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  1. #1
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    New question here. Bottom Bracket Replacement - Cross Reference?

    I need to replace my '04 Specialized Enduro Comp bottom bracket.

    The specs say that the OEM is a Shimano ES-30 68x121.

    My cranks are model FC-M540.

    I'm buyng a new cassette, chain, chainrings, etc. so I can freshen-up the bike when winter arrives. I ride frequently and the drive-train parts need replaced.

    Will any Shimano Octalink 68x121 bb fit? I'm having a hard time locating an ES-30 at the usually discount shops. I have found the bb, but for twice the price of an XT unit, which doesn't makes sense.

    My spider is also a little loose from banging the chainrings into rocks & logs, but just barely. I suppose I could replace the whole mess (cranks, bb, rings) but I'd rather just slap a new bb in it for now.

    Anyways, I see a ES-51 for $20 at Cambria bikes. Will that work?

    Thanks!!

  2. #2
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    The ES-30 was intended as an Original Equipment part available to manufacturers, and although you'll find them here and there, you ought to upgrade to the ES-51 of the same dimensions you located.

    You should also be able to use an ES-71 in a 68x118 size for this installation. This will bring your chainline in by 1.5mm, but you can easily stick a 1mm spacer under the drive side flange and not notice the difference.

    With the ES-71, you've got better seals and higher quality bearings for a smoother, linger life.
    speedub.nate
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  3. #3
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    Will I need the spacer on the #71?

    Shouldn't I be able to adjust my FD slighty to make-up the chainline difference. 1.5 mm seems pretty insignificant.

    Thanks for the answer.

  4. #4
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    Quote Originally Posted by weaklink
    Shouldn't I be able to adjust my FD slighty to make-up the chainline difference. 1.5 mm seems pretty insignificant.

    Thanks for the answer.
    Perhaps.

    Front derailleurs are designed around an "optimum" chainline of 47.5 to 50mm (distance as measured from the center of the frame to the center of the middle chainring).

    With your crankset and the 121mm spindle, that sets you right at 47.5mm. With the 118mm spindle, you'll be in at 46mm. Might not seem like much, but a lot of bikes have trouble dropping into granny, and that small inset of chainline could make the difference.

    No problem in checking it out and seeing if it works for you, but the bottom bracket spacers are cheap and it's easier to install one while you're changing the BB cartridge out.
    speedub.nate
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  5. #5
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    Spindle is not centered in housing.....

    Well, I'm screwed.

    I bought a 68-118 ES70 from Pricepoint. I also picked-up a 1.5 shim from my LBS, thinking that 121-118 = 3 difference. I figured the spindle would have been centered, so I only needed a 1.5mm BB spacer to keep my original chainline. I was wrong.

    The spindle is NOT centered. The new spindle is 4mm shorter on the drive side, which will not work on my bike. There's no way I'm going to try and shim the BB 4mm.

    I have a picture, but don't know how to insert in thread, and the upload image button at the bottom doesn't seem to be working....

  6. #6
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    I used a plastic vernier caliper, so the measurements are rough. But you get the idea...

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