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  1. #1
    Senior Member robo's Avatar
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    Square taper BB and crank mystery... help!

    Ok, this is a strange one.

    I recently built up a new steel frame, with a Shimano UN-54 square taper BB and Sugino XD-600 cranks. The frame manufacturer recommended a 107mm BB, but i went with a 110mm at the recommendation of some other people who have this frame, because of the tight clearance.

    All parts and the frame were brand new.

    While installing the plastic removable sleeve of the BB, i used the wrong torque specification and broke the plastic, so i took it down to the LBS to see if they had any replacement sleeves. The mechanic there tried a whole bunch of sleeves until he found one that fit - it was an aluminum one too, which i figured was a good thing. He reinstalled the BB and the sleeve, cranked everything down, and i figured i was good to go. It looked like he was REALLY cranking it down too. I did ask him if the threads or BB shell needed chasing/facing, but he looked at me as if i had suggested he sacrifice a chicken over my bike, and shook his head. I only mention this in case it has relevance later on..

    I then took the bike home and installed the cranks myself, using a torque wrench and being conservative with the torque (using the lower end of the recommended torque). There was a good 2mm of clearance between the granny ring and the chainstay - tight, but OK.

    I rode about 25 miles, re-tightened the cranks (they had loosened just a little, as is normal, i think), and then didn't have time to ride until today, when i went on a longer ride. About 30 minutes in, i noticed that the cranks were wobbling - closer inspection revealed that the BB was totally loose. I made it back to the car, by which time, the cranks were wobbling at least 6-7mm laterally (at the ends of the crankarms) because of the loose BB.

    I got the bike home, took the cranks off, removed the BB, cleaned it off, scraped some paint off the drive side shell face with an XActo knife (the paint was cracking, presumably from the pressure of the BB's flange), and reinstalled the BB using Park Tool's recommended torques, about 400in/lbs on the fixed (drive) side and 360in/lbs on the sleeve side.

    Seemed fine, so i tried reinstalling the cranks.

    And here's the second weird thing. I installed the drive side crank again, to the same torque spec, and it went on so far that the granny ring got stuck against the chainstay, and actually gouged the paint pretty well before i realized what was happening.



    So my question is... what on earth?

    First of all, how did the BB practically fall out so quickly, and secondly, what happened to my chainline?

    Really strange, especially considering i'm using a BB thats 3mm longer than recommended and the parts are all new and 'normal' (ie. no wacky combinations AFAIK). The only possibly non-matching thing is the replacement sleeve, but i don't see how that would have an effect on the chainline like that.

    help!?!


    thanks,

    robin
    Last edited by robo; 04-25-07 at 06:34 PM.

  2. #2
    Gone, but not forgotten Sheldon Brown's Avatar
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    Any chance your frame has a 73 mm bottom bracket shell instead of the more normal 68 mm width?

    Some mountain bikes use 73 mm.

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  3. #3
    Senior Member robo's Avatar
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    Quote Originally Posted by Sheldon Brown
    Any chance your frame has a 73 mm bottom bracket shell instead of the more normal 68 mm width?

    Some mountain bikes use 73 mm.
    It's definitely 68mm - it's a Rivendell Bleriot and the specs say 68mm, and i double checked just now with calipers. 68mm for sure.

  4. #4
    Senior Member robo's Avatar
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    OK - this has been bugging the heck out of me.. I took both cranks off again, and measured the spindle. As i understand it, the two sides of the BB spindle should protrude the same amount from the BB shell, ignoring the width of the flange on the drive side. However, this spindle protrudes about 2mm less on the drive side than on the non-drive side. I took the measurements by (carefully) eyeballing it with a ruler, but i'm pretty sure i'm off by no more than +/- 0.5mm and there is indeed a difference.

    Is this normal? If not, is there a way to adjust it on a cartridge BB?

    Here's a diagram i made:

    Last edited by robo; 04-25-07 at 06:25 PM.

  5. #5
    hello roadfix's Avatar
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    There are asymmetrical BB's out there, yes...

  6. #6
    Senior Member robo's Avatar
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    But... is that normal? I'm really hoping this is a BB problem, not a crank (ouch) or frame (gasp!) problem, as either of those are much more expensive and/or involved to replace...

  7. #7
    MFA jjvw's Avatar
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    The BB stick out 2mm more on the non-drive side and you need more length on the drive? Can you flip it around?

  8. #8
    Senior Member robo's Avatar
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    OK.. looking for explanations here... I believe i installed the BB correctly (and even if not, the problem is somewhat baffling..)

    However, i did notice an inconsistency in the Park instructions.

    Basically, in their cartridge BB installation instructions, they say to 'snug' the flange side (drive side in this case), and then tighten the other (removable ring) side to 360 in/lbs. This seems to imply that the drive side is left relatively loose.

    Thread the cartridge body into bottom bracket by hand, being careful not to cross thread.

    Use BBT-22 or BBT-18 as appropriate to snug fixed flange against face of bottom bracket.

