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Thread: Chain Problems

  1. #1
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    Chain Problems

    Recently after my last ride I noticed my chain skipping/jumping under hard pedaling. It only does it on the 2nd front chain ring in any gear. I flipped the bike over and pedaled through and noticed the chain was releasing late on one of the teeth. Is it likely that it is bent because it doesn't appear to be, and I know that the teeth are supposed to be offset from each other. Derailleur problem? Any info is appreciated.

  2. #2
    NOT a weight weenie Hunter's Avatar
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    Check the rear der. pulleys and make sure they are in line with the rear cogs. If they go to the right then turn the the barrel adjuster to the left until it is in line, and vice versa. Do this with the bike upright. See if that does it.

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    Thanks, will try that.

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    Honorable Member beowoulfe's Avatar
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    Your transmission is shot. You probably need a new chain and rear cassette/freewheel.

    The best way to determine whether a chain is worn is
    by measuring its length. A new chain has a half-inch
    pitch with a pin at exactly every half-inch. As the pins
    and sleeves wear, this spacing increases and this
    concentrates more load on the last tooth of engagement,
    changing the tooth profile. When the chain pitch grows
    over one half percent, it is time for a new chain. At one
    percent, sprocket wear progresses rapidly because this
    length change occurs only between pin and sleeve so
    that it is concentrated on every second pitch; the pitch
    of the inner link containing the rollers remaining
    constant. By holding a ruler along the chain on the
    bicycle, align an inch mark with a pin and see how far
    off the mark the pin is at twelve inches. An eighth of
    an inch (0.125) is a little over the one percent limit
    while more than a sixteenth is a prudent time to get a
    new chain.

    prockets do not change pitch when they wear, only
    their tooth form changes. The number of teeth and base
    circle remain unchanged by normal sprocket wear.

    A new chain often will not freely engage a worn rear
    sprocket under load, even though it has the same pitch
    as the chain. This occurs because the previous (worn
    and elongated) chain formed pockets in the teeth by
    exiting under load. A chain with correct pitch cannot
    enter the pockets when its previous roller bears the
    previous tooth, because the pocket has an overhang that
    prevents entry.

    Without a strong chain tensioner or a non-derailleur
    bicycle, the chain has insufficient force on its slack run
    to engage a driven sprocket. In contrast, engagement of
    a driving sprocket, the crank sprocket, generally
    succeeds even with substantial tooth wear, because
    The drive tension forces engagement.

    However, worn teeth on a driving sprocket cause
    "chainsuck", the failure of the chain to disengage the
    chainwheel. This occurs more easily with a long arm
    derailleur, common to most MTB's, that is one
    Reason this occurs less with road racing bicycles, that
    experience a noisy disengagement instead.

    In contrast a worn chain will not run on a new driving
    sprocket. This is less apparent because new
    chainwheels are not often used with an old chain. In
    contrast to a driven sprocket (rear) the chain enters
    The driving sprocket under tension, where the previous
    chain links pull it into engagement. However, because
    a used chain has a longer pitch than the sprocket,
    previous rollers bear almost no load and allow the
    incoming chain link to climb the ramp of the tooth,
    each successive link riding higher than the previous
    until the chain jumps. The pockets in a used sprocket
    are small but they change the pressure angle of the teeth
    enough to overcoming this problem.

    Jobst Brandt <jobst.brandt@stanfordalumni.org>


    Beo
    Greenspeed GTO 1027

  5. #5
    NOT a weight weenie Hunter's Avatar
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    Originally posted by beowoulfe
    Your transmission is shot. You probably need a new chain and rear cassette/freewheel.
    Beo
    If it only happens in one ring? He did say only in the middle ring. he did not state that the chain had been recently replaced without replacing the cassette or freewheel. So before buying and replacing, checking and adjusting should be done first.

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    If the chain skips teeth on a given cog or cogs,it is usually chain or cog wear.If the chain skips from cog to cog is is typically cable tension,but in a worst case it could also be caused by bad cassette/freewheel. One needs to know how to measure chain to evaluate that possibility. new chain measures exactly 12" in one foot of chain,c-c of pins.Replace when the chain under tension measures 12 1/16".

  7. #7
    Senior Member mechBgon's Avatar
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    The symptom sounds like my experiences with a worn-out middle ring, or else a ring with at least one damaged tooth that throws the chain off.

    If your ring is shot, investing in a good, thick 7000-series middle chainring will probably pay off in the long run. I've been using the 7075 Real Design rings and they have remarkable durability (click me). If you buy Real, you want the "Ultimate" model, since those have the hard 7075 aluminum and the nickel plating.

  8. #8
    Honorable Member beowoulfe's Avatar
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    I've found that if you've let your chain go without proper maintainence and it's worn out,
    it probably has taken the cassette/freewheel also. Nature of the beast.
    Greenspeed GTO 1027

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    Got the problem fixed. Turned out that the middle chainring in the front was bent. Nothing a couple of minutes with a hammer couldn't fix. All is well now.

  10. #10
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    Originally posted by Rick LV
    Got the problem fixed. Turned out that the middle chainring in the front was bent. Nothing a couple of minutes with a hammer couldn't fix. All is well now.
    you didnt notice this at first? this was the first thing i noticed when my friend's bike had problems..

    and how does hammering the ring back into shape compare to getting a new ring altogether? my friends was bent pretty bad and the shop hammered it back into shape, i thought they'd toss on a new ring for him though.
    i won't deny it i'm a straight ridah

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