Speed Trumps Durability.

I’m a bit of a nut when it comes to my drivetrain and I really hate drag. Recently, drivetrains have made a lot of strives in performance, mainly with new crank and BB designs, which are really awesome compared to the old Topline cranks with square taper BB I used to use (and send back regularly from warping the spider every couple months…). But this performance has come at a cost, friction.
And I really hate friction.
My friend over at B&L Bikes, Gordon was showing me how smooth the new Campy Super Record 11 (drool) was. And it is… Which gave me a bit of spin envy. My Shimano BB in my MTB is nowhere near as smooth. Well, it’s smooth, but has a lot of drag.

I’m a bit of geek (I was the Grand Champion for model rocketry at the state fair in CO way back…) and like to take stuff apart, usually making the thing broken at some point in the process, so I sometimes wait till it’s on its last legs to begin.

I do not recommend you try any of what I am about to describe.

I’ve had this Shimano BB a while and decided to fool around with it after I got home since the Sprout was sleeping. I pulled the cranks and took a look at it. In bold letters are the words “Do Not Disassemble”. Well, that’s right up my ally. Starting is the scary part. When you pull off the cranks, you see a large plastic plate on either side of the BB which are what the cranks snug up against, sort of like a headset. I wasnt sure how those plates were attached. Turns out they just snap in, really securely. I was able to pop them off by tapping the inside lip (from inside the BB shell) out from the backside with a screwdriver and hammer (gentle persuasion…).

Once I did that, I could see the cartridge bearings, which look just as you would suspect. Just like an oversize skateboard bearing. They still felt very smooth and ran a lot better without the plastic plates, but the plastic plates appeared to be important as spacers for the cranks, so I wanted to use them. I found a small O-ring that seals around the outer perimeter of the plate to help keep dirt out. Well, that’s gotta go… Then I popped the dust seal off the cartridge bearings, lubed the bearings with some low viscosity oil and then just popped the plastic plates right back on. No dust seals. For the dry climate we have around here, all we have is dust, water contamination is rarely an issue, and the plastic plates are snug enough that it will probably be OK, at least for a few races… If I were more worried about longevity, I would have left the large seals on the cartridge bearings. I think most of the drag was coming from the small outer O-rings, but I’m not that worried about longevity.

The o-rings and seals I removed from my BB.

The o-rings and seals I removed from my BB.

Now my $30 shimano BB runs as smooth as your fancy $300 ceramic BB, and I still have beer money.


One Response to “Speed Trumps Durability.”

  1. elewinnek Says:

    You know, I thought I was educated and intelligent and all, but I really don’t know what you’re talking about.

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