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Discussion Starter · #1 ·
To the mechanics--I'm installing a plain Jane Shimano cartridge, English square-taper bottom bracket. There's a little gap on the driveside. The bb will thread in all the way and snug up to the shell but not with the nondriveside (nylon/plastic) cup tightened. Is it possible the nondriveside cup is too wide (not leaving enough room for the bb to thread in all the way)? Is a slight gap okay on the driveside or is that inviting trouble? Thanks for any help.
 

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Could one of the cups be hitting the screw holding the bottom bracket cable guide? Most are held on by a screw that goes into the BB shell. Are you using the correct size bottom bracket? Some shells are 68mm wide, some 70mm wide.
 

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Discussion Starter · #8 ·
wim said:
Ah, that's it.
Yeah, the fixed side will thread in all the way but then the plastic side sticks out pretty far. So I loosened the fixed side, threaded in the plastic side a little further and then tried to tighten the fixed side--but now it won't thread in all the way.

From what I've been learning I wonder if the plastic cup is for a 73mm bb instead of 68.

Ryan
 

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rcnute said:
Yeah, the fixed side will thread in all the way but then the plastic side sticks out pretty far. So I loosened the fixed side, threaded in the plastic side a little further and then tried to tighten the fixed side--but now it won't thread in all the way.

From what I've been learning I wonder if the plastic cup is for a 73mm bb instead of 68.

Ryan
Depending on what you mean by "sticks out pretty far," it may not be a problem at all. I've got a bike on which the plastic side's been sticking out about 3 mm for years now, with the BB still working just fine.
 

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rcnute said:
Yeah, the fixed side will thread in all the way but then the plastic side sticks out pretty far. So I loosened the fixed side, threaded in the plastic side a little further and then tried to tighten the fixed side--but now it won't thread in all the way.

From what I've been learning I wonder if the plastic cup is for a 73mm bb instead of 68.

Ryan
It's possible. I have a Dura Ace track cartridge BB that is around 70mm wide. You are supposed to use [email protected] 1mm spacer on each side or 2mm spacer on the driver side to adjust for small chainline adjustments. Without the spacers, it's the same issue you have. One side or the other sticks