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Eccentric chainwheel

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  • 21-10-2008 9:07am
    #1
    souter
    Registered Users Posts: 634 ✭✭✭


    No, I don't mean it wears a cravat and slippers during the day, instead my fixie chain is tight at one crank location, loose at another.
    Needless to say Sheldon Brown addresses this , but after several goes I've only managed to improve the tension marginally.
    I also can't see much play at all in the stackbolts.
    So I was wonderring
    a) could there be other causes
    b) should I should keep trying
    c) will most bike shop mechanics be competent with single speed gears?


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    #2
    Gavin
    Registered Users Posts: 4,676 ✭✭✭Gavin


    This is a serious problem with my singlespeed, a warped chainring. It derails if the chain tension isn't high and I hit a bump at the wrong time. I'm just going to get a new chainring.


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    #3
    souter
    Registered Users Posts: 634 ✭✭✭souter


    Ta Verb, but I don't think it is warped - the chain doesn't ever come off, it just makes an annoying "whirr-whirr" sound that it didn't use do. It also looks true if I up end the bike and spin it.
    Plus I've been pretty careful with it. The only bumps it's had are a few times wheeling it down big steps where the bottom of the chainwheel struck the riser.
    I wondering if I could have worn the chainwheel already (6 months/2000 miles tops)? Given the tightest is with the left crank at pointing forward and horizontal, the slackest is where I'm pushing off in a big gear.
    I'll try rotating the chainwheel relative to the cranks tomorrow.


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    #4
    souter
    Registered Users Posts: 634 ✭✭✭souter


    Ok, rotated the chainring and the tight spot rotated as well. So it's the chainring. Also noticed it appears to be aluminium, so new (steel) chainring would appear to be in order.
    Whoever said fixies were low maintenance?


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    #5
    niceonetom
    Registered Users Posts: 4,833 ✭✭✭niceonetom


    i don't think you can make a chainring become eccentric through use - wear only affects the tooth profile, and does so all the way around the circumference. the chainring was probably always slightly out and perhaps took a knock at some point?

    fwiw the highest quality chainrings are made out of aluminium - i have a specialités chainring (130bcd) that has done many thousands of k shows very little wear.


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    #6
    souter
    Registered Users Posts: 634 ✭✭✭souter


    Cheers Tom, I'll defer to your knowledge on this matter. Looking for a steel chainring does indicate they are a bit of a niche, and mainly for the smaller sizes.
    Still puzzled as to how it could have have become ovoid without warping, though the few knocks it has had are from striking the bottom off the ring directly off steeper than expected steps.
    Anyway,I'll get a new (alu) one.


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