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Bottom bracket spindle lengthwise asymmetry

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Bottom bracket spindle lengthwise asymmetry

Old 09-30-18, 11:01 PM
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rseeker
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Bottom bracket spindle lengthwise asymmetry

My BB has a square taper spindle and caged 9-ball bearings. (Not a cartridge.) I've been inside my BB three times total, most recently two days ago. The first time I was in there I noticed the spindle cones are each at a different distance from the end. The DS cone is 35mm from the end; the NDS one is 37 or 38mm from the end.

Is this normal, or is this a flaw? And if it's normal, which side should the longer-distance end go on, DS or NDS? And why -- something to do with chainline?

When I got into this BB the first time, I noticed the longer end was on the NDS side, so that's where I've kept it. But now I'm starting to wonder if I reversed it or it was assembled wrong in the first place.

Why? Oh, no reason ...








Last edited by rseeker; 10-09-18 at 04:35 AM.
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Old 10-01-18, 12:08 AM
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Perfectly normal. DS is longer to accomodate the chainring(s).
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Old 10-01-18, 12:08 AM
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I THINK some cranks were made so that the DS crank put the pedal further out. So with a symmetric bb you got the pedals at different distance from the chainstays. The fix to this was an assymmetric bb with the long end on the NDS.
I might remember wrong. Other manufacturers might have done it differently.
Itís been some years. Had a bike that got different pedal clearance DS/NDS after receiving a modern bb. Might even be that I had to switch to a longer bb to get the arm to clear. This long ago, I remember the cursing clearer than the technical details.
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Old 10-01-18, 12:11 AM
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It's normal.
Various cranks needed different lengths for the DS. The 3-S is pretty common.

BTW you can remove the cages and fit 11 balls. The new grease will hold them in place.

Scroll down a bit and there's a chart of spindle lengths.
https://www.sheldonbrown.com/bbsize.html
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Old 10-01-18, 01:25 AM
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The right crank location is governed by where the chainline is. Quite close to the BB for a single speed/fixed gear/track bike. A step further out for double cranksets. Yet another for triple cranksets. Mountain bikes require further out so the crankset clears the chainstays. There are other factors that push the right crank further out. The point being that this is not up to the BB manufacturer but is governed by the type of bike, the gearing used, etc. Now the manufacturer does have a choice when it comes to the left, NDS crank. It can make the BB spindle symmetrical so both feet are the same distance apart or it can bring the left crank in, sometimes a lot, relative to the right crank to minimize the distance one's feet are apart. For most, the distance one's feet are apart is not an issue, but for some it is very important. There are riders for whom keeping the feet close together is far more important than how symmetrical the cranks are.

Two popular manufacturers take opposite approaches here. Every BB spindle I have seen from Sugino has been asymmetrical. Every Shimano BB spindle I have seen has been symmetrical. (My knees do far better with the asymmetrical and much narrower Sugino cranksets. The spindle you are looking at is from Sugino or a similar non-symmetrical BB. (If you don't like it, I'll take it off your hands.)

Edit: a reason the longer end on your bike is one the left, NDS could be that the former owner changed cranksets. There are at least two different taper standards for the spindle/crank interface. The tapers are very close but the sizing is quite different so the crank sits in a quite different place. It could be the second crankset sat two far outboard and made for a poor chainline so flipping the spindle meant the right crank now sat further in, improving the chainline. Left crank would to further outboard; odd but it won't hurt the bike at all. The previous owner might also have gone from a triple to a double or from a double to a single and done the same spindle flip to bring the right crank and cog(s) closer inboard.

Ben

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Old 10-01-18, 04:23 AM
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Could have done without the dirty pic... yuk
Longer side goes on drive side.
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Old 10-01-18, 05:23 AM
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Originally Posted by trailangel View Post
Could have done without the dirty pic... yuk
Longer side goes on drive side.
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Old 10-01-18, 05:26 AM
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Originally Posted by trailangel View Post
Could have done without the dirty pic... yuk
If that's a community standard I would edit it out. I'm reacting to the close-up a little myself, I can imagine some people being more sensitive.

The bike stays dirty and the paint stays distressed as a theft-resistance measure. If yuk is the reaction .. maybe it's working.

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Old 10-01-18, 05:31 AM
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Originally Posted by 79pmooney View Post
The right crank location is governed by where the chainline is .. etc.
Thanks for the detailed answer.

So I should work out the chainline geometry and Do The Math and it'll probably make sense then.

(If you don't like it, I'll take it off your hands.)
OK, noted. I'd be open to that if it ever comes to retiring that spindle.
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Old 10-01-18, 05:34 AM
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Originally Posted by Bill Kapaun View Post
BTW you can remove the cages and fit 11 balls. The new grease will hold them in place.

Scroll down a bit and there's a chart of spindle lengths.
https://www.sheldonbrown.com/bbsize.html
Great information, thank you.
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Old 10-01-18, 07:04 AM
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Originally Posted by trailangel View Post
Longer side goes on drive side.
Not always. I had an early '90's Trek 7000 mtb, purchased new, that had a square taper cup-and cone bottom bracket and a Shimano LX 110/74 triple crank. When I first overhauled it I found the spindle's longer end was to the non-drive side. I thought Trek had made an assembly mistake but when I reassembled it "properly" the nds crank arm hit the chainstay. In this case having the long end of the spindle to the nds was correct.
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