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  1. #1
    Join Date
    Mar 2010
    Posts
    209

    Cranks/Bottom Bracket

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    I recently completed a build-a-bike class wherein we took apart an old bike, cleaned it up, replaced parts and put it back together. It was fun, 2 people per bike and they were old bikes. Mine was a Nishiki, shifters on the downtube type.

    To check our work on the bottom bracket we had to tug at the cranks and feel for play, rotate the cranks and feel for smoothness and then let the pedals swing like a pendulum (all without the chain attached of course.)

    In recent weeks I've noticed my road bike is hard to pedal sometimes. I've tried lubing the chain, check brake sticking, wheel, shifting, and all seems ok. After this class I started thinking about the bottom bracket, even though I don't hear any creaks or other sounds.

    My question: Is doing the crank pendulum swing check applicable to a 2008 carbon bike? Or am I comparing apples to oranges? When I did it, the cranks did not move unless I pushed/pulled them. Not stiff but no swing. And, no chain so there was less resistence in checking. Is this normal? Oh, I checked for the type of bottom bracket and all I could find was Shimano Ultegra.

    Thanks!
    dt

  2. #2
    Join Date
    Sep 2007
    Location
    Uncanny Valley
    Posts
    14,645
    I don't have any specific knowledge of modern BBs, but bearing relationships are bearing relationships, and from free ball bearings in an old-style hub to the needle bearings in a motorcycle steering stem, they're all checked the same way. The part should move freely but without any play outside the intended plane of travel - just as you describe.

    It's not a big deal to either hold the chain aside to check your BB, or to just do it routinely when you replace the chain.
    Speed comes from what you put behind you. - Judi Ketteler

  3. #3
    Join Date
    Jan 2011
    Location
    Austin, TX
    Posts
    212
    Correct me if I'm wrong, but you checked the cranks with the chain off, right? If so, the cranks should swing freely and smoothly. If they don't, you probably need to replace the bottom bracket ...because I don't think most modern bottom brackets are reparable (ie, can be taken apart, cleaned, and regreased).
    JEAN

    2011 Specialized Ruby Elite - carbon fiber go-fast bike
    DiamondBack Expert - steel road bike
    Klein Pinnacle - classic no-suspension aluminum MTB

  4. #4
    Join Date
    Mar 2010
    Posts
    209
    Thanks Oak and Silver, that's what I thought.

    Silver, yes I did check it without the chain on. And yes these type of BB have to be replaced. Bummer.

    dt

  5. #5
    Join Date
    Dec 2010
    Location
    Boise Idaho
    Posts
    1,192
    okay, I ask the Bike Hermit and read him your question. He said as long as it isn't binding or making noise it sounds like it is fine. Is probably a BB with outboard bearings and they are stiff.

    I am sure you checked, but are your tires inflated enough
    Sky King
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  6. #6
    Join Date
    Mar 2010
    Posts
    209
    Sky King, thank you for asking! Yes, I always make sure the tires are properly inflated. Besides big thorns there are a lot of little, broken pieces of thorns on the roads. Sometimes those little punctures don't show up until after the ride. Regular tire checks are a must around here.

    No noise. Only when the chain is on and it has a small grinding noise. But I have figure out it is sand and a gentle hosing with water, wipe down and after it dries a relube. Seems to take care of that. The roads have a lot of sand, especially this time of year (monsoons).

    What exactly do you mean by "isn't binding"?

    Thanks!
    dt

  7. #7
    Join Date
    Apr 2009
    Location
    California
    Posts
    371
    Quote Originally Posted by Desert Tortoise View Post
    What exactly do you mean by "isn't binding"?
    "Binding" means that it stops turning, or gets very hard to turn. Thus, "isn't binding" means the crank spins all the way around without encountering (major) resistance along the way.
    Laura

 

 

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