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Connundrum: Bottom Bracket causing crank wobble?

  • 18-07-2013 10:53pm
    #1
    ChainWhip
    Registered Users, Registered Users 2 Posts: 225 ✭✭


    So I'm stripping a frame and transferring everything to a new frame.

    I was trying to get the front derailleur correctly lined up and noticed that the chain was rubbing the derailleur at a certain point of each revolution, just inside the crank arm.

    Great I thought, a bent spider or a bent chainring. So I took off the chainring and it seemed in line i.e. no bend. I reattached the crank at 180 position to where I originally had it and the rub had switched to the opposite side of the chainring.

    Eureka I shout, it's not the crank, it must be bottom bracket that's shot (it's a second hand bb - dunno how many miles it's done). I took out the BB and it has some play in it but as its the first time I've removed one I don't know how much movement is the norm.

    Does it seem plausible to anyone else that a bb could be causing the wobble?

    Thanks :)


Comments

  • #2
    dermo1990
    Registered Users, Registered Users 2 Posts: 215 ✭✭dermo1990


    I've had this exact issue with two bottom brackets, so if there is any play whatsoever in the BB, then it needs to be replaced, otherwise the problem will just get worse. Typically a BB should have no play (well that's my experience from square taper ones anyway, probably the same for BB30, etc.). In both cases of my BB being replaced, the play I had in the cranks was gone after a new BB was fitted, so the worn BB was causing the wobble.


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