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  1. #1
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    Only a few chain links are rubbing against the FD

    Hi,

    A few chain links (~4-5) are rubbing against the outer cage when on the largest chainring. Upon closer inspection, these few chain links did not have the clearance that other chain links had.

    While I was trying to put the rear wheel on in the wrong gear (largest chain ring + 8th cog or so), the a portion of the chain basically fell off the largest chainring and got stuck between the FD cage and the largest chainring. I had to loosen the FD cage so I could increase its height in order to get my chain back on the largest cog.

    Anyways, I'm thinking those few chain links that were stuck between the cage and the largest cog might have bent slightly. This is just my guess. These few chain links seem to run fine when it reaches the RD though.

    Is this just bad FD tuning or could the chain links have been slightly bent? Note again that the FD rubbing only happens on a few chain links and not the entire chain.

    Thanks for the help!

  2. #2
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    The rings are way softer than the chain so it is way more likely that you bent the large chain ring. Check if the rub corespondents to the position of the crank arm to confirm that it is the ring. With luck it is slight enough to simply adjust the FD with the limit screw to eliminate the rub. After you may be able to re-true the ring. I wont say that I recommend doing this but I once straightened a bent chain ring mid ride using a rock as a hammer. It came back into true so well that I couldn't find any more bend in it once I got home.

  3. #3
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    I agree with faceplant, it is much more common (likely?) that the big ring has bent teeth rather than the chain being physically different in spots. I actually haven't even seen a chain that wasn't damaged which had a variation which would cause it to hit the FD. Sometimes it is very difficult if not impossible to adjust a FD to the point where it will not rub in some gear combinations. You shouldn't adjust your FD to compensate for your chain drop during your rear wheel install, that's probably just a one-off sort of issue and has no bearing on how things behave while riding. Park Tool has a great write up on adjustment if you're looking for tips.
    Don't you hate it when a sentence doesn't end the way you think it octopus?

  4. #4
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    Hmm... it doesn't seem like the large chainring is bent. The rubbing only happens on smallest cog, and I heard that occasional rubbing is normal since the frame bends as you pedal or something. On larger cogs, the problem is almost non-existent.

  5. #5
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    Shift the FD to the outer ring and check that the outside of the FD cage is parallel with the chain line. If its lined up and you still rub the outside of the cage you could try a turn or two on the barrel adjuster to pull the FD slightly more to the outside.

  6. #6
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    Quote Originally Posted by BobaX View Post
    Hmm... it doesn't seem like the large chainring is bent. The rubbing only happens on smallest cog, and I heard that occasional rubbing is normal since the frame bends as you pedal or something. On larger cogs, the problem is almost non-existent.
    If it's on the small ring it's probably just a limit adjustment or cable tension adjustment. But again, in some gear combinations the rubbing is just something you'll have to deal with.
    Don't you hate it when a sentence doesn't end the way you think it octopus?

  7. #7
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    Thanks for the suggestions guys, I will check it when I get home.

    Will this rubbing cause premature wear on the chain or cogs/chainrings?

  8. #8
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    Quote Originally Posted by BobaX View Post
    Thanks for the suggestions guys, I will check it when I get home.

    Will this rubbing cause premature wear on the chain or cogs/chainrings?
    No, but it is important to understand how to identify a worn chain so you can prevent costly frequent drivetrain replacements.
    Don't you hate it when a sentence doesn't end the way you think it octopus?

  9. #9
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    On occasion, I've twisted or bent a link and this ended up misaligning the subsequent few links; kind of puts them 'out of square'. The link closest to the twisted link would be the worst, then the effect lessens as you get further away. Need to either remove/replace the tweaked link, or replace the entire chain. This isn't all that likely though. Sometimes, certain gear combos just rub.

    If the rubbing is really minor and you can't seem to adjust the tension and limit screws enough to get rid of it, you can always try the 'bend it into shape' method. I've found derailleur cages to be pretty amenable to a little tweaking. Of course, a lot depends on your comfort and ham-fisting skill level.

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