    Thread in removable ring to appropriate side.

    Secure removable ring to at least 360 inch pounds using torque wrench. If you are using hand wrench, and are holding the wrench 6 inches from axle, apply 60 pounds of pressure… which is tight. By securing removable ring, you are securing the other side at the same time. Removable ring pushes against fixed flange.
    On the other hand, on their suggested torque chart, they say to use 435-608 in/lbs for a Shimano Cartridge BB - presumably this means the BB itself (ie. the flange side)?

    Or did i misunderstand the instructions again and overtighten the flange side?

  9. #9
    Senior Member robo's Avatar
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    Quote Originally Posted by jjvw
    The BB stick out 2mm more on the non-drive side and you need more length on the drive? Can you flip it around?

    The two sides are reverse threaded (English threading) so i can't do that.

  10. #10
    me have long head tube TallRider's Avatar
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    It's worth noting that you didn't help yourself by using a 110mm bottom bracket instead of a 107mm. These two have exactly the same drive-side dimension; the 107mm is basically symmetrical and the 110mm has the non-drive-side spindle sticking out 3mm further.
    110mm is better for these cranks since it puts the pedals equal length from the frame's centerline (with the 107mm, the crank is in the same place, but the non-drive-side pedal is 2 or 3mm closer to the frame than the drive-side pedal).

    If it keeps coming loose, you can use threadlocker (e.g., loctite) to hold it in there.

  11. #11
    Senior Member robo's Avatar
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    Wait... really? Why is this not made clear anywhere else? How about, say, a 113mm BB. Is that also asymmetrical?

    BTW - further scrutinizing this setup, having taken the BB and cranks off again, it seems that the drive side crank seats itself further along the spindle than the non-drive side. I'm not 100% sure of this, but from just snugging one crank and then the other (not actually using the bolt) on the same spindle end, its seems that the drive side crank goes further on.

    Defective crank?

  12. #12
    hello roadfix's Avatar
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    Quote Originally Posted by robo
    I'm not 100% sure of this, but from just snugging one crank and then the other (not actually using the bolt) on the same spindle end, its seems that the drive side crank goes further on.

    Defective crank?
    I think that's just an illusion. I've seen that too.

  13. #13
    me have long head tube TallRider's Avatar
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    Yeah, it bugs me that no one talks about which cartridge square-taper BB's have symmetrical and which have asymmetrical spindles.
    You'd think Shimano would have a list of this or something.

    107 is symmetrical
    110 non-ds 3mm longer
    113 non-ds 2mm longer
    115 symmetrical or very close

    This is the case for Shimano BB's and for Nashbar copies, and everything I've seen in the sealed-cartridge-bb world that's designed to be Shimano-compatible.

  14. #14
    * vpiuva's Avatar
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    You just didn't have the cranks tightened down enough the first time around. I just did the same with a SS. Had plenty of clearance, crank loosened a little about the fourth ride. Retightened, and voila, interference.

    Your BB loosening - that's not one I've done outside of French DS.

  15. #15
    Senior Member TimJ's Avatar
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    Something here may be right but if I were you I'd call Rivendell. The main problem is the bb and crank combo they recommend isn't working clearance-wise and seemingly isn't going to work. I'm not saying call and blame them, just that I will bet they'll have the best advice for you.
    fun facts: Psychopaths have trouble understanding abstract concepts.
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  16. #16
    Senior Member robo's Avatar
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    Hmph... this is kind of starting to make sense. I just discovered this: http://www.sheldonbrown.com/bbsize.html#sugino

    AFAIK the XD500's listed there and the XD600's i have are the same cranks - the different numbers just refer to the type of chainrings they come with..

    And also here: Sugino XD600 - Ok with 9 speed chain? (timcupery - you say 113mm is symmetrical in this thread, BTW, just to nitpick )

    So anyhow.... it looks like maybe i should have used a 113mm BB in the first place.

    I guess i'll try to get one shipped overnight. Maybe this mystery is solved. Hopefully 2mm extra clearance will do the trick, which is what i'll get if timcupery's latest numbers are correct.


    Thanks all,

    Robin
    Last edited by robo; 04-25-07 at 08:48 PM.

  17. #17
    Senior Member robo's Avatar
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    Quote Originally Posted by TimJ
    Something here may be right but if I were you I'd call Rivendell. The main problem is the bb and crank combo they recommend isn't working clearance-wise and seemingly isn't going to work. I'm not saying call and blame them, just that I will bet they'll have the best advice for you.
    I think i'll try doing that tomorrow morning. However, from a bit of further reading, it seems that it's more the crank model than the frame that determines the proper BB length, and the cranks that Riv recommends are slightly different. Riv sells Sugino XD-2' s, and i used Sugino XD600s. They are very similar cranks, and people here and on the Bleriot list thought they were functionally identical, but it's plausible that they require slightly different BB spindle widths.

