With spring on the way, and a winter of riding in wet and grimy conditions under the wheels, now may be a good time to inspect the bottom bracket.

Jon Hayes, mechanic at Dorset’s Ride cycle shop, demonstrates how to remove and inspect a Shimano HollowTech II bottom bracket.

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1)  Shift chain to inner ring

Shift down to the inner ring. This makes it easier to remove the chain from the chainring and rest it on the bottom bracket shell.

2) Remove left side crank arm

Using a 5mm Allen key, loosen the pinch bolts on left hand crank arm, and pull it from the one-piece bottom bracket axle. Remove safety clip from between crank arm bolts using a small screwdriver or pick. Remove end cap from left side crank arm with special tool (Shimano or Park). Pull left side crank arm from bottom bracket axle.

3) Remove right side crank arm

Grip the chainwheel ‘spider’ and pull the right side crank arm from the frame. This can also be achieved by tapping the left side of the bottom bracket axle with a rubber faced mallet.

4) Remove right side bottom bracket cup

Take a splined bottom bracket tool, attach to right side bottom bracket cup and rotate clockwise. The left side cup is loosened by turning in an anti-clockwise direction.

5) Clean bottom bracket threads

Take a rag and clean the bottom bracket threads, removing dirt, rust, swarf, or water build up.

6) Check bottom bracket cups

Turn the bearing within the cup to check its smooth rotation. If rough or ‘notchy’ replace the unit.

7) Apply grease and replace bottom bracket cups

Apply grease to threads of bottom bracket cup and shell. Using a grease gun will allow you to apply the grease accurately. Screw the bottom bracket cups back into the bottom bracket shell.

8) Refit right side crank arm

Push the right hand crank arm into the bottom bracket shell. Place the chain back on the inner chain ring to avoid unnecessary rubbing on the frame. Check the crank spins freely.

9) Refit left side crank arm

The left side crank arm will only fit at 180 degrees to the right side crank arm. Replace crank arm end cap using special tool.

10) Tighten crank arm pinch bolts

Using a 5mm Allen key, tighten the crank arm pinch bolts. Tighten the bolts one at a time, starting with the inside bolt. When the outside bolt has been tightened, tighten the inside bolt again. Refit the safety clip between the crank arm bolts.

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Many thanks to Jon Hayes and to Tim O’Rourke.

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