Tension, Tension, Tension- Mtbr.com
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  1. #1
    Team Awesome
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    Tension, Tension, Tension

    Blerg.

    I'm trying to convert my oh so slick custom steel 29er to a full time SS. When I started this project, I planned on using a Forward Components BB to tension everything.

    Here's my problem - My BB shell is 73mm wide, and my chainstays are too far out on the BB to let me mill it down 2.5mm per side and fit the BB cups in. THe BB cups will hit the chainstays.

    I've tried the half-link/magic gear, but I'm having a hard time with that. Plus, I don't want to be totally screwed if I break my chain in the middle of nowhere.

    I was planning on using a pair of XT 770 cranks for the build, and they would work if I could get the BB skinny enough. I would have to use 2 spacers on the drive side to get the granny gear bolts to clear.

    So the way I see it I have 2 solutions - Figure out the half-link, or grind off the granny gear bolts on the XT 770's.

    Has anybody tried this? Does anyone have a pair of XT/XTR cranks without granny gear bolt holes they can sell me?

    I'm kind of stuck. Thanks for your help.

  2. #2
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    Grinding off the granny gear bolt mounts is your ticket, and it's easy. Besides, it's an excuse to buy a Dremel and/or a 4" disc grinder and we're just going to pretend we didn't realize the implication that you don't have them, already.

  3. #3
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    Quote Originally Posted by EBasil
    Grinding off the granny gear bolt mounts is your ticket, and it's easy. Besides, it's an excuse to buy a Dremel and/or a 4" disc grinder
    Or a hacksaw and a file.....

  4. #4
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    Quote Originally Posted by Andy R
    Or a hacksaw and a file.....

    What, and stir your coffee with a fork?

  5. #5
    local trails rider
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    Everybody knows that shaping metal is totally impossible without power tools.

  6. #6
    local trails rider
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    But seriously: is tensioning the chain your problem, or is it the BB shell that is not the width you want?

    Are you totally opposed to having a chain tensioner on your bike, either in the dropout or at the BB, tensioning the chain next to the chainring?

  7. #7
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    Not sure I understand the whole problem, but how about an ENO eccentric hub?

  8. #8
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    I am opposed to having a tensioner on my bike. I don't want crap hanging off the rear end that I can break.

    Thanks for the info, looks like I will get all mad scientist on this thing.

  9. #9
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    Quote Originally Posted by mountainflow
    Not sure I understand the whole problem, but how about an ENO eccentric hub?
    + ONE
    Works great, And no crap hanging off of the rear end.

    Dropbar SS Mamasita
    XTC Composite 29
    CruX
    Anthem X 29
    Unknown trials bike

  10. #10
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    I like the ENO, but I have a pair of hope SS hubs already, so it isn't an option.

  11. #11
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    I got the original Forward Components eBB to work with a 73mm BB shell, but I had to trim the granny posts. The older eBBs were wider, so it only worked with cranks like the Shimano FC-M532, which had a spider that was hollowed out and cleared the the cups.

    The newer cups are thinner, but you'll still need to trim the granny posts.

  12. #12
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    Aarg--same problem

    Tried fitting my new Forward Components EBB/ Deore SS crankset to my EWR tonight--it hadn't even occurred to me to check the BB shell width (73mm, I now know) beforehand. The cups installed perfectly--maybe one mm clearance to the chainstay on either side--but now the left crankarm dust/adjusting cap won't even engage the threads on the spindle to permit tightening down the crankarm, even with all three spacers (two driveside, one non-drive) removed.

    Forward Components suggests you can face the bb shell down to 68mm, but the EWR's chainstays are too wide to permit that and still adequately tighten down the EBB cups.

    I'm pondering grinding off the granny bolts, which by eyeball will maybe move the driveside crank inboard another 3mm or so, but am still not sure if that'll be sufficient to get the crankset sufficiently snugged up.

  13. #13
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    Quote Originally Posted by da1edub
    I'm pondering grinding off the granny bolts, which by eyeball will maybe move the driveside crank inboard another 3mm or so, but am still not sure if that'll be sufficient to get the crankset sufficiently snugged up.
    If you are using the same Deore crank as I am (FC-M532), then it should work. For 73mm BB shells, you need one spacer, which needs to go on the non-drive side. The spider on the M532 crank will clear the cups with no spacers if you grind off the granny bolts. I have the old FC cups, which were deeper, and you had to pretty much grind the entire granny tab off. The newer cups are a bit shallower, so they should clear easier.

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