Eccentric BB Woes - Looking for answers!- Mtbr.com
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  1. #1
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    Eccentric BB Woes - Looking for answers!

    I bought my first single speed earlier this year, fell in love with the concept, and I've recently built my first SS from the frame up. The frame isn't single speed specific, so I'm using an eccentric bottom bracket and unfortunately I've run into a couple of problems with it. The main problem is that to get the chain tight enough, the EBB is moved as far forward as possible (3:00 position if looking from the drive side). I've only gotten a few rides in on the bike, but during each ride at some point the drive side cup slips downward to around the 5:00 position. I noticed after my ride today that each BB bearing is torched. This is after only 50 miles of riding, granted it was mostly in wet conditions. Could this have been caused by pedaling too long with the cups not aligned properly?

    Clearly I need to get to the root of the problem, but I'm in need of some advice. First off, I'm running a Sram XX1 crankset with a 32T direct mount narrow/wide ring and a 19T rear cog. As far as I know, there isn't any company producing a single speed direct mount ring, so I'm stuck using an even-toothed n/w ring. This leaves me unable to use a half link to shorten the chain to put the EBB in a different position. And of course taking out a full link leaves the chain too short for my current gearing. So if I'm seeing things correctly, I need to go with a new chainring/cog combo that will give me the same gearing ratio, but will tighten up the chain to where I can put the EBB in a more suitable spot so it is less prone to slipping. And this leaves me to wonder how to go about calculating what may work for me. Are there any easy answers? If not, I'd gladly settle for a complicated answer!

    Hopefully I've made everything clear. If I've left out any pertinent information, let me know and I'll clear it up as best as I can. Any help here is greatly appreciated!

  2. #2
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    Which eccentric are you using? Yes, the two sides sides need to be aligned or as you found out it takes out the bearings.
    "These things are very fancy commuter bikes or really bad dirt bikes, but they are not mountain bikes." - J. Mac

  3. #3
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    Quote Originally Posted by tiretracks View Post
    Which eccentric are you using? Yes, the two sides sides need to be aligned or as you found out it takes out the bearings.
    Thanks, yeah I figured that was the cause! Anyway, the BB is a Trickstuff Exzentriker (I think that's the proper spelling, at least). I'm not really educated on the names of the various types of EBB's, but it locks the spinning outer cups onto the inner cups using a bolted wedge-type system. The first time I had the cup slip was because it actually became slightly unthreaded from the BB shell, but I reassembled with the proper torque specs and the slippage has been with the outer cups since.

  4. #4
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    Use a torque wrench and get the specs right to stop the EBB from spinning in the frame. I had this problem as well. My EBB requires 6.75Nm on the screw that expands the EBB, which was a good bit more than I thought was needed when tightening by hand. I'm guessing there's a good chance yours will be different.

    As far as finding a similar gear ratio with different rings, use this chart and keep your current ratio: https://www.peterverdone.com/wiki/im...ear-ratios.gif

  5. #5
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    The term to solve your chain tension woes is "Magic Gear". Look for a calculator for this application: it allows you to figure out the same or similar gear ratio that provides a different chainstay length.

  6. #6
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    In an ideal world, you shouldn't have to worry about your EBB slipping no matter what position it is in. I used to have some issues with my EBB slipping until I started using Oatey's Pipe Compound in there (Niner SIR9 w/ Niner EBBII). They used to recommend using carbon paste or pipe compound in the Niner tech docs. Not sure why they don't anymore, but it solved my problem, so I'm still using it.

  7. #7
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    The Exzentriker is a particularly tricky EBB to get right.

    I had to use Carbogrip in the outer cups to get them to stay put

  8. #8
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    Quote Originally Posted by Acko View Post
    The Exzentriker is a particularly tricky EBB to get right.

    I had to use Carbogrip in the outer cups to get them to stay put
    Thanks for the recommendation, I've never seen a friction spray before. Seems like it could be a good choice! I did some careful measuring and calculating with some of the other links above and I've concluded that keeping the same chainring but moving to a 20T cog should give me the results I'm looking for. I'll report back when I get the new cog on! If the BB continues to slip, I'll try the friction spray.

  9. #9
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    this probably isn't the answer you want to hear, but you might also investigate a different tensioner.

    About three years ago I purchased a frame intending to set it up as a magic gear. That didn't work out, and I had to use a tensioner (I'm using a DMR STS). Initially I was completely bummed out to have a tensioner hanging off of the derailleur hanger... but damnn, that thing just works. It's quiet, reliable, and easy to set up. I love it. I've owned and EBB frame in the past, and would prefer this solution over an EBB.

    To each their own... but it's a thought.

  10. #10
    KgB
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    I am not familiar with you eccentric but I installed mine with grease and it hasn't slipped all season , as far as the chain, maybe try a worn chain or try a new chain, or a half link chain, but I am surprised you don't have enough adjustment for a halflink
    I've been inside too long.

  11. #11
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    Quote Originally Posted by KgB View Post
    I am surprised you don't have enough adjustment for a halflink
    OP can't use a half-link because he has a narrow/wide chainring.

  12. #12
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    30x18 is near identical in ratio...

  13. #13
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    Bottom line is that you don't get much adjustment with an eccentric adapter for a standard bottom bracket.

    Use this site to calculate a similar ratio with a shorter effective chainstay length.

    Other options include Phil Wood Philcentric (same method but different implementation...and I don't know if it will take a Sram crank), a White Industries Eric's Eccentric Eno hub or magic gear as mentioned above.
    I see hills.

    I want to climb them.

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