Bottom Bracketry...
10-12-22, 07:24 PM
#1
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Bottom Bracketry...
To start off with, in my retirement I work at a bike shop. I volunteer full time at a bike collective. Not only that but I've been playing with and working on bikes of all origins and types for many years, I have a couple dozen bikes and I've disassembled them all among hundreds of others. I also have a very deep knowledge of all things mechanical. I like bikes in my later years because I just have a need to play with mechanical things, and they fit the bill as fun, healthwise, cheap and easy.
Soooo....
I am making another custom bike. I finished painting the frame and I go to screw in the new bottom bracket. I flip the frame over on the table and notice that the axle protrudes out one side of the bottom bracket more than the other. OK.... but its the non-drive side. the axle protrudes 3mm more to the left side of the bike than on the right. After staring at it a while I end up emailing the company that made the BB, mention the issue and start a return. I am assuming that the axle was installed in the bottom bracket backwards, with the offset on the wrong side. This, assuming there is supposed to be an offset.
Maybe I just have never noticed before and everything just worked out fine but I have always thought that there is a drive side offset to Bottom bracket axles of a few mm's to the drive side to accommodate the chain ring width(s). I have played with literally hundreds of Cottered cranks and every axle I've seen is offset to the drive side by a few mm's.
Here's the supposed kick...
On this build I am switching from a Cottered BB to A JIS tapered sealed cartridge. I've done this before at least dozen times and never had an issue. At least not one that I noticed. The BB company tells me that there is not supposed to be an offset on the drive side. But... I am sure that there has been a drive side offset in MANY of the sealed BBs I have installed in the past. Of course when replacing, one just measures the BB shell and axle length, goes to the shelf, gets a new one and installs and blah, blah, blah.
My first question to everyone here "in the know" is if they are aware of bikes that have anything but Bottom Bracket shells that are aligned other than straight down the center of the frame? Maybe I just haven't noticed it, but I thought all were placed in the center of the frame. I know there are a couple very early exceptions, but you are stuck re-fitting OG brackets on those.
What issue could possibly result in the axle on an otherwise perfectly aligned, spinning and working BB axle to be off to the left? This is not an adjustable thing. You screw in the left "cup" a ways, screw in the remaining entire cartridge all the way, tighten it, then screw in the left side till it seats and meets torque "spec."
Second is; Does JIS include not only the taper to attach the axle to the crank arm but also that the drive crank have more shallow receiver to compensate for the chain rings thickness?
I have been under the assumption that even the sealed cartridge units have a slight offset to the drive side to accommodate the width of the chain rings.
Like I mentioned, this is not the first time Ive switched from Cottered to JIS. but it is the first time Ive noticed a side to side difference. This may be the first time Ive gone from a two ring to a single and gauged the difference in the swap though. Im kinda sure the axle shouldn't protrude more to the left than the right in any case. That is the underlying issue.
The company alludes Ive installed the BB wrong but a 68mm shell is a 68mm shell and the standard threads are also. There isn't any side to side wiggle room to play with. The BB cartridge should fit it evenly at the very least, no matter the axle length it shouldn't be more to the left than the right....
Thoughts?
Soooo....
I am making another custom bike. I finished painting the frame and I go to screw in the new bottom bracket. I flip the frame over on the table and notice that the axle protrudes out one side of the bottom bracket more than the other. OK.... but its the non-drive side. the axle protrudes 3mm more to the left side of the bike than on the right. After staring at it a while I end up emailing the company that made the BB, mention the issue and start a return. I am assuming that the axle was installed in the bottom bracket backwards, with the offset on the wrong side. This, assuming there is supposed to be an offset.
Maybe I just have never noticed before and everything just worked out fine but I have always thought that there is a drive side offset to Bottom bracket axles of a few mm's to the drive side to accommodate the chain ring width(s). I have played with literally hundreds of Cottered cranks and every axle I've seen is offset to the drive side by a few mm's.
Here's the supposed kick...
On this build I am switching from a Cottered BB to A JIS tapered sealed cartridge. I've done this before at least dozen times and never had an issue. At least not one that I noticed. The BB company tells me that there is not supposed to be an offset on the drive side. But... I am sure that there has been a drive side offset in MANY of the sealed BBs I have installed in the past. Of course when replacing, one just measures the BB shell and axle length, goes to the shelf, gets a new one and installs and blah, blah, blah.
My first question to everyone here "in the know" is if they are aware of bikes that have anything but Bottom Bracket shells that are aligned other than straight down the center of the frame? Maybe I just haven't noticed it, but I thought all were placed in the center of the frame. I know there are a couple very early exceptions, but you are stuck re-fitting OG brackets on those.
What issue could possibly result in the axle on an otherwise perfectly aligned, spinning and working BB axle to be off to the left? This is not an adjustable thing. You screw in the left "cup" a ways, screw in the remaining entire cartridge all the way, tighten it, then screw in the left side till it seats and meets torque "spec."
Second is; Does JIS include not only the taper to attach the axle to the crank arm but also that the drive crank have more shallow receiver to compensate for the chain rings thickness?
I have been under the assumption that even the sealed cartridge units have a slight offset to the drive side to accommodate the width of the chain rings.
Like I mentioned, this is not the first time Ive switched from Cottered to JIS. but it is the first time Ive noticed a side to side difference. This may be the first time Ive gone from a two ring to a single and gauged the difference in the swap though. Im kinda sure the axle shouldn't protrude more to the left than the right in any case. That is the underlying issue.
The company alludes Ive installed the BB wrong but a 68mm shell is a 68mm shell and the standard threads are also. There isn't any side to side wiggle room to play with. The BB cartridge should fit it evenly at the very least, no matter the axle length it shouldn't be more to the left than the right....
Thoughts?
10-12-22, 07:36 PM
#2
Really Old Senior Member
I'm a bit ignorant on this because I've only dealt with 68mm shells.
Some "mountain" shells were 73mm.
I "believe" some replacement cartridges came with two 2.5mm spacers so you could use them on a 68mm shell.
If the NDS cup seemed to go in easier then normal, I'd surmise there may be something "going on" there.
Maybe somebody more knowledgeable can blow me out of the water
At least on the old spindle type, you knew what you did wrong and flipped the spindle in the correct orientation.
I owe a debt of gratitude to cottered cranks.
I had a 165mm double from a 1972ish 2x5 "road bike" that I was able to swap into my Rockhopper when I was experimenting with different crank lengths to alleviate knee pain.
They told me what I needed to know and I left them on until my new 165mm triple arrived. I did kind of like the klunky retro look.
Maybe you can post the actual brand/model/size of the BB you're installing? Maybe there's some known "quirk" about it?
Some "mountain" shells were 73mm.
I "believe" some replacement cartridges came with two 2.5mm spacers so you could use them on a 68mm shell.
If the NDS cup seemed to go in easier then normal, I'd surmise there may be something "going on" there.
Maybe somebody more knowledgeable can blow me out of the water
At least on the old spindle type, you knew what you did wrong and flipped the spindle in the correct orientation.
I owe a debt of gratitude to cottered cranks.
I had a 165mm double from a 1972ish 2x5 "road bike" that I was able to swap into my Rockhopper when I was experimenting with different crank lengths to alleviate knee pain.
They told me what I needed to know and I left them on until my new 165mm triple arrived. I did kind of like the klunky retro look.
Maybe you can post the actual brand/model/size of the BB you're installing? Maybe there's some known "quirk" about it?
Last edited by Bill Kapaun; 10-12-22 at 07:47 PM.
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10-13-22, 04:00 AM
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Some companies make "universal" bottom brackets that will work with 68mm and 73mm bottom bracket shells. They are actually 73mm bottom brackets, but they come with a 2.5mm spacer that goes on the drive side and makes them evenly spaced in a 68mm shell. You don't say what bottom bracket you have, but it is likely the case here.
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10-13-22, 06:25 AM
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Some companies make "universal" bottom brackets that will work with 68mm and 73mm bottom bracket shells. They are actually 73mm bottom brackets, but they come with a 2.5mm spacer that goes on the drive side and makes them evenly spaced in a 68mm shell. You don't say what bottom bracket you have, but it is likely the case here.
It's an Omniracer, it came with no shims or spacers and is clearly marked 68x118. Fitting it in a 71' Dawes, American spec 531 Galaxy frame.
We sell two Generic brands and Shimano at the shop. But my challenge is to turn this old frame into a 20lb "path racer / gravel bike," so I typed "lightweight BB" into ebay's search bar and omniracer is what popped up.
It is half the weight or less of the same MSW BB on the shelf. Looks pretty much the same besides the materials it's made from.
I swapped out a customers 3 piece cup and ball set with an MSW cartridge just last week and had no issue. It's axle was JIS so it all bolted back together and was fine like others I've done before.
This one started out a cottered setup but all is being switched to JIS of course.
Last edited by macstuff; 10-13-22 at 06:49 AM.
10-13-22, 09:17 AM
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I'm going in to the shop today so I'm going to measure several of each kind and remove a few arms on cartridge BB bikes to measure side to side differences.
I've already checked my cottered and JIS 3 piece cup and ball axles here at home and they all have a left/right difference.
I'll get to the bottom of this...
I've already checked my cottered and JIS 3 piece cup and ball axles here at home and they all have a left/right difference.
I'll get to the bottom of this...
10-13-22, 02:54 PM
#6
Senior Member
The attached shows specs that are commonly found on many BB. This is from Tange, and it seems that Shimanos are very similar.
For most 68/73mm BB, the right is longer, to varying degrees. Note that the 111mm has a longer NDS than the DS.
As for your question of BB shell alignment to the frame, some are slightly offset from the centerline of the frame. This is usually by just a small amount. Cannondale that I've seen sometimes are offset to the DS by a mm or so. I haven't seen/worked on too many vintage bikes, so can't comment on those.
For most 68/73mm BB, the right is longer, to varying degrees. Note that the 111mm has a longer NDS than the DS.
As for your question of BB shell alignment to the frame, some are slightly offset from the centerline of the frame. This is usually by just a small amount. Cannondale that I've seen sometimes are offset to the DS by a mm or so. I haven't seen/worked on too many vintage bikes, so can't comment on those.
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10-13-22, 03:36 PM
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Some companies make "universal" bottom brackets that will work with 68mm and 73mm bottom bracket shells. They are actually 73mm bottom brackets, but they come with a 2.5mm spacer that goes on the drive side and makes them evenly spaced in a 68mm shell. You don't say what bottom bracket you have, but it is likely the case here.
