how to adjust chainline w/ sq taper shimano un72 BB?- Mtbr.com
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  1. #1
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    how to adjust chainline w/ sq taper shimano un72 BB?

    I have a raceface turbine and a 107mm UN shimano bb. Chainline is all wrong and i need to bring the chainrings closer to the stays. The left arm is too close to the stays anyway so i have to move the right side only. Spindle is right for the BB. Is there any way to do it on those BB? I had a raceface before which was easy to do that but on shimano the cup is fixed in one side.
    I will take it to the lbs anyways since i donīt have the tools and stand but i want to know whatīs going to happen.
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  2. #2
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    In general, unless the BB is designed for this, (your’s isn’t, I believe), you get a new BB with the correct spindle length, or possibly just a new spindle if it’s really old school.
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  3. #3
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    Quote Originally Posted by rideit View Post
    In general, unless the BB is designed for this, (your’s isn’t, I believe), you get a new BB with the correct spindle length, or possibly just a new spindle if it’s really old school.
    Itīs the right length. And the left arm is too close to the stays anyways. I believe this crankset needs an adjustable BB... i may as well search for a shimano 737 xt crank instead of spending on a phil or any adjustable BB.
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  4. #4
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    buy the BB length for which the crankset was designed. that info could be hard to track down. I read a few references to using a 113mm spindle with that crankset.

    What's the actual current chainline on that crankset with the 107mm spindle? you can measure it thusly:

    (diameter of seat tube ➗ 2) + distance from drive side of seat tube to center chainring tooth tip.

    it should be 47.5 to 50 mm.

  5. #5
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    are you certain you have the correct width BB for the frame as well? they typically come in 68 and 73mm. using the wrong one would put the cranks off-center.

  6. #6
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    Quote Originally Posted by mack_turtle View Post
    are you certain you have the correct width BB for the frame as well? they typically come in 68 and 73mm. using the wrong one would put the cranks off-center.
    Itīs supposed to be 68mm and there is no bb cup hanging out the frame.
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  7. #7
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    Quote Originally Posted by mack_turtle View Post
    buy the BB length for which the crankset was designed. that info could be hard to track down. I read a few references to using a 113mm spindle with that crankset.

    What's the actual current chainline on that crankset with the 107mm spindle? you can measure it thusly:

    (diameter of seat tube ➗ 2) + distance from drive side of seat tube to center chainring tooth tip.

    it should be 47.5 to 50 mm.
    50mm.
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  8. #8
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    From what you're saying, it honestly sounds like the frame is either ****ed up, or built offset (like a Surly Pugsley).

    They din't get shorter than 107 in Shimano, so if it's too far away on the drive side, but too close on the non, somethings hinky in Denmark.
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  9. #9
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    If you're certain that the BB is the correct width and the spindle is the correct length, and the chainline is correct, then there's something wrong with your frame. Check your frame alignment in that case. the "string method" should be enough to tell if it's way off. most bike shops should have some sort of frame alignment gauge as well.

    https://www.sheldonbrown.com/frame-spacing.html skip down to "checking alignment."

  10. #10
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    Quote Originally Posted by MendonCycleSmith View Post
    From what you're saying, it honestly sounds like the frame is either ****ed up, or built offset (like a Surly Pugsley).

    They din't get shorter than 107 in Shimano, so if it's too far away on the drive side, but too close on the non, somethings hinky in Denmark.
    Rear wheels i have here all center fine on the frame. Itīs an Ibis steel mojo i bought new many moons ago. I have been working myself on the drivetrains and noticed a significant difference to my other frame.
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  11. #11
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    This is just a guess, but with the old Race Face BB - that is separate from the fixed and adjustable cups - it is possible to put it in either way around. I wonder if perhaps the 107mm is only possible when it's in "backwards" and if you should - when the fixed cup is attached to the BB - be looking at a longer spindle.

  12. #12
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    Quote Originally Posted by MendonCycleSmith View Post
    From what you're saying, it honestly sounds like the frame is either ****ed up, or built offset (like a Surly Pugsley).

