Get to the bottom of it!

Learn how to fix that loose bottom bracket

Bottom brackets are one of those industry pet peeves that have plenty of ‘standards’ but no definitive standard. It’s one of the areas of the bike that people seem most hesitant about working on. That’s understandable, it’s the part of the bike you’re more or less standing on, but with the right tools and some help, it’s pretty straightforward.

Here, we show you how to solve a loose Shimano Hollowtech 2 bottom bracket, which can be caused by hasty factory installation or slight under-torquing on replacement. To tell a loose BB apart from a worn one with bearing play, take hold of each crank arm and waggle them from side to side. If a gentle movement offers an easy but slight movement, it’s bearing play and the BB is wearing out. A heftier haul sideways resulting in a single ‘clunk’ shows the BB cups moving in the frame. Either way, you’ll need to have a BB out and put one back in.

01 A LIT TLE LIF T

Use a 5mm Allen key to loosen the opposing pinch bolts on the lefthand crank arm. A small screwdriver will help lift the plate in the gap with the retaining pin, it will pivot out of the way on the inside pinch bolt. Use the correct tool (see box out) to remove the plastic preload bolt.

02 A xle out

Encourage the crank arm off, then use a rubber mallet to help the axle and driveside arm out of the bottom bracket. Don’t go full Hulk on this. As the axle slides out, drop the chain off the rings so it’s not flexed in the wrong direction.

03 In order

Lay parts out in the order they come off and use the bottom bracket spanner to loosen the cups. The driveside is an opposite thread. Both sides undo towards the front of the bike at the top of rotation. One will come out with the sleeve.

04 Clean components

Clean and inspect all components, plus the bottom bracket shell. Ensure no threads are damaged and pay attention to end faces on the end of the shell. If they are painted or unevenly worn, get them faced. Clean everything thoroughly.

05 Grease is the word

Grease and reinstall the BB. Shimano’s recommended torque is 35-50Nm. If you don’t own a torque wrench with such a range, that equates to pretty darned tight. Grease the axle and reinstall the driveside crank arm and axle.

06 Push the plate

Fit the non-drive arm, ensure it’s the correct position and slide onto the axle. Push the plate with the retaining pin into place, preload the setup with the plastic bolt. Alternate tightening of the two pinch bolts and torque to 14Nm.