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  1. #1
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    Chainline vs. Shimano direction

    I'm building up a new frameset and rolling over my old stuff. Here's my problem/question -

    I'm using a Profile Racing crankset & I can mix-n-match spacers to get a "perfect" chainline. The problem is when I do that, the outer chainwheel sits way inside the F. derailuer cage. I've got the old "pro-alignment" block stuffed into the F. derailuer to line everything up & Shimano clearly says in their tech set-up directions, that everything's "right" up front when "The level section of the chain guide outer plate should be directly above & parallel to the largest chainring.". Now I admit I'm not really sure what they mean by the "level section", but from the pretty lil diagram, I assume they mean the vertical section ot the outer plate.

    OK, so I'm not a bike mechanic as you can tell, but it seems I can have one or the other here - so which one? If I set the chainring where Shimano wants it, my chainline falls a tick to the outside of the 6th cog. If I set the chainline right, the largest chainring is way inside the outer guide plate of the F. derailuer.

    So, if I go with the chainline - am I going to get shifting problems? Or if I follow Shimano's ideas am I going to get weird wear issues? Or...?

    The last set-up these parts were on was an 8spd. & I'm going to 9spd, but I don't recall this really being an issue then - but it's probably more likely that I'm paying alot more attention to the chainline now that I'm more comfy working on my own stuff.

  2. #2
    On MTBR hiatus :(
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    The included alignment block is probably set up for a 47.5mm chainline. The stated range of Shimano's front derailleurs is 47.5 to 50.0mm (from experience, their estimate is a touch conservative, but not by much).

    Ultimately, set the chainline up where you want it, but no further in than 47.0mm (as measured from the center of frame to the middle ring). Set the derailleur height with the recommended cage clearance over the big ring, even if that means manually exercising the derailleur (since using the block along won't reach).

    Set you low limit screw (a hair's clearance from rubbing the chain) prior to connecting the cable and making final adjustments.
    speedub.nate
    MTBR Hiatus UFN

  3. #3
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    Thanks - that's the kinda info I was looking for.

    I was worried that I wouldn't have enough low level adj if I went for the theoretically "right" chain line. As it turns out, following your info, I wouldn't have.

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