I’d recently switched to my Commencal Normal Disc ’08 winter commuter bike, and during preparation I’d noticed some corrosion on the bottom bracket. Then, even more recently, I broke a pedal off it on my morning commute, stripping the threads out of the crank and rendering it unrideable.
There’s only one thing for it: it’s time to get oily and remove the crankset and bottom bracket.
The Commencal still had its stock crankset, a square taper Truvativ Isoflow with 175mm cranks and MTB standard 42-32-22 rings. I decided against changing it for a “trekking” model with larger rings because of the hassle and expense of moving or possibly changing the front derailleur that would be involved, though such a unit might have been better for the type of use the bike sees.
Removing the crankset requires a crank puller tool and an 8mm hex key (Allen Key) or driver bit. I found a hex bit fitted to a ratchet spanner was the best tool for the job, giving more than adequate leverage to remove the crank retaining bolts and push the cranks themselves off the axle. I didn’t try, but I think I might have broken my 8mm hex key if I’d used it instead.
Removing the crankset
With the crankset now removed, I tested the rotation action of the bottom bracket axle by hand and could feel the bearings grinding. No doubt then, I needed a new one. The bottom bracket was visibly corroded and seized in place, so uncareful application of WD40, Large Spanner (fitted to a bottom bracket removal tool) and Heavy Hammer was required to release it.
 The bottom bracket was corroded and seized in place... |
 ...so the Large Spanner was applied, uncarefully |
Once free, the bracket was revealed to be an unsealed unit with its bearing races caked in sandy grime. Those poor bearings, they never stood a chance! Fortunately though, once cleaned, the aluminium frame of the Commencal inside the bottom bracket mounting looked to be in good condition.
 The bottom bracket was in a bad way... |
 ...but fortunately the frame itself was undamaged |
Now I have the cranks and bottom bracket removed, I can accquire replacements of the correct size and specification. No doubt I’ll post again after I’ve fitted them!
John, must get you some grease for that new BB – ouch!