Upgrades performed, need more advice- Mtbr.com
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  1. #1
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    Upgrades performed, need more advice

    I just upgraded/replaced my crankset,chain and cassette with some new low cost replacement pieces. Now when I try to change gears on the crank, it stays on the smallest chainring. The derailluer is adjusted properly, but I think the spacing on the new crank is very different from the old set.

    The new crankset is the Shimano M340. Not sure of the old one. I still have the original bottom bracket on the bike and its measurements are 68/122. I'm thinking I need to go to a 68/110 due to my measurements taken from the outer chainring to the inner part of the front derailluer is 14mm.

    What do you guys think???

  2. #2
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    Your BB width is determined by your cranks. You'll need a 123mm square taper BB provided your cranks are bored for square taper. 126mm for Octalink cranks.

  3. #3
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    The 123mm is OEM. I think I need something shorter due to the different offset of the new crank

  4. #4
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    123mm is the width given by the Shimano product manual for M340 cranks. Your BB spindle width is not determined by your frame; it is determined by your cranks.

    More than likely if your chain isn't shifting past the small ring, it's your FD adjustment and not your BB width.

  5. #5
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    OK, I'm gonna dig deeper into adjusting the FD. Thanks.
    Last edited by frdfandc; 09-19-2007 at 07:55 PM.

  6. #6
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    It really sounds like your limit screws aren't adjusted correctly.

    You never did specify whether you have an Octalink or square taper BB/cranks. If you are running Octalink, make sure your splines are lined up. If they aren't, the drive side crank will not sit down on the spindle where it's supposed to, forcing your crankset to be too far outboard of your BB shell which could possibly cause your FD not not shift properly.

    Our bikes are designed to have a 50mm chainline. With the M340 crank and the correct size BB width I gave you as specified by Shimano, you'll actually have a 51mm chainline. That's OK, 1mm isn't going to kill your performance. Although I'd recommend replacing your BB as well, you should be OK with the 122mm provided its in good condition.

  7. #7
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    Its the square taper BB and its still in good condition. I believe its still the original unit, but it doesn't make any noise and the bearings still look good. I'm only replacing things that are absolutely needed right now so I can get back riding and until I purchase my new ride.

    I started look closer at the FD and you are correct as the limiting screws need to be re-adjusted out.

    Thanks

  8. #8
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    Well, I spent almost 2 hours messing around with the FD. I cannot get it out far enough to get it onto the big chainring. So I remeasured and I found out I need to replace the BB. So off to the Performance store I go.

    Thanks again.

  9. #9
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    I ended up getting a 113mm BB, made the proper adjustments to the FD and now it works perfectly.

    Once I get a few miles on the new setup (after new cassette install) I'll readjust everything and off I go.

    Thanks for the help.

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