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  1. #1
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    Chain tensioner 73mm bottom bracket external bearing, no ISCG. What works?

    What chain tensioner will work and how, with a 73mm bottom bracket shell, external bearings, no ISCG tabs. I picked up a second-hand Blackspire Stinger, but when attempting to use it, when mounting it behind the BB cup, it acts as a "spacer" and therefore the non-drive side crankarm hits the BB and binds/cannot turn/etc.

  2. #2
    GUIDANCE COUNSELOR
    Reputation: NoahColorado's Avatar
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    Are you looking for a single or dual ring guide?

    What kind of crank and BB do you have?

    Have you physically measured your BB width?

    Cheers
    NOAH SEARS
    MRP
    TECH QUESTIONS HERE: INFO@MRPBIKE.COM

  3. #3
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    Dual ring. Crank is Truvativ Stylo Team GXP, bottom bracket that goes along with it. Bike is 2010.5 Turner 5 Spot, bottom bracket shell is 73mm. Thanks for any help

  4. #4
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    Reputation: Fix the Spade's Avatar
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    That is an excellent question. For bb mount parts you might struggle, I can't think of any that don't act as a spacer and alter the chain line.

    I was going to suggest one of these: http://bionicon.com/parts/c-guide.html

    It mounts on the chainstay and they work great... except on a 5Spot where the stay is way up in the sky.

    You could try making a similar device with a longer arm to reach the chain, but other than that I'm stumped!

  5. #5
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    The GXP threaded BB should be able to accomodate the chainguide "spacer" thickness as long as it isn't mucher thicker than 2.5mm because the non-drive side bearing is what the crank arm/spindle is tightened against and the drive side cup/bearing is able to float to accomodate the guide. No additional spacers should be used.

    NoahColorado gives a good description of it here: XX Cranks and Chainguide Fit Issue

    Quote from this thread below:



    -------------------------------------------------------------------------
    "No problem.

    First of all, understanding the GXP system helps.

    GXP works differently than Shimano, Raceface, FSA, or other similar external BB systems. Whereas those systems feature a spindle with a consistent 24mm OD, on GXP cranks the spindle steps-down slightly on the end. So essentially the ID of the non-driveside BB is smaller than that of the driveside. Thus, the spindle bottoms out on the inside of the non-drive side BB cups bearing. Therefore, spacers on the drive-side have ZERO effect on chainline (unless you have wayyyy to many spacers TOTAL and the spindle no longer bottoms out on the non-drive side BB cup).

    On a Shimano/Raceface/FSA style crank, installing a BB mount guide means REPLACING a BB spacer with the guide's backplate.

    On a SRAM/Truvativ GXP crank, installing a BB mount guide means ADDING the guide's backplate between drive-side cup and either the 1)BB shell (73mm) or 2) single spacer (found on a 68mm setup)

    Example of GXP 68/73mm cranks with various setups:
    68mm shell, no non-drive side spacers = chainline 2.5mm further outboard than standard
    68mm shell, 1 non-drive side spacer = normal chainline
    68mm shell, 2 non-drive side spacers = chainline 2.5mm further inboard than standard
    73mm shell, no non-drive side spacers = normal chainline
    73mm shell, 1 non-drive side spacer = chainline 2.5mm further inboard than standard

    maximum allowable "parts width" on 68/73mm GXP cranks is 75.5mm - no combination of spacers, bb shell width, guide, e-type derailleur, etc can exceed this or the crank will NOT bottom out on the non-drive side BB cup (you'll get binding, play, all kinds of problems).


    So, why doesn't SRAM/Truvativ call for a spacer on the drive-side of 73mm shells? It doesn't need one - makes no difference to the crank. But that doesn't mean you couldn't put one there (or install a e-type derailleur or BB mount guide) if you wanted to.

    Also, there really is no "preloading" the bearings on GXP system like on Shimano/Raceface/FSA system - you either have it tightened down all the way or not. There is virtually no way of crushing the non-drive side bearing. Think of it this way: on a Shimano/Raceface/FSA setup, tightening down the fixing bolt is essentially pinching the whole crankset together (no "hard" stop), with GXP you're just pinching between the spindle "step" and the left crank arm (a fixed distance with a hard stop).

    So yes, BB mount Lopes guide on 73mm shell is no problem.

    *The only combo that doesn't work, as far as I know, would be trying to setup a Truvativ X-guide on a CONVERTED triple crank (a standard triple crank with the "big" ring removed). The MRP 2x works for this, but the X-guide only designed to work with 2x10 cranks.
    NOAH SEARS
    MRP
    WHITE BROTHERS
    TECH QUESTIONS HERE: INFO@MRPBIKE.COM"

  6. #6
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    Quote Originally Posted by Fix the Spade View Post
    That is an excellent question. For bb mount parts you might struggle, I can't think of any that don't act as a spacer and alter the chain line.

    I was going to suggest one of these: http://bionicon.com/parts/c-guide.html

    It mounts on the chainstay and they work great... except on a 5Spot where the stay is way up in the sky.

    You could try making a similar device with a longer arm to reach the chain, but other than that I'm stumped!
    Great suggestion, I have been using bionicon's parts for years now and I am totally happy with them so far...

  7. #7
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    Ok so if Im understanding, it wont work because I do have a triple crank that Ive setup as double with bashguard?

  8. #8
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    I had this problem before on my old 575 with stylo cranks. Ended up buying an SLX double with bash crankset so that I could use a stinger since the truvativ cranks won't allow it. If you want to run a double guide, I'm almost positive you need new cranks, or have to use one of the bionicon c guides that mount to the chainstay.
    2013 Medium Santa Cruz Blur Trc in Matte/Silver, full XT kit, 1x10 with 32T wolftooth ring, 25 pounds 7 ounces

  9. #9
    GAME ON!
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    don't need a tensioner. just use a e13 xcx st. i have a similar setup. no problems.
    RIP Adam Yauch

    "M.C. for what I AM and do, the A is for Adam and the lyrics; true"

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