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Thread: Newbie Question

  1. #1
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    Newbie Question

    What's the differences in these bottom brackets, other than their intended uses but why do some of those have those cups on the outside and some don't? Which type is recommended if there is a preferrence?




  2. #2
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    the ones with the cups on the outside are external BB
    the other is an isis I believe, there is also a square taper
    the external type are supposed to be stiffer because the bearings are spaced farther apart on the axle.
    In my opinion, the internal type are better because there is less friction from the seals and having the bearings inside the bracket protects it from dirt and water better

  3. #3
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    Oh I see, are square tapers good too?

  4. #4
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    Quote Originally Posted by kryogenix
    Oh I see, are square tapers good too?
    some are but they are getting rare, mostly what you see are cheap $20-$30 shimano
    the square taper type have mostly been replaced by isis & external Phil Wood still makes a good one

  5. #5
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    I think my current crankset uses a some Shimano square tapered bottom brackets and I plan on replacing my bottom bracket because my Shimano one cracked and I don't know how? And so, if I buy a new bottom bracket that's an ISIS, that would mean I'd have to look into a new crankset too?

  6. #6
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    Quote Originally Posted by kryogenix
    I think my current crankset uses a some Shimano square tapered bottom brackets and I plan on replacing my bottom bracket because my Shimano one cracked and I don't know how? And so, if I buy a new bottom bracket that's an ISIS, that would mean I'd have to look into a new crankset too?
    thats right, you can replace the BB easily or the shop can, 20min job
    you can get a shimano sq taper for pretty cheap, the phil woods is $120
    go to the park tools web site , the have detailed instructions . you will need a couple of specialty tools

    if you do it yourself, when you put it together, clean the inside of the square hole on the cranks with degreaser, attach it to the square axle, grease the threads on the attaching bolt and torque it down hard 300 in lbs + do not grease the axle or taper hole. if after riding you notice the arms coming loose, immeadiatly retighten, dont keep riding, the square hole and axle will round over and will never stay on
    Last edited by dan0; 11-04-2007 at 05:17 PM.

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    Quote Originally Posted by kryogenix
    I think my current crankset uses a some Shimano square tapered bottom brackets and I plan on replacing my bottom bracket because my Shimano one cracked and I don't know how? And so, if I buy a new bottom bracket that's an ISIS, that would mean I'd have to look into a new crankset too?
    Read the reviews and search this forum before purchasing a new ISIS BB and crankset. Many of us have not had the best of luck with them. That said, the ISIS BBs made by SKF look pretty good. They use roller bearings instead of ball bearings and supposedly have better seals. They're kind of expensive, but if they hold up, they're worth it.

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    Quote Originally Posted by dan0
    the external type are supposed to be stiffer because the bearings are spaced farther apart on the axle.
    The external type is also supposed to have larger bearing balls than an ISIS or Shimano Octalink BB. Larger bearings stand a better chance of lasting longer, provided of course that dirt and other contaminants are kept out.

    The problem that I have with most external bearing cranksets is that they tend to move the chainline out more than an ISIS or square taper BB. When using an external bearing crankset, you're usually forced to use a 50mm chainline unless you play games with the spacers. In spite of this problem, I'm currently using external bearing cranksets on two of my bikes.

  9. #9
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    Quote Originally Posted by dan0
    torque it down hard 300 ft lbs
    Major error here! A torque like that would be for a bolt aboit 1.5" in diameter.

    do not grease the axle or taper hole. if after riding you notice the arms coming loose, immeadiatly retighten
    Many people, especially mechanical engineer Jobst Brandt, don't agree with you.
    Last edited by Mike T.; 11-04-2007 at 06:59 PM.
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    torque it down hard 300 ft lbs + do not grease the axle or taper hole
    Yes, major error!!! 300 ft-lbs would certainly strip the treads inside the BB, anything near that will plasticly deform the bolt, the axle and the crank. For reference, always follow manufacturers instructions, but to give some frame of reference 70 ft-lbs holds a cylinder head on an engine, and 60 ft-lbs holds the wheels on your car.

    For the years from 1990 - about 2002 when I was using square taper BBs, I lightly greased the taper, then applied 35 ft-lbs or so tourque to the bolt. Never a failure. A few times things got squeaky - just pull off the crank arm and clean things up, a little new grease then you are good as new.

    Better yet - go to your LBS nd let a mechanic show you what to do. That is what he is there for.

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    Quote Originally Posted by lunk57
    Yes, major error!!! 300 ft-lbs would certainly strip the treads inside the BB, anything near that will plasticly deform the bolt, the axle and the crank. For reference, always follow manufacturers instructions, but to give some frame of reference 70 ft-lbs holds a cylinder head on an engine, and 60 ft-lbs holds the wheels on your car.

    For the years from 1990 - about 2002 when I was using square taper BBs, I lightly greased the taper, then applied 35 ft-lbs or so tourque to the bolt. Never a failure. A few times things got squeaky - just pull off the crank arm and clean things up, a little new grease then you are good as new.

    Better yet - go to your LBS nd let a mechanic show you what to do. That is what he is there for.
    my misstake, should be inch pounds

  12. #12
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    Quote Originally Posted by lunk57
    Better yet - go to your LBS nd let a mechanic show you what to do. That is what he is there for.
    Seeing as you posted this in response to my post, my reaction is "You gotta be freakin' kidding me!"

    Pose the question "Grease square axle tapers or not?" and I'll bet every penny I own that plus or minus about three percentage points 50% of them will give the wrong answer.
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  13. #13
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    Quote Originally Posted by Mike T.
    Seeing as you posted this in response to my post, my reaction is "You gotta be freakin' kidding me!"

    Pose the question "Grease square axle tapers or not?" and I'll bet every penny I own that plus or minus about three percentage points 50% of them will give the wrong answer.
    I understand what he's saying, but I have 2 questions. even though the greased spindle will allow for greater accuracy in torque settings, isnt welding the spindle to the crank arm more important? most of us have had occasions where we forgot to grease the threads on the pedals or cleat bolts, what happened? allmost impossibl;e to remove. by greasing the bolt threads and not the taper itself you get the best of both arguments, the greased bolt helps with the torque, and the ungreased taper fuses with the crankarm
    and secondly, dont most manufacturers recommend dry installation?

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    Pose the question "Grease square axle tapers or not?"
    Actually I got this info from a LBS mechanic that I trust. I guess the "trust" part comes into play here, just like anything there are good ones and bad ones. Then I grew up went to engineering school and the grease thing made sense to me:

    Dan0, I don't think we are looing for fusing metal here, It is the geometry between the taper on the crank and on the axle that creates the lock, not the friction of the metal to metal contact. I have a park crank remover and it is very difficult to remove a crank arm even with grease in place. I would tend to think that if there were some gauling (welding) of the crank arm, this would be a one time deal - if you remove material from the crank, that geometry is lost between the tapers for the next time it is installed. And it is always the crank that would loose material - soft aluminum vs. hard steel or Ti.

    I don't have the answer about what the manufacturers reccommend - any bike shop or otherwise knowledgable people out there?

  15. #15
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    Quote Originally Posted by lunk57
    Actually I got this info from a LBS mechanic that I trust. I guess the "trust" part comes into play here, just like anything there are good ones and bad ones. Then I grew up went to engineering school and the grease thing made sense to me:

    Dan0, I don't think we are looing for fusing metal here, It is the geometry between the taper on the crank and on the axle that creates the lock, not the friction of the metal to metal contact. I have a park crank remover and it is very difficult to remove a crank arm even with grease in place. I would tend to think that if there were some gauling (welding) of the crank arm, this would be a one time deal - if you remove material from the crank, that geometry is lost between the tapers for the next time it is installed. And it is always the crank that would loose material - soft aluminum vs. hard steel or Ti.

    I don't have the answer about what the manufacturers reccommend - any bike shop or otherwise knowledgable people out there?
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