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  1. #1
    Fat-tired Roadie
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    Nov 2007
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    Shimano M-570 chainring on Shimano FC-M341 crankset

    I started having trouble shifting from my middle to my small chainring after getting a new chain, so I used my REI dividend to pick up a new middle chainring. On trying to bolt it onto my crankset, a Shimano FC-M341, which I think is about Acera level, I bent it. Looking closely at the way the chainring sits on the crank spider, I notice that the chainring has flats on it that look like they're supposed to sit on the arms of the spider. These flats are narrower than the arms on my crankset.

    I have a couple ideas as to how to solve this poblem, and I would like to hear people's thoughts on the best way to go.

    I think the simplest solution is to put some washers between the new chainring and the crank spider so that it doesn't put pressure on the raised sections of the ring next to the flats. I'm concerned that messing with the spacing this way might screw up my shifting, although the difference is less than a millimeter. It occurs to me that I might solve this, somewhat, by spacing the small chainring out an equal amount, to preserve the small-middle spacing. I'm more concerned with preserving the relationship between the two smaller rings. My big ring is pretty much a bashguard anyway if I'm not on the road.

    I may be able to fast-talk REI into exchanging for a different ring, that has simpler machining and doesn't have this problem. I don't really care about an aesthetic match, but the shop guy said the Shimano ring had better wear-life and shifting performance than the FSA ring. I don't know if they carry other brands. They are the "Return Every Item" club.

    I can stick my old chainring back on and live with it. Obviously I don't want to do this.

    A new crankset is currently out of the question. I'm too broke.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  2. #2
    Fat-tired Roadie
    Reputation: AndrwSwitch's Avatar
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    Nov 2007
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    Just got back from REI - I figured they'd have both washers, other chainrings, and a cash register if I just bagged the whole project and returned the one I bought.

    The shop technician said he'd never seen anything quite like what I showed him. Sorry I didn't take a picture. While he seemed to think that spacers might work, he decided to exchange my Shimano ring for an FSA ring.





    Of course the true test is whether or not that shift will work under load and dirty.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

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