    They din't get shorter than 107 in Shimano, so if it's too far away on the drive side, but too close on the non, somethings hinky in Denmark.
    In fact the bb shell is offset on the cstays by 0.5cm to the right. I donīt know if by design or mistake. Again.. itīs a 00 Ibis Mojo. It should be beyond perfect.
    When i measure chainline it reads 50mm so itīs within kosher lines. Itīs the first time i pay attention to those things: since covid i am wrenching on all my tools allow and i just went from rapidfire to thumbies. The throw on the left thumbie felt wrong so i i am trying to sort it out. I wish i had an uber luxe Phil BB so i could just place my chainline wherever i wanted.
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  13. #13
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    Quote Originally Posted by mainlyfats View Post
    This is just a guess, but with the old Race Face BB - that is separate from the fixed and adjustable cups - it is possible to put it in either way around. I wonder if perhaps the 107mm is only possible when it's in "backwards" and if you should - when the fixed cup is attached to the BB - be looking at a longer spindle.
    I would do a shorter spindle if there was one. I have enough clearance on left arm but too much on the right. The taperlock raceface BB would allow me to move the chainline but not shimano and there are no other bb than Phil to do it. I suspect this is an issue w/ the turbine crankset and they came w/ the bb to sort it out. The bb shell is offset by a couple mms to the right. Maybe 0.5cm. I could ride as it is but whatīs the fun in not obssessing w/ things on your bike?
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  14. #14
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    Quote Originally Posted by colker1 View Post
    Rear wheels i have here all center fine on the frame.
    I was not asking if the wheel is centered in the frame. I am asking if the frame is aligned. it can be one and not the other. it will take 60 seconds with a string and a ruler to check the frame alignment. it would be a good idea to confirm and rule that out.

  15. #15
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    UN72 bottom brackets do not have adjustable chainlines because the drive side cups are fixed.


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  16. #16
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    I'm kinda hands on with this sort of thing. Backseat diagnostic mechanicry never goes well for me....

    I have a couple Turbines on bikes, with Shimano BB's, nary a sweaty palm over set up and function.

    If you're saying it's a new frame, and alignment is spot on, I'd say measure your spindle and make sure it's correct.

    Beyond that, source a used Phil if new $ bugs you, as that'll solve the problem super fast and wonderfully!
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  17. #17
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    Quote Originally Posted by joeadnan View Post
    UN72 bottom brackets do not have adjustable chainlines because the drive side cups are fixed.


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    Well, you actually can space the drive side out a few millimeters, but obviously not in.
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  18. #18
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    Quote Originally Posted by rideit View Post
    Well, you actually can space the drive side out a few millimeters, but obviously not in.
    That did occur to me as I typed that, but decided not to overcomplicate the issue as OP already said that he had too much clearance on the right (drive) side. Spacing the DS out would exacerbate his problem.


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  19. #19
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    Quote Originally Posted by MendonCycleSmith View Post
    Beyond that, source a used Phil if new $ bugs you, as that'll solve the problem super fast and wonderfully!
    Or a vintage White Industries

    I also came across this idea to mod a Shimano https://veloapocalypse.wordpress.com...ottom-bracket/
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  20. #20
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    i measured and remeasured everything. Chainline seems to be kosher at 48mm. BB is welded offset but it may be a design plan w/ those swoopy chainstays. The right chainstays may be welded a bit more to the left to give more clearance. I have no other ibis mojo to compare.
    I have another bike, a fat cjty wicked, and the throw on the thumbshifter is different. No offset BB. Both front derr. seem to be set right and both chainlines read the same. Cranksets are different though: one has shimano m737 W/ the same 22 32 42 rings. I would like them to have the same thumbie throw when shifting.
    Yeah.. i may shell out for a Phil and play w/ it.
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  21. #21
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    Quote Originally Posted by mack_turtle View Post
    If you're certain that the BB is the correct width and the spindle is the correct length, and the chainline is correct, then there's something wrong with your frame. Check your frame alignment in that case. the "string method" should be enough to tell if it's way off. most bike shops should have some sort of frame alignment gauge as well.

    https://www.sheldonbrown.com/frame-spacing.html skip down to "checking alignment."

    It didnīt pass the string test. Misaligned by 3mm. Is that acceptable?
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  22. #22
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    I don't know what the margin for error for that string test should be. 2mm does not sound like much for such an imprecise test. it sounds like it's not obviously "bent" so I would try to find a shop with a proper alignment gauge to be certain how far off it is.

  23. #23
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    Quote Originally Posted by mack_turtle View Post
    I don't know what the margin for error for that string test should be. 2mm does not sound like much for such an imprecise test. it sounds like it's not obviously "bent" so I would try to find a shop with a proper alignment gauge to be certain how far off it is.
    3mm. I can see it without a ruler. A high end frame i bought new direct from Ibis. It was not cheap. It should not happen.
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  24. #24
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    now I am even more intriuged. let us know how Ibis responds.

    how old is "many moons ago"? has it been ridden all that time? sounds like it got tweaked over time from wear and tear or from a big impact. I had to look up that frame. it looks old.