  18. #18
    me have long head tube TallRider's Avatar
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    Yeah, my cranks (on the Centurion) are XD2, and that's what I'm basing the 110mm recommendation on. The XD600 has different arm profile so it's clear taht they're forged in different mold than the XD2 so it's possible they take a longer BB spindle.

    Also, thanks for the tip - I edited my post from nearly a year ago where I'd said 113mm is symmetrical.

  19. #19
    Senior Member robo's Avatar
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    OK.. ordered a 68x113mm BB from Nashbar.. and ended up buying another $100 worth of crap

    They always get me

    Hopefully this will do the trick. I'll keep you guys posted.

  20. #20
    Since 1938... JunkYardBike's Avatar
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    If your new BB comes with a plastic ring, DO NOT torque it down to parktool specs. There have been several threads recently addressing this issue. I cracked one myself attempting to reach that torque. There is also speculation that torquing an aluminum NDS cup to that spec might compress the cartridge and cause problems.

    In my search for a compatible replacement adjustable cup, several LBS mechanics told me they simply snug both fixed and adjustable cups. Your problem may have been that while the adjustable cup on most of these cartridge BBs is simply a contact fit on the face of the cartridge, there is a flange that should fit snugly, but not tightly, around the casing. Maybe your replacement adjustable cup was too wide in diameter? One shop I visited recommended using plumber's tape to fill the gap.

    I probably have about 25 miles on my BB, which I tightened pretty well on the drive-side and just snugged on the NDS (though the cup this time is aluminum). Hasn't loosened yet.

  21. #21
    Senior Member robo's Avatar
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    ^^ I do know about the plastic cup thing, having been one of the people that broke theirs by following Park's instructions.

    As for the other stuff, i'm pretty sure now that the crank clearance and the way the BB was installed are not related. Right now i'm working on the assumption that my BB coming loose was a coincidence, rather than a problem related to the crank clearance. I guess with the new BB i'll just grease the threads well, torque the drive side down pretty hard, and torque the plastic NDS sleeve rather gently, and just keep an eye on it.

  22. #22
    Your mom
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    Yet another reason to throw away the torque wrench.

    I have heard that putting the NDS cup in first helps with installation as well.

  23. #23
    Senior Member robo's Avatar
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    Quote Originally Posted by tellyho
    Yet another reason to throw away the torque wrench.

    I have heard that putting the NDS cup in first helps with installation as well.
    Well, to be fair, it wasn't the torque wrenches' fault.. Although i agree in a way, in that if I hadn't been using a torque wrench, i would have been far more wary of putting so much torque into a flimsy plastic sleeve.

  24. #24
    Senior Member robo's Avatar
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    Here's an update, and hopefully mystery solved on both counts (bad clearance, and self loosening BB). Got the replacement 113mm BB on Saturday but didn't get around to installing until just now. It seems good. I torqued the drive side to about 400in/lbs and the plastic non-drive-side sleeve to about 120in/lbs. The crank clearance seems much better. After the initial installation, and about 360in/lbs of torque into the crank bolts, there is at least 3.5 mm of clearance between the ring and the chainstay lug. I expect this gap to close up after a bit of riding and a second tightening, but I think it should be enough space.

    The other discovery is what i think is an explanation for the other mystery, which was the BB that had worked itself loose after 25 miles or so. It turns out that the mechanic i took the bike to was a complete bozo. I didn't want to speak ill of him because he charged me so little ($16 for a headset install, spacers, a BB install, and finding a replacement NDS bb cup) but in retrospect, he screwed up on both tasks badly. The headset, he didn't install enough spacers and ended up cranking down the locknut against the top of the threaded steerer, rather than against the spacers and top cup. He did notice the fork clunking, but said it was 'because of the seals'. I had to go back to the shop for an extra 2mm spacer and redo it myself. And what i just discovered here was that the replacement NDS bottom bracket sleeve he put in was too wide on the inside, so that it was pushing against the BB body, but not holding it from flexing up and down on the ND side.. I suspect that it was this flexing that made the BB loosen up because of precession (because the flexing was coming from the opposite side from the threading, while the threading direction is chosen to prevent precession from flexing of the _same_ side, i believe). I'm just hoping riding on it this way didn't damage the BB shell threads.

    So yeah, be warned... this was Tread Bike Shop in Inwood (in Manhattan). I wouldn't normally name names but in this case they screwed up two out of two jobs, both of which could have resulted in damage to the frame and/or parts. The guy on the sales floor also told me my lugged steel frame was made of aluminum, which is just adding insult to injury.
    Last edited by robo; 04-30-07 at 11:58 AM.

  25. #25
    Your mom
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    This problem with BB cups has been discussed, but bears repeating in my opinion. LBS mechanics will tell you that all of Shimano's cartridge BBs have the same size cups. They don't. In fact, in canvassing to replace one I'd (stupidly) cracked, I got three different cups with, surprise, three different sizes. You have to match up the old and the new. Makes you wish for an old cup and spindle, huh?

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