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Chain coming off crankset

  • 24-03-2016 8:11pm
    #1
    mrcheez
    Registered Users, Registered Users 2 Posts: 14,074 ✭✭✭✭


    I have a 20-speed crankset (2 rings) and lately when I change onto the larger ring the cable over-extends and the chain falls onto the pedal.

    I dropped into the bike shop where they adjusted the chainguide screw but it's still happening.

    Has the cable overstretched, or what else should I ask them to look for?


Comments

  • #2
    ted1
    Registered Users, Registered Users 2 Posts: 23,893 ✭✭✭✭ted1


    mrcheez wrote: »
    I have a 20-speed crankset (2 rings) and lately when I change onto the larger ring the cable over-extends and the chain falls onto the pedal.

    I dropped into the bike shop where they adjusted the chainguide screw but it's still happening.

    Has the cable overstretched, or what else should I ask them to look for?
    How many miles on the rings? They could be worn down.


  • #3
    mrcheez
    Registered Users, Registered Users 2 Posts: 14,074 ✭✭✭✭mrcheez


    ted1 wrote: »
    How many miles on the rings? They could be worn down.

    The larger ring? Only had it changed a week ago.

    Seemed to start yesterday when I gave quite a firm press on the gear shifter, so made me think I might have stretched it.


  • #4
    cython
    Registered Users, Registered Users 2 Posts: 4,792 ✭✭✭cython


    By rights if the limit screws are set correctly, it shouldn't matter how hard you hit the lever, the chain should never be thrown over the big ring - the upper limit screw should literally stop the cable from being able to be pulled that much. Similarly if all tension is removed, a correctly adjusted lower limit screw should never allow the derailleur and thus the chain to drop further in than the small chainring.

    Additionally, an overstretched cable would actually result in a chain being sluggish to shift up into the big ring, due to insufficient tension to pull the derailleur "out" - if anything the cable is too taut by the sounds of it.


  • #5
    Craig06
    Registered Users, Registered Users 2 Posts: 430 ✭✭Craig06


    The front mech will only push the chain as far as the limit screws will allow it. Sounds like your limit screws are not adjusted correctly


  • #6
    MarcinG
    Registered Users, Registered Users 2 Posts: 356 ✭✭MarcinG


    Check chain carefuly by rotating crank backwards if you can. Or forward on the stand. Check if Your chain joint (if you using traditional push pin for it) is not fully stretching to shape of rings. Maybe cage of yor front mech is so loose that it can no longer work properly. Check all rings and mech carefully. Im asuming it worked before and you not using mix groups of different makes. I had similar thing with rear mech once under pressure it will keep switching gears back and forth but during casual ride in the park it would work ok. I had a cracked cassette which was flexing under pressure and dropping gear. It took me weeks to find it as it was springing back to shape.


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  • #7
    smacl
    Moderators, Society & Culture Moderators Posts: 15,812 Mod ✭✭✭✭smacl


    mrcheez wrote: »
    The larger ring? Only had it changed a week ago.

    Did you change the chain at the same time? Could be a stretched chain not meshing well with the new ring. I'd usually change both at the same time.


  • #8
    mrcheez
    Registered Users, Registered Users 2 Posts: 14,074 ✭✭✭✭mrcheez


    smacl wrote: »
    Did you change the chain at the same time? Could be a stretched chain not meshing well with the new ring. I'd usually change both at the same time.

    Chain was changed about 2 weeks ago :)

    It must be the limit screws.. in the shop's defence they were closing within a few mins of me arriving so didn't really have too much time to play around with it.


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