  25. #25
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    Quote Originally Posted by mack_turtle View Post
    I don't know what the margin for error for that string test should be. 2mm does not sound like much for such an imprecise test. it sounds like it's not obviously "bent" so I would try to find a shop with a proper alignment gauge to be certain how far off it is.
    Itīs not imprecise since i tied the string same way on both drop outs. When the bike was built we had to seriously straighten the drop outs. It just leaves a bad taste in my mouth regarding Ibis.
    My fat chance is way better made than this and i am a third owner.
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  26. #26
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    Quote Originally Posted by mack_turtle View Post
    now I am even more intriuged. let us know how Ibis responds.

    how old is "many moons ago"? has it been ridden all that time? sounds like it got tweaked over time from wear and tear or from a big impact. I had to look up that frame. it looks old.
    Ibis wonīt respond. They are in the business of carbon made in china now. I bought the frame in 2000. Never crashed and i am a light user.
    Bottm bracket is seriously off set to the right. Seatstay bridge is slightly crooked and frame is misaligned. They did sold this frame as "bad paint" w/ a discount. I wonder what else was bad beneath the paint.
    I am into many different hobbies and bicycles is the only one that comes w/ so much screw ups. Mind you.. itīs never shimano and it always happens w/ high end frames. Thatīs not my first story.
    At least i rode this frame for 20 yrs even though it never felt as tight and balanced as my fat chance. The irony is tyhe fat was a used, non expensie buy and the Ibis was my dream bike.

    Itīs a 00 frame i bought new direct from Ibis.
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  27. #27
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    that frame is two decades old. I am glad to see things things hold up for a long time, but I think it's past its prime now. I am not a framebuilder, but I'd like to hear from one what they would expect in the lifetime of a steel hardtail like that. go ask in the framebuilders' forum.

    also, emailing companies like that is hit and miss for me. sometimes you get ignored. did you call them directly? (866) 424-7635

  28. #28
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    Quote Originally Posted by mack_turtle View Post
    that frame is two decades old. I am glad to see things things hold up for a long time, but I think it's past its prime now. I am not a framebuilder, but I'd like to hear from one what they would expect in the lifetime of a steel hardtail like that. go ask in the framebuilders' forum.

    also, emailing companies like that is hit and miss for me. sometimes you get ignored. did you call them directly? (866) 424-7635
    my other bikes are 30 yrs old and they are doing fine.
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  29. #29
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    At this point you can:
    A) whine about it some more. Boo-hoo.
    B) call Ibis and ask them for help, which is unlikely to bear fruit because it's 20 years old.
    C) fix it yourself. An old steel frame is not difficult to cold-set into alignment.

  30. #30
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    Quote Originally Posted by mack_turtle View Post
    At this point you can:
    A) whine about it some more. Boo-hoo.
    B) call Ibis and ask them for help, which is unlikely to bear fruit because it's 20 years old.
    C) fix it yourself. An old steel frame is not difficult to cold-set into alignment.
    Can I chose? I will whine about it some more. If you believe a 20 yr old steel frame is expected to misalign just because, for no reason, then i believe it will align itself if i whine about it. Ibis sure wonīt do 2 s%$&ts about it. I doubt anyone there had anything to do with this frame. They are doing carbon now.
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  31. #31
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    Quote Originally Posted by colker1 View Post
    Can I chose? I will whine about it some more. If you believe a 20 yr old steel frame is expected to misalign just because, for no reason, then i believe it will align itself if i whine about it. Ibis sure wonīt do 2 s%$&ts about it. I doubt anyone there had anything to do with this frame. They are doing carbon now.
    Just focusing on the solution for you: what was the original BB that you had on the bike? Presumably the UN72 that you want to install was not already on the bike.

    As long as the wheel is centred in the frame, a little asymmetry in the cranks would not be noticeable, in my estimation. If you get a slightly longer BB spindle with floating cups, you should be able to get an acceptable solution.

    I doubt if cold setting the frame would be a viable solution. We are talking about a BB and chainstay misalignment, not a dropout misalignment.


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  32. #32
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    Quote Originally Posted by joeadnan View Post
    Just focusing on the solution for you: what was the original BB that you had on the bike? Presumably the UN72 that you want to install was not already on the bike.

    As long as the wheel is centred in the frame, a little asymmetry in the cranks would not be noticeable, in my estimation. If you get a slightly longer BB spindle with floating cups, you should be able to get an acceptable solution.

    I doubt if cold setting the frame would be a viable solution. We are talking about a BB and chainstay misalignment, not a dropout misalignment.


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    I first built it w/ an m739 crankset and a Un72 68x110mm. Then it had xtr 950 which came w/ itīs BB and i donīt recall itīs length but we had to place a couple spacers to make it shift right. I never payed too much attention to chainline to tell you the truth. I just rode it in the middle ring.
    Currently has the race face w/ UN72 68x107 and untill i replaced the RFires w/ thumbshifters i didnīt care for what went on.
    Now that i measured and found the misalignment i am bothered: i always cherished the Ibis even when i never felt it gave me perfect balance. Almost sold the bike but i was so happy when i bought it so i kept it.
    If itīs doable i would like to align the frame but i donīt trust any shop in this town. I would have to do it myself.
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