BB: open or sealed?

BB: open or sealed?

I have an audax bike that Cobra Cycles (Preston) built for me in 1994. It was a custom job done in 531C and has seen better days. I have asked Graeme Scott from Happy Trails to renovate this old bike for me.

Graeme is unsure about the bottom bracket. It’s an open design. I think it’s a Cinelli? What wisdom is there about open bottom brackets. Graeme was talking about lining it to seal it.

Tim Linford

There is no point in sealing a bottom-bracket. A frame is less likely to rust if its bottom-bracket is able to drain any water that may get into it via breather holes, bottle boss threads etc. The bottom-bracket shell itself may be more rusty in the very open Cinelli style, due to the relatively free passage of dirty water in and out, but the bottom-bracket shell is comparatively thick and any rust can be seen and treated. As for the bearings, in modern units (except in rare and unusual designs) they are sealed from all sides and so it does not matter if the weather can get at them from all sides. In fact, a bottom-bracket that does not drain is more likely to subject the bearings to total immersion, which is more likely to defeat the seals.

So leave this bottom-bracket as is, but treat the inside of the bottom-bracket with rust-preventing paint and/or wax-oil. And choose bottom-bracket/crankset designs where the outermost parts inside the bottom-bracket are aluminium or rust-proofed steel, or paint them before fitting, and use a rust-preventing anti-seize compound on the threads.

Chris Juden

 

This was first published in the October / November 2014 edition of Cycling UK's Cycle magazine.

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