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  1. #1
    Senior Member bellweatherman's Avatar
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    Safe to file down a chainring?

    This is really frustrating. My outer chainring is a 110BCD. My middle chainring is a 110BCD. I am using a MTB triple crankset on a fixed bike with one ring. I am trying to improve my chainline, by moving the outer ring to the middle position, but it won't fit.

    Both rings use a BCD diameter of 110. Shimano has proprietary rings such that a MTB outer 110BCD ring is not the same shape as a MTB middle 110BCD ring. Therefore, a 110BCD outer ring will not fit in the middle position both rings are 110BCD. Hypothetically, you could go out and buy a 42T outer ring for a Shimano MTB crank and try to use it in the middle position, only to find that it won't fit in the middle position.

    Is it safe to file down a small bit of the chainring near the bolt hole so that it fits on the crank? For example, I want to file the parts of the spider furthest to the inside of the chainring, but being careful not to file any part of the hole.
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  2. #2
    yo yo yo yo yo
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    go for it

  3. #3
    Senior Member calf man's Avatar
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    You might be better off filing the spider crank instead of the chain ring.
    The small amount of metal between the hole and inside edge of the chain ring is critical for the strenth of that part, and by filing that area, you could end up with a chain ring that look like an old record that you left on the dashboard of your car on a hot day.

  4. #4
    steel lover
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    I think you'd be fine... the bolts will keep the ring centered up just fine. Never done it though.

  5. #5
    raodmaster shaman
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    so if i get what you are saying the shimano rings are squared off on the inside of the ring which is keeping them from mating up to the rounded lands on the crank?

    i never knew this was an issue, but i dont see why it would matter to just knock that little bit of metal off.

    edit: ill second removing it from the crank first. it has more metal to wrok with.

  6. #6
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    Buying the proper part sounds easier.

  7. #7
    Yup pyze-guy's Avatar
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    Shorter b/b.
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  8. #8
    Senior Member BoozyMcliverRot's Avatar
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    just but a SS ring with the same BCD.........nuff said.
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  9. #9
    Senior Member bellweatherman's Avatar
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    Quote Originally Posted by BoozyMcliverRot
    just but a SS ring with the same BCD.........nuff said.

    You have no idea. You can't just assume that because the ring you are buying will fit just because it is the same BCD as the one you are replacing. Maybe try reading the original message.
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  10. #10
    Senior Member bellweatherman's Avatar
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    Quote Originally Posted by roadgator
    so if i get what you are saying the shimano rings are squared off on the inside of the ring which is keeping them from mating up to the rounded lands on the crank?

    i never knew this was an issue, but i dont see why it would matter to just knock that little bit of metal off.

    edit: ill second removing it from the crank first. it has more metal to wrok with.

    That's kinda what I'm saying. See the above pic for reference. On this particular MTB crank (Deore), the 110 BCD Shimano Outer Ring has a little bit more metal around the hole than a 110 BCD Shimano Middle Ring. The way Shimano designs the crank, they force you to buy a 110 BCD Shimano Middle Ring as no other 110 BCD ring will fit in the middle position.

    You think I should remove material from the shoulder/spider area of the crank instead of the chainring? I was going to file the chainring since it seems less drastic, ie. I would be altering a chainring as opposed to a crank.

    PS- No BB spindle (other than a hypothetical 68x98) is short enough for me to move the outer ring in far enough to obtain a perfect chainline (52mm MTB fixed). The only solution is to have the big ring on the middle position using a 68x113mm BB which yields a perfect 52mm chainline.
    Livestrong. The personal fundmaker of Lance Armstrong. The company who are in business to not donate to cancer research, but only to inform people that cancer is bad.

    Armstrong. The man without integrity, no care for the sport, and no problem with testing positive for EPO and making donations to cover it up.

    01101010101010001010

  11. #11
    mofo
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    which to alter is your decision. weight weenies shave down both cranks and chainrings all the time. i would probably hit the cranks since then you can change rings w/o problems, also removing material around bolt holes isn't always that good. i imagine the middle ring was steel and the material supporting the rings at the bolt holes was sufficient.
    file time flat bastard!

  12. #12
    domestique squeakywheel's Avatar
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    Looks like an aluminum chainring. That would be easy to file down.

    I bought a used steel 110 BCD chainring and found out it won't fit on my crank for the same reason. I'm planning to file it down a little. I'm expecting it to be a pain because I don't think the steel will be as easy to remove as your aluminum.

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