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.
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.
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.
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!