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Crank rubbing against front mech?

manick0decpmanick0decp Posts: 190
edited June 2007 in Workshop
I've noticed my crank making contact with the outside plate on the front mech when I'm in the big ring of my tripple chainset?

Posts

  • pbiggspbiggs Posts: 9,232
    You need to adjust the mech's limit screw, or the angle of the mech, or both.

    <i>~Pete</i>
    <i>~Pete</i>
  • manick0decpmanick0decp Posts: 190
    Mech rotation, height and limit screw is fine. All perfect in fact. The crank is secure aswell.
  • nmcgannnmcgann Posts: 1,780
    <blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by manick0de</i>

    Mech rotation, height and limit screw is fine. All perfect in fact. The crank is secure aswell.
    <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

    Unless your BB bearings are shot or the ring is bent then see Pete's email again.

    Neil
    --
    "Because the cycling is pain. The cycling is soul crushing pain."
  • pieintheskypieinthesky Posts: 417
    First try adjusting your top limit screw until the mech does not hit the crank. If you can do this and can still change gear ok and the chain doesnt rub the mech plate (particularly in top gear) then problem solved.

    If this doesnt work maybe your mech isnt set right. Check that the outer mech plate is parallel to the chainring and is set at the right height then try again as paragraph above.

    Are you using a mixture of components (groupsets or manufacturers), you might have a compatibilty problem.

    I have recently resolved a similar problem with a campag Centaur front mech by bending the curved rear section of the outer plate so that it was flat and parallel with the rest of the plate. This allows the mech to move out further before hitting the crank.

    Hope this makes sense and helps.
  • pbiggspbiggs Posts: 9,232
    <blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by manick0de</i>

    Mech rotation, height and limit screw is fine. All perfect in fact. The crank is secure aswell.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">I suspect you need to rotate the mech so the rear end is further in, even if does look fine to you at the moment.
    <i>~Pete</i>
  • manick0decpmanick0decp Posts: 190
    Really eveybody settings are all fine. Two bike shops have confirmed this and bike needs to be booked in so they can have fiddle with it but they're not free for a couple of weeks.

    Height - No effect on the problem.
    Rotation - The mech is runnung near parralel with the swing of the crank so it rubs all the way along the mech.
    Limit screw - It can be ajusted not to make contact but there s severe chain rub with the mech actually chainging the angle of the chain. I'ts currently adjusted so the crank can just clear the mech but I have to put up with a certain amount of chain rub when using the three smallest sprockets.
  • d_c_h_wd_c_h_w Posts: 31
    I had this problem when I upgraded my veloce 9s chainset to a centaur 10s. The crank arm on the 10s is noticeably closer to the chainring. I ended up changing the front derailleur to a 10s spec one, as this had a flatter outer plate
  • pieintheskypieinthesky Posts: 417
    It sounds like your mech and cranks are incompatible, What are they?
  • manick0decpmanick0decp Posts: 190
    Bontrager cranks and Shimano mech. Sounds like I've got an excuse to upgrade my chainset?
  • pbiggspbiggs Posts: 9,232
    <blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by manick0de</i>

    Really eveybody settings are all fine.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Unless the mech is broken or bent in some peculiar way, the settings by definition are NOT fine if you are not able to use the smallest three rear sprockets with the largest two chainrings without crank rub.

    Forget the bike shops and get your allen key and screwdriver out, is my advice. It can be tricky to get a triple mech working nicely, and what looks fine might not be what's best overall really. So be patient and try tiny adjustments at a time. Pay attention to cable tension as well as everything else.
    <i>~Pete</i>
  • pbiggspbiggs Posts: 9,232
    Ok, maybe this combo of components is incompatible, but still I'd have one more go at adjusting just to make sure.
    <i>~Pete</i>
  • monty_dogcpmonty_dogcp Posts: 382
    You haven't bent your crank arm? As Pete says - correctly set-up a front mech outer plate should be well clear of the crank arm.
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