Front sprocket rubbing against frame

roverthehill
roverthehill Posts: 155
edited December 2011 in MTB workshop & tech
Hi,
pretty new to MTBs so apologies if I get the terminology wrong lol. On my old bike, the front inner sprocket has started to rub against the frame - kinda acting like a circular saw... I noticed it straight away so no real damage done to the sprocket or the frame.

Is it possible to adjust the sprockets so they don't rub or is there something more sinister wrong?

I've bought a new Sunn but I wanted to use this harlem for commuting.

Cheers

Comments

  • nicklouse
    nicklouse Posts: 50,675
    so what have you changed?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • roverthehill
    roverthehill Posts: 155
    nothing has been changed - I was just out on a trail, when I noticed a scraping sound. As I said the lower inner sprocket/cog is rubbing against the part of the frame that runs out to the rear sprocket.
  • nicklouse
    nicklouse Posts: 50,675
    then something is worn out. like the BB or it is incorrect. but as it fine before i would say the former.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Anonymous
    Anonymous Posts: 79,667
    Front inner sprocket as in the inner (granny) chainring?

    Chainring bolts come undone and it's err, come loose or something (surely would just be rattling around and the chain would jam or snap)? Hmm weird.

    Not sure how a worn BB would cause it to rub against the frame. Only thing I can think is it was never right in the first place and something's happened to make you notice.

    Pictures?
  • The Rookie
    The Rookie Posts: 27,812
    So your not sure how worn bearings allowing the axle to move side to side would allow a sprocket that has minimal clearance to then touch the stay - well I'm convinced!

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Anonymous
    Anonymous Posts: 79,667
    Well maybe, but it would surely be so obviously moving a lot and you'd have gone past the point of noticeably shagged bearings with wobbly/grinding cranks where you could have done something about it.

    Also a granny with so little clearance? ! If you're running a large middle ring on the granny then maybe but seems unusual.

    Seems something is set up wrong and/or poor frame design to allow it to do that.
  • austy
    austy Posts: 5
    Can I just provide my two penneth worth.

    What type of bottom bracket does the OP have is it a press fit like BB30 style, cartridge style (shimano octalink) or external??

    I have seen these slide out of position placing the chaing rings away from the bottom bracket but could easily go the other way.
  • The Rookie
    The Rookie Posts: 27,812
    Given the OP's description I'll guess its a square taper and probably cup and cone....

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.

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