Avoid These Costly SM-BB70 Mistakes That Can Wreck Your Set-Up

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The Shimano SM-BB70 [paid link] Hollowtech II bottom bracket is a dependable component designed for road cyclists who expect durability and efficiency. While it’s engineered for performance, improper handling during installation or maintenance can cause early wear, noise, and even drivetrain damage. This guide walks through the most common SM-BB70 [paid link] mistakes that can ruin your set-up, with technical insights on how to prevent them.

Improper Frame Preparation

Before installing the SM-BB70, the bottom bracket shell must be properly faced and chased. Many riders skip this essential preparation, especially on carbon or aluminum frames.

When the shell isn’t properly faced:

  • The bearing cups won’t seat squarely, leading to misalignment.
  • Bearing load increases, which causes premature wear or binding.
  • You may experience creaking due to uneven torque distribution.

Shell preparation should always be performed using a facing and chasing tool set to ensure perfect parallelism and thread integrity. If you’re unsure about your frame’s state, consult a professional mechanic before threading in the SM-BB70 cups.

Using the Wrong Tools

The SM-BB70 requires Shimano’s Hollowtech II-compatible bottom bracket tool [paid link] (like TL-FC32 [paid link] or TL-FC36 [paid link]) for correct torque and engagement. Using adjustable wrenches or generic spline tools can damage the cup splines or lead to uneven installation torque.

Improper tools also risk:

  • Rounding off the cup notches.
  • Uneven preload on the bearing races.
  • Over-torquing, which could crush the shell threads or deform the frame.

Always use the correct Shimano-specific tool and a torque wrench [paid link] to ensure the cups are installed to the recommended 35–50 Nm.

Incorrect Spacer Configuration

This is a surprisingly common mistake, especially on English-threaded bottom brackets like the SM-BB70. Depending on the chainline, bottom bracket shell width (68mm or 73mm), and crankset type, the configuration of the included plastic spacers changes.

Errors in spacer installation lead to:

  • Crank arms sitting too far out or too close, affecting chainline.
  • Poor front derailleur alignment and shifting quality.
  • Over-compression of bearings if extra spacers are incorrectly added.

Consult Shimano’s installation chart carefully. For example, a 68mm shell typically requires two 2.5mm spacers—one on each side. Adding or omitting a spacer can drastically affect crank performance and bearing life.

Over-Lubricating or Under-Lubricating Threads

The SM-BB70’s threads must be installed with anti-seize compound or grease, but many either use too much or skip lubrication altogether.

Too much grease may:

  • Attract dirt and grit over time.
  • Increase the likelihood of cups loosening from the frame.

Too little or no grease:

  • Promotes galvanic corrosion in metal frames.
  • Causes creaking or seizing of cups inside the shell.

A thin, even coating of waterproof grease is ideal for steel and aluminum frames, while anti-seize is better suited for titanium or mixed-material builds.

Neglecting to Preload the Crank Correctly

Although the SM-BB70 itself does not include crank preload functionality, it is part of the larger Hollowtech II system. Once installed, the left crank arm’s preload cap must be adjusted to eliminate side play without adding load to the bearings.

Improper preload causes:

  • Bearing side-load that shortens lifespan.
  • Lateral crank movement that causes creaking or misalignment.
  • Poor power transfer efficiency under load.

Use the plastic crank cap tool to snug the cap just enough to eliminate play—tightening it by hand without tools is usually sufficient. Then secure the pinch bolts to Shimano’s torque spec (12–14 Nm).

Skipping Regular Bearing Checks

Many treat the SM-BB70 as a “fit and forget” bottom bracket, but it requires regular inspection—especially for riders who train in wet or dusty conditions.

Common neglect signs include:

  • Gritty or rough bearing feel.
  • Water ingress leading to corrosion.
  • Seized or stuck crankarms due to worn bearings.

Shimano recommends checking bearing condition every 2,000–3,000 km. Spin the cranks by hand and feel for roughness or resistance. Replace the bottom bracket if you detect play, contamination, or binding.

Installing in a Contaminated Shell

Dirt or metal shavings inside the shell during installation are a recipe for noise, misalignment, and wear. Always clean the bottom bracket shell thoroughly before threading in the cups.

Common contaminants include:

  • Carbon dust from frame prep.
  • Old thread locker residue.
  • Grease mixed with road grime.

Use isopropyl alcohol or a frame-safe degreaser to ensure a clean, dry shell before greasing and threading the cups. Any foreign material inside the shell increases torque inconsistencies and misalignment.

Misdiagnosing Creaks from Other Components

A noisy drivetrain doesn’t always mean your SM-BB70 is at fault. Creaks commonly blamed on bottom brackets can originate from:

  • Crank arm interfaces.
  • Pedals.
  • Chainring bolts.
  • Frame contact points.

Before removing the SM-BB70, isolate the noise source with methodical troubleshooting. Removing and reinstalling the bottom bracket prematurely increases wear and thread fatigue unnecessarily.

Overlooking Compatibility with Hollowtech II Cranks

Although the SM-BB70 is designed for Hollowtech II systems, not all cranks fit identically. Cranks from different series (e.g., Deore, Ultegra, or 105) may have subtle interface differences that affect chainline or bearing load.

Check Shimano’s compatibility charts to confirm:

  • Spindle diameter and length.
  • Chainline match for your front derailleur.
  • Preload system compatibility.

Installing an incompatible crank can cause noise, bearing overload, or poor shifting. Always pair the SM-BB70 with its intended crank family for optimal performance.

Conclusion

The Shimano SM-BB70 is a high-quality bottom bracket that can deliver years of reliable performance—but only if it’s installed and maintained with precision. By avoiding the common mistakes outlined above, you’ll ensure smooth operation, minimize noise, and extend your component lifespan.

Frequently Asked Questions (FAQs)

1. How often should I replace the SM-BB70 bottom bracket?
Shimano recommends inspecting the SM-BB70 every 2,000–3,000 km and replacing it when bearings feel rough, gritty, or exhibit play. In ideal conditions, it may last up to 10,000 km.

2. Can I use the SM-BB70 with a non-Shimano crankset?
It’s designed for Hollowtech II cranksets. Some third-party cranks are compatible, but always verify spindle length, diameter, and chainline specifications.

3. What grease should I use on the threads during installation?
A waterproof assembly grease works well for steel and aluminum frames. Use anti-seize compound for titanium frames to prevent galvanic corrosion.

4. My crankset is wobbling—could the bottom bracket be the issue?
Yes, but first check for proper crank preload, bearing wear, and correct spacer installation. Wobble often results from improper torque or bearing side play.

5. Is the SM-BB70 suitable for gravel or cyclocross bikes?
While designed for road use, it can handle off-road conditions if sealed properly. Expect more frequent maintenance due to mud and water exposure.

6. How can I check if the bearing cups are properly aligned?
Cup misalignment can be detected if the cranks feel resistant when turning or make noise under load. Frame facing and accurate cup torquing prevent this issue.