Technical FAQ: Bottom bracket bearing wear

Why are my bottom bracket bearings wearing out so quickly?

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Dear Lennard,
I currently have an FSA k-force light compact crankset on my ‘cross bike (and my road bike too). I like the cranks, it’s the bottom bracket I am not too happy with. The non-drive side bearings went out on me after seven races (they were even uncharacteristically dry races).

Interestingly I know of at least three other riders with similar stories about the non-drive side of the MegaExo bottom bracket. I was able to clean most of the gunk out and repack them; but the only recovered so far. I just acquired a set of Enduro bearings, which have slightly larger balls to replace them with and I hope that will cure my ills.

If that does not work, I would really love to move to Chris King’s bottom bracket. If that part is half as good as their headsets I would be overjoyed. However when I asked King if their bottom bracket was compatible with FSA cranks, the reply was that the King bottom bracket is built to Shimano’s HollowTech II standard. If FSA cranks are built to that standard, then the bottom bracket will work. Given that FSA cranks are moderately popular, I was hoping for something a bit more definitive.

Can you tell me whether or not the FSA k-force light crank will work with a King bottom bracket?

Dear LeRoi,
Definitely the bearing diameter of both the Enduros and the Chris King will work, because you can run a Shimano Hollowtech II crank in an FSA MegaExo bottom bracket and vice versa. The spindle diameter in both cases is 24mm, and both use a 7mm thick bearing. However, your FSA K-Force Light crank has slightly less width from arm to arm. I know because the kit does not yet exist to fit one on a Trek Madone.

The Enduro bearings will not work, either, because those are 7mm bearings, not 6mm ones.

FSA’s K-Force Light (and its other carbon cranks) use a slightly narrower bottom bracket than FSA alloy cranks (which are similar to the Shimano Hollowtech II size) and incorporate a wave spring washer to allow better bearing preload.

See more on this below from Dae Oh of FSA’s tech department.

Checking the width.

Checking the width.


Answer from FSA’s Dae Oh

The short answer; no, the FSA K-Force Light Rd. Crank is not compatible with a Chris King bottom bracket (made to Shimano compatible dimensions). Also, the K-Force Rd. crankset will not be compatible either.

The FSA BB8200 (meant for K-Force Light) uses a 6 mm width bearing. This allows us to make the bottom bracket outside to outside dimension more narrow providing room for a wave washer. The BB8000 (meant for K-Force) does indeed use a 7 mm width bearing, yet its design does not allow for use of a Chris King bottom bracket.

However our popular alloy cranksets, the Gossamer Rd. and the Energy Rd. is compatible with the Chris King bottom bracket (made to Shimano compatible dimensions). These cranks use BB6000, this BB’s dimensions are compatible with Shimano.
Dae Oh
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