XTR Crank arm comming lose- Mtbr.com
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  1. #1
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    XTR Crank arm comming lose

    Im not sure what the issue is but the arm keeps working lose on my crank. I had to replace it once because it messed up the splines. Its the arm oposite of the drive side. I dont have a tourque wrench to tightned it to spec so I just get it as tight as I can then I tighten the locking ring against the bottom bracket and tighten the small clamp bolt on it. I even put greeen loctitet on the spline this time but my last ride I could hear some creeking and sure enough I had to tighten it some more.

    So am I dooing something wrong or are these things just problematic?

  2. #2
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    mine gets 1/4 turn loose in a 6 hour ride...everytime
    i am afraid to locktite it and just tighten it when i clean my bike....

  3. #3
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    I haven't had a single problem with the tightness of the main bolt on my M975 cranks, and I've pulled my cranks apart many many times. I do have problems with the pre-load collar though...but that's beside your point though.

    Do the threads everywhere look good? Do you see anything wrong with the arm's splines this time around? Are you greasing the washer that's between the crank arm and the bolt (not sure if this is a problem, but I could see it being a potential)? That's all I can think to ask...but even if you answer, I still won't know the problem without playing with it.

    Good luck figuring this out.

  4. #4
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    *edit*
    which model it is makes a difference.
    Last edited by meltingfeather; 07-07-2011 at 06:45 AM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  5. #5
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    What model is it, M970?

  6. #6
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    Quote Originally Posted by ne_dan View Post
    What model is it, M970?
    Yes its the M970. I never put grease on the washer. I used green loctite. The green is for press fits not for threads.

    The locking collar screws on the arm before you put it on the BB . From what I understand you are supose to screw this all the way against the arm, then after you torque the arm down you turn the collar so it moves against the BB then you tighten the screw on the collar (the collar is split).

  7. #7
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    Quote Originally Posted by Niner nut View Post
    Yes its the M970. I never put grease on the washer. I used green loctite. The green is for press fits not for threads.

    The locking collar screws on the arm before you put it on the BB . From what I understand you are supose to screw this all the way against the arm, then after you torque the arm down you turn the collar so it moves against the BB then you tighten the screw on the collar (the collar is split).
    That's the preload adjuster thing, so you make sure its against the crank arm when you install the crank arm. Which it sounds like you are doing. Then like you said adjusting the preload and tightening that 2.5mm bolt.

    Are you greasing the interface between the spindle and the non-drive side crank arm. Also go to Harbour Frieght, Sears, or anywhere and get a torque wrench, its cheaper than replacing cranks. You should be torqueing the fixing arm bolt to 45-50nm or ft-lbs I can't remember which off the top of my head. Then you should check it to make sure it did not come loose after the first 50 miles.

    There really is no need anywhere for loctite, just grease the fixing bolt its aluminum, and the spindle and it should never come loose. Also make sure your BB is tight.

  8. #8
    Mtc
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    I've never had or seen one come loose.
    I will say that the torque spec it really high. If you use a torque wrench on it I;m willing to bet you'll see you haven't been tightening it enough. The Shimano tech described it as " So tight you may injure yourself". When I installed mine I'd use a long allen and tighten it till it felt like I was going to pull the tendons in my forearm. It almost like I'm working on my car suspension.
    All this is assuming your using the tension collar correctly.

  9. #9
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    Quote Originally Posted by ne_dan View Post
    That's the preload adjuster thing, so you make sure its against the crank arm when you install the crank arm. Which it sounds like you are doing. Then like you said adjusting the preload and tightening that 2.5mm bolt.

    Are you greasing the interface between the spindle and the non-drive side crank arm. Also go to Harbour Frieght, Sears, or anywhere and get a torque wrench, its cheaper than replacing cranks. You should be torqueing the fixing arm bolt to 45-50nm or ft-lbs I can't remember which off the top of my head. Then you should check it to make sure it did not come loose after the first 50 miles.

    There really is no need anywhere for loctite, just grease the fixing bolt its aluminum, and the spindle and it should never come loose. Also make sure your BB is tight.
    Thanks,good advice here. I will remove th eloctite and add grease. I have a tourqe wrench but I need a 3/8" drive one and I have 1/4" and 1/2" .I will get one this weekend.

  10. #10
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    Quote Originally Posted by Niner nut View Post
    Thanks,good advice here. I will remove th eloctite and add grease. I have a tourqe wrench but I need a 3/8" drive one and I have 1/4" and 1/2" .I will get one this weekend.
    You can get a 1/2 to 3/8 adapter for under 5 bucks

  11. #11
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    Quote Originally Posted by meltingfeather View Post
    *edit*
    which model it is makes a difference.
    The only Shimano crank with the BB pre-load collar is the M970.

    They changed back to the non drive side arm clamp on the new M980 (as it is a much better and simpler interface). So yeah...M970 is the only model it could have been.

  12. #12
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    I have the M960 cranks.

    I tighten the main crank bolt first, thus pushing the arm in towards the bb cups. I do this hand tight for the most part and then maybe an 1/8th of a turn at most to snug it down. Then I tighten the two 2.5mm bolts. I have never had mine come lose on me. No locktite ever used and always put a little grease on the splines and all bolt threads.

  13. #13
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    Quote Originally Posted by gearwhine View Post
    The only Shimano crank with the BB pre-load collar is the M970.

    They changed back to the non drive side arm clamp on the new M980 (as it is a much better and simpler interface). So yeah...M970 is the only model it could have been.
    hence the confusion about the preload collar in my first stab. it's the only model i'm not that familiar with. the installation instructions for that thing look like a freakin' circus!
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  14. #14
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    I have a bud who had a set of those...

    Quote Originally Posted by Mtc View Post
    I've never had or seen one come loose.
    I will say that the torque spec it really high. If you use a torque wrench on it I;m willing to bet you'll see you haven't been tightening it enough. The Shimano tech described it as " So tight you may injure yourself". When I installed mine I'd use a long allen and tighten it till it felt like I was going to pull the tendons in my forearm. It almost like I'm working on my car suspension.
    All this is assuming your using the tension collar correctly.
    And he had issues with them coming loose. I have no idea if or how he fixed it.

    But yeah, like others have said... invest in a torque wrench. For something as critical (and expensive if you mess it up) as a crankset, not using a torque wrench is like trying to see if your sick kid needs to go to the hospital for a fever by taking his temperature with your finger.

    Once you have the basic install done correctly for sure, then worry about if they are messed up.

    I had an M752 XT Octalink crankset for years. I know... totally different animal than the XTR M970s, but I think it's worth noting.

    From day one, they worked loose even though I installed them cleanly with a torque wrench tightened to spec. Yes, I actually RTFM. I finally had to resort to using Red Loctite on the crank arm bolt (between the bolt and the inside of the BB spindle, NOT in the spline area), and the problem went away. You use Red loctite on bigger bolts (>M8 size), Blue Loctite on smaller bolts. The crank arm bolts on those things are M12 size, IIRC.

    BTW, they were still pretty easy to get on and off with the self-extracting crank arm bolt.

  15. #15
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    You absolutely need a torque wrench for the M970 cranks. The amount of torque recommended for these cranks is really high and unless you are a super hero I don't think you can get them tight enough without the leverage of a long wrench. Also, the chance of screwing up something so expensive is too high without using proper torque.

    I found the M970 cranks to be stupid easy to install, and the lock ring to be no problem whatsoever. I think they are my favorite crank design that I have used due to ease of install and solid interface.
    IT'S NOT THE FALL THAT HURTS. IT'S WHEN YOU HIT THE GROUND.

  16. #16
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    Quote Originally Posted by 1SPD View Post
    I have the M960 cranks.

    I tighten the main crank bolt first, thus pushing the arm in towards the bb cups. I do this hand tight for the most part and then maybe an 1/8th of a turn at most to snug it down. Then I tighten the two 2.5mm bolts. I have never had mine come lose on me. No locktite ever used and always put a little grease on the splines and all bolt threads.
    huh?

  17. #17
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    I had a problem with mine where if you push on the cranks at 3 and 9 o'clock then flip the sides and push on them again they'd rock a little. I bought a new frame and the problem went away.

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