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Old 02-23-05, 07:10 PM   #1
dkvick
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XTR Bottom bracket bearings sucks

Does anyone know if you can buy aftermarket bearings to replace the crappy ones in a Shimano XTR outboard bottom bracket? The bottom bracket have started to act up already after one season of racing. I have seen that Race Face makes a bottom bracket that is compatible with the outboard XTR crank set.
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Old 02-23-05, 07:35 PM   #2
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You answered your own question.
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Old 02-23-05, 08:06 PM   #3
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Yes, as you said the RF ones will work. Thus far they seem to be holding up much better than the shimano bearings.
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Old 02-23-05, 09:21 PM   #4
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I thought that Shimano's outboard bearing cranks/bb's were the answer to the crappy bearings of ISIS?
I guess not.
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Old 02-24-05, 06:44 AM   #5
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That was not necessarily the intent. The idea was that spacing the bearings farther apart would stiffen the entire assembly up, in conjunction with the larger spindle that extends from the driveside crank. Larger bearings are also a good thing, but theory is nothing without proper execution.
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Old 02-24-05, 07:56 AM   #6
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That design is too much of a compromise. They put the bearings outboard not because they wanted to, but because there is no room for a large diameter tubular bb spindle in a standard BB shell. Those bearings are large diameter, but are shoved into such a tight space they use smaller diameter balls.
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Old 02-24-05, 08:11 AM   #7
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Originally Posted by darkmother
Those bearings are large diameter, but are shoved into such a tight space they use smaller diameter balls.
Smaller balls. ....A big gripe with octalink and ISIS in order to get a larger, stiffer spindle relative to square taper spindles and big balls. Is this really progress or marketing?

Last edited by sydney; 02-24-05 at 09:55 AM.
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Old 02-24-05, 09:51 AM   #8
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I don't think the spindle flexing is a problem for shimano, in and of itself. They wanted to redesign the crank/spindle interface. The square taper is a really poor design. Splined is a better idea, but I think they had problems with the first incarnation, and redesigned it with a deeper spline. On the XTR/DA stuff, using a large diameter steel tube means they can make the whole assembly way lighter. Ideally, they would redesign the bottom bracket shell at the same time, making it larger so the bearings could fit inside. I'll be curious to see how well these new BB's/cranks hold up over several years of use.
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Old 02-24-05, 10:00 AM   #9
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Originally Posted by darkmother
Splined is a better idea, but I think they had problems with the first incarnation, and redesigned it with a deeper spline.
Octalink V2 is longer and wider. And curiously was only used on MTB groups blow XTR. Go figger.
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Old 02-24-05, 10:08 AM   #10
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The square taper is a really poor design.
Really? By my count, it has worked fine for 50+ years....
I can buy a $25 UN-72 BB, and it will run fine and smooth, with no maintenance whatsoever for the next 3+ years. In salty Boston weather, too. There is NO other BB that can match that. Period.

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Old 02-24-05, 10:11 AM   #11
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Ideally, they would redesign the bottom bracket shell at the same time, making it larger so the bearings could fit inside.
Yea, then the rear spacing has to be increased to fit the newer chain line, and the Q factor is increased.
A whole can of worms, in my opinion.
Stick with square taper.
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Old 02-24-05, 10:16 AM   #12
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Originally Posted by BostonFixed
Yea, then the rear spacing has to be increased to fit the newer chain line, and the Q factor is increased.
A whole can of worms, in my opinion.
Stick with square taper.
In this case he meant wider BB shell to be bigger in diameter. It's already been done by FSA. Frame manufactrues probably won't buy it and it's just easier for component makers to go with outboard bearings and get gullible to buy into the hype.
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Old 02-24-05, 11:07 AM   #13
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Originally Posted by BostonFixed
Really? By my count, it has worked fine for 50+ years....
I can buy a $25 UN-72 BB, and it will run fine and smooth, with no maintenance whatsoever for the next 3+ years. In salty Boston weather, too. There is NO other BB that can match that. Period.
I use it on all my bikes too. It works, but it is not even close to a good solution to the problem. The joint is too unstable, and is not designed well for the forces involved. In order to get decent reliability, you have to run very high quality forged cranks. I suppose what I'm trying to say is there is a lot of room for improvement. Never the less, I've had the same set of square taper XTR cranks on my MTB for 12 years, and I have some on my commuter as well. Trouble free so far-not bad at all. For some reason, I've been toasting UN-72's once a season on my MTB. Fine for road though.

I will not invest in any new crank design until it has been around for a few years to ensure that replacement parts are available, and that it is reliable. With shimano bringing out a new design ever year, I'll probably use square taper for the rest of my life.
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Old 02-24-05, 12:00 PM   #14
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Originally Posted by darkmother
I use it on all my bikes too. It works, but it is not even close to a good solution to the problem. The joint is too unstable, and is not designed well for the forces involved. In order to get decent reliability, you have to run very high quality forged cranks.I suppose what I'm trying to say is there is a lot of room for improvement.
Really?
"The joint is too unstable" I'm not sure exactly what this means, but a properly installed square taper crank arm WILL NOT loosen. This mean using a torque wrench, etc. Checking the bolts is also a good idea periodically.
I don't own any high quality cranks, in fact an old set of shimano 105 cranks are my highest quality set. I wouldn't really call those high quality. I'm not sure what you mean by "decent reliability", but all of the cheap square taper cranks that i've used have worked great with no problems.
There is more flex with sqaure taper cranks, than with the splined systems, ISIS, etc. But the whole bicycle flexes. Handlebars, Stem, wheels, frame, etc.
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Old 02-24-05, 12:14 PM   #15
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Really?
"The joint is too unstable" I'm not sure exactly what this means, but a properly installed square taper crank arm WILL NOT loosen. This mean using a torque wrench, etc. Checking the bolts is also a good idea periodically.
I don't own any high quality cranks, in fact an old set of shimano 105 cranks are my highest quality set. I wouldn't really call those high quality. I'm not sure what you mean by "decent reliability", but all of the cheap square taper cranks that i've used have worked great with no problems.
No issues here either and that includes alot of less than top drawer stuff, in long term use. Personally prefer it to octalink and have no actual experience with isis.
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Old 02-24-05, 12:24 PM   #16
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I got 9 trouble-free years out of my Campy AC-S BB on my Bianchi. That includes quite a few good soakings on rides that turned rainy (3-day fundraiser that about every other year starts the day after a hurricane blows by Cape Cod). I've never noticed any flex in the BB or cranks.
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Old 02-24-05, 12:42 PM   #17
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One of the problems with the square taper, is the the crank squirms up the axle when riden. Try this: Install a crank, properly. Mark the position of the retaining bolt and ride for a few hundred miles. Check the torque again. What you will find is that the bolt is essentially loose, but has not turned relative to the spindle. The crank has moved up the taper. That is what I mean by unstable. If you continue to tighten the bolt after riding, you will chase the crank arm up the taper, and split the crank.

The nature of this design puts the crank arm in tension around the interface. This can lead to failures in low and high quality cranks. Additionally, the spindle itself has a very small cross sectional area, and can fail in fatigue, suddenly and without warning. If this happens on the left side of the bike, where it is more likely, then you have a reasonably good chance of falling in front of traffic. Installation is unpredicable, even with a torque wrench, as the friction between the crank and spindle depends on lubrication between the interface-dry fitting is especially unpredictable, but nearly everyone does it.

Just because something works adequately, doesn't mean it can not be improved. Drum brakes were standard on cars for a long time. They worked, but nearly as effectively as discs brakes do. I would not buy a car with 4 wheel drum brakes, given that disc technology is mature and far superior. I don't think splined cranks are the new "disc brakes" of the cycling world, but I do think there is potential for a superior design.
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Old 02-24-05, 12:45 PM   #18
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Originally Posted by darkmother
One of the problems with the square taper, is the the crank squirms up the axle when riden. Try this: Install a crank, properly. Mark the position of the retaining bolt and ride for a few hundred miles. Check the torque again. What you will find is that the bolt is essentially loose, but has not turned relative to the spindle. The crank has moved up the taper. That is what I mean by unstable. If you continue to tighten the bolt after riding, you will chase the crank arm up the taper, and split the crank.
You properly torque the crank, check it once after riding a bit.Then leave it alone. How many have split or had fail ? Or are you just regurgitating theory?
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Old 02-24-05, 12:56 PM   #19
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You properly torque the crank, check it once after riding a bit.Then leave it alone.
You can leave it alone if you're not concerned about it loosening up and ruining your crank arm (and even spindle, in extreme cases). We see that all too often at the shop. It's much more frequent with lower quality stuff, but the decent stuff is not immune to it if it is left unchecked for a prolonged period of time. It's not exactly difficult to check periodically and can save some money and aggravation in the long run.
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Old 02-24-05, 12:58 PM   #20
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I have had numerous cheaper cranks fail-more than I can count on my fingers. I have split cranks the way I described, before I knew better, and one after-a 90's shimano 105. That particular crank was installed with a torque wrench to spec, and never touched again. It split across the taper on the left crank while I was riding down a grass hill, 50/50 on the cranks.

I break stuff. Often. Lighter riders may not have the same experience. I've explained why I think the square taper is a less than optimal design, and also why I continue to use it.
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Old 02-24-05, 01:22 PM   #21
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You can leave it alone if you're not concerned about it loosening up and ruining your crank arm (and even spindle, in extreme cases). We see that all too often at the shop.
Never had one loosen up. Probably wasn't done right to start with.
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Old 02-24-05, 01:27 PM   #22
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Probably wasn't done right to start with.
I certainly hope you're not trying to intimate that the ones I worked on were done improperly. Anyone can properly prepare the bb/crank interface, read the torque specs, and install to same, particularly when you've done it literally hundreds of times.
Probably sounds a lot like guessing, anyways.

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Old 02-24-05, 05:41 PM   #23
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I certainly hope you're not trying to intimate that the ones I worked on were done improperly. Anyone can properly prepare the bb/crank interface, read the torque specs, and install to same, particularly when you've done it literally hundreds of times.
Probably sounds a lot like guessing, anyways.
Pay him no mind.
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Old 02-24-05, 05:50 PM   #24
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Im interested in FSA's megaexo. They say they have a bottom bracket which is ISIS interface, fully compatible with all ISIS cranks, yet uses the external bearings. I emailed their tech support about it because the only megaexo stuff i could find is with a whole new crankset. They said that they dont have any in stock and in a few months production will start again. Does anybody have information on this?
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Old 02-24-05, 07:00 PM   #25
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I have a set of Deore cranks that came on my 1987 Stumpy. They are square taper and have a little less than 25,000 miles on them. They have been on 6 bikes since I've had them. No cracks no signs of problems. The only problems I've ever had with square taper were loose bearing BB's. There may be issues with square taper cranks but I haven't once seen it on any of my bikes. I will always use square taper as long as I can get them.
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