The Shimano SM-BB70 [paid link] Hollowtech II bottom bracket is a widely used component in road cycling, particularly favored for its reliability and smooth operation. However, even high-quality components like the SM-BB70 [paid link] can underperform or fail prematurely if installed incorrectly. This guide outlines the most common installation mistakes associated with the SM-BB70 [paid link], their consequences, and how to avoid them for a flawless set-up.
Incorrect Shell Preparation
One of the most overlooked yet critical steps is preparing the bottom bracket shell before installation.
The SM-BB70 is designed to thread into standard BSA (British) threaded shells. Failure to inspect and properly face the shell surfaces can cause misalignment between the cups. Even slight angular deviations can increase bearing wear and reduce drivetrain efficiency.
Ensure both sides of the shell are clean, free from paint overspray, and precisely faced. A proper facing tool guarantees smooth, aligned contact surfaces, which are essential for proper torque application and bearing longevity.
Cross-Threading During Installation
Cross-threading the SM-BB70 cups is a serious and often irreversible error. The aluminum threads of the cups and the frame’s shell can be damaged quickly if the threads are not aligned correctly from the outset.
Always begin threading the cups by hand to ensure proper engagement. The drive-side cup (typically marked with a directional arrow) uses a left-hand thread, while the non-drive side uses a standard right-hand thread. Misunderstanding this orientation often leads to forced installation and stripped threads.
Using a torque wrench [paid link] with a Shimano-compatible Hollowtech II bottom bracket tool [paid link] ensures the cups are secured evenly and accurately to Shimano’s specification of 35–50 Nm.
Neglecting to Use Appropriate Grease or Anti-Seize
Another frequent issue involves omitting proper lubrication during installation. Without a layer of grease or anti-seize compound, the threaded interfaces are vulnerable to galvanic corrosion, particularly between dissimilar metals like aluminum cups and a steel or titanium frame.
This not only makes future removal extremely difficult but can also compromise the structural integrity of the bottom bracket shell. Apply a uniform coating of waterproof grease or anti-seize compound on the threads before installation to avoid creaks, corrosion, and bonding over time.
Using Excessive Torque
While under-tightening can result in a loose fit, over-tightening is equally harmful. Applying torque beyond Shimano’s recommended specification can deform the cups or distort the bearing alignment, causing premature bearing failure.
Use a calibrated torque wrench [paid link] and follow Shimano’s specifications precisely. Over-torquing doesn’t improve stability—it accelerates component fatigue.
Installing Cups Without the Inner Sleeve (Spacer Tube)
The SM-BB70 includes a plastic inner sleeve that serves a critical function: protecting the crank spindle from water and debris ingress through the bottom bracket shell. Many users mistakenly discard this part, thinking it’s optional.
Omitting this sleeve increases the risk of internal corrosion, especially in wet or humid environments. Always install the sleeve between the two cups before tightening to ensure long-term reliability and internal cleanliness.
Incorrect Spacer Configuration
Spacer misplacement is another common error, especially on frames with non-standard shell widths or when installing on frames originally meant for different cranks.
The SM-BB70 is primarily designed for 68 mm or 73 mm threaded shells. Using the wrong number or positioning of spacers can lead to uneven bearing preload, side-loading the bearings and causing drag or creaking noises during pedaling.
Always consult Shimano’s documentation specific to your frame type and crank model. Improper configuration not only affects bearing life but also crankset alignment, leading to poor shifting and uneven wear.
Improper Bearing Preload Adjustment
Although the SM-BB70 doesn’t use external preload adjusters like some press-fit systems, the Hollowtech II crank design relies on accurate crank arm installation to apply the correct preload on the bearings.
Improper tightening of the left crank arm fixing bolt can either over-compress the bearings or leave them too loose. Always use the Shimano preload cap tool to lightly snug the cap before tightening the pinch bolts in the correct sequence and torque.
Failure to Recheck After Initial Rides
Even with a flawless initial installation, it’s critical to recheck torque settings after the first few rides. Settling of the grease, slight material deformation, or overlooked errors can manifest as creaks or unwanted movement.
Inspect the cups, crank arms, and fixing bolts for any signs of loosening and retorque them if needed. This ensures the system remains tight and noise-free under load.
Conclusion
Avoiding these common installation mistakes is essential for getting the best performance out of your Shimano SM-BB70 bottom bracket. Correct installation not only ensures smooth pedaling but also extends the life of both the bottom bracket and crankset. By adhering to best practices, understanding torque specs, and giving attention to frame preparation, riders can confidently rely on their SM-BB70 for many miles of efficient and trouble-free riding.