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Thread: Making chainrings run true..

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    Default Making chainrings run true..

    So, I've got a crankset and chainrings i'm pretty happy with, except that they don't run true. Makes it impossible to fully avoid chain rub at the extremes and means you can choose between chain rub and you're chain catcher, you know, catching your chain.

    I haven't measured to see if it's just the chainrings or the crankset itself.

    If it's just the chainrings do you just apply leverage and force? Is there a magic technique? Is there a "Whatever you do, DON'T do this"

    If it's the crankset - is that just SOL or is there an approach for that too?
    Colin Mclelland

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    Default Re: Making chainrings run true..

    Depends! Are you concerned with run out or roundness? Run out can be the crank arms, either the chainring seat faces or the arms themselves. If it is the arms good luck with that. You can have some luck futzing with the faces and using nominal spacers. Chainrings themselves generally speaking do not have run out issues.

    Roundness is a fun one. On a track bike, no rear mech to take up chain slack, roundness is easy to spot...just spin the cranks slowly and check for chain tight/slack. The way you "fix" this is a delight. Simply loosen the chainring bolts enough that they are finger tight and find where the chain is the most tight. On a track bike just squeeze the top and bottom portions of the chain together and re-check. On a road bike use a soft hammer to tap tap tap the chainring highspot and recheck. This operation will move the chainring a tiny amount to the negative. I've had very good luck with this method for track bikes and tandem timing chains. Road bikes really do not matter.

    How we doin'?
    Last edited by Too Tall; 03-19-2020 at 07:36 AM.

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    Default Re: Making chainrings run true..

    Have you tried taking off the chainring and resting it on a flat surface to see if it's "bent"?
    Chikashi Miyamoto

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    Default Re: Making chainrings run true..

    Quote Originally Posted by Too Tall View Post
    Roundness is a fun one. On a track bike, no rear mech to take up chain slack, roundness is easy to spot...just spin the cranks slowly and check for chain tight/slack. The way you "fix" this is a delight. Simply loosen the chainring bolts enough that they are finger tight and find where the chain is the most tight. On a track bike just squeeze the top and bottom portions of the chain together and re-check. On a road bike use a soft hammer to tap tap tap the chainring highspot and recheck. This operation will move the chainring a tiny amount to the negative. I've had very good luck with this method for track bikes and tandem timing chains.
    I wish someone had told me that years ago!! I know what to do now. Thanks!
    Chikashi Miyamoto

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    Default Re: Making chainrings run true..

    Quote Originally Posted by Chik View Post
    I wish someone had told me that years ago!! I know what to do now. Thanks!
    Welcome. Can't take full credit I learned this from the longbeards at Trexlertown Track.

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    Default Re: Making chainrings run true..

    Quote Originally Posted by Too Tall View Post
    Depends! Are you concerned with run out or roundness? Run out can be the crank arms, either the chainring seat faces or the arms themselves. If it is the arms good luck with that. You can have some luck futzing with the faces and using nominal spacers. Chainrings themselves generally speaking do not have run out.

    How we doin'?
    Run out. I was curious between spacers and ďbendingĒ.
     

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    Default Re: Making chainrings run true..

    Quote Originally Posted by Colinmclelland View Post
    Run out. I was curious between spacers and “bending”.
    Wheels MFG aka QBP makes .6mm chain ring spacers, I had to fix the chain line of an Sugino OX crank with them.
     

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    Default Re: Making chainrings run true..

    Quote Originally Posted by Scott G. View Post
    Wheels MFG aka QBP makes .6mm chain ring spacers, I had to fix the chain line of an Sugino OX crank with them.
    Thank you! Iíve got the slightly bizarre situation that having taken the chain off everything seems fine, but for example, i had to run a chaincatcher so far away that it actually didnít. See what today brings!
     

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    Default Re: Making chainrings run true..

    Modern chainrings are usually made of 7xxx series or heat-treated alloy, those materials do not like to be manipulated after production, so don't try to readjust them unless you want them to crack.

    The new 11 & 12sp gear setups are little tolerant to imperfections in the chainset spider or the chainrings, so any side wobble can be a nuisance.
    Any good workshop should keep a sheet of 0.10mm stainless steel to fabricate shims when needs to. I have a hole-puch that is useful for htose things (though it's not easy to punch a hole is such thin material)
    Andrea "Gattonero" Cattolico, head mechanic @Condor Cycles London


    "Caron, non ti crucciare:
    vuolsi cosž colŗ dove si puote
    ciÚ che si vuole, e piý non dimandare"

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