-BB93 offers improved sealing. However, this doesn’t eliminate the need for regular inspection. Water, sweat, and road grime can still infiltrate the system over time.
Neglecting routine checks can allow contaminants to sit within the cups, leading to rust, increased bearing drag, or creaking noises. It is advised to remove and inspect the bottom bracket at least every 5,000 km or during annual maintenance intervals.
Improper Torque Application
Many installation errors trace back to improper torque. Under-torquing leads to loose cups and creaking, while over-torquing can deform the cups or strip threads.
The Shimano SM-BB93 requires torque settings between 35 and 50 Nm. Always use a properly calibrated torque wrench [paid link]. Torque each side gradually, alternating between sides to ensure even pressure distribution across the bottom bracket shell.
Not Checking for Shell Type Compatibility
Some mechanics assume the SM-BB93 is universally compatible with all threaded bottom bracket shells. However, this model is designed specifically for 68 mm and 73 mm BSA (British Standard Thread) shells.
Using it with Italian-threaded frames or PF30 [paid link]-type press-fit shells is a common and damaging mistake. Doing so compromises the bottom bracket’s integrity and causes alignment issues. Always confirm frame compatibility before selecting a bottom bracket.
Reusing Damaged or Worn Bottom Bracket Cups
Reusing cups from a previously installed SM-BB93 bottom bracket is a false economy. The plastic cups are prone to deformation over time, especially if they were removed using improper tools or force.
Damaged cups can no longer provide precise bearing alignment and may allow water ingress. Always replace the full unit rather than attempting to reuse old parts. Shimano bottom brackets are cost-effective enough to warrant replacement rather than risking drivetrain integrity.
Improper Tool Usage for Installation or Removal
Using incorrect tools—such as adjustable wrenches, strap wrenches, or makeshift adapters—can damage the SM-BB93’s plastic cups. Shimano provides specific tools like the TL-FC32 [paid link] or TL-FC36 [paid link] for installing and removing bottom brackets safely.
Investing in the right tool not only protects the bottom bracket but ensures you apply consistent torque. Improvised methods can crack the cups or score the frame’s shell, leading to more complex repairs.
Failing to Account for Crankarm Preload
After installing the SM-BB93, the Hollowtech II crankset must be preloaded correctly using Shimano’s plastic preload cap. Many riders overlook this step or over-tighten the preload cap, resulting in side-loading the bearings and rapid wear.
The crank preload cap should be snug, not torqued. Once the cap is set, secure the pinch bolts on the non-drive side arm to retain position. Skipping this step creates play in the crank or places excessive pressure on the bearing faces.
Conclusion
Avoiding these common SM-BB93 bottom bracket mistakes can dramatically improve drivetrain performance and longevity. Precision during installation and regular maintenance checks ensure you get the full benefit of Shimano’s lightweight and efficient bottom bracket design. Always follow manufacturer specifications and invest in the correct tools to avoid irreversible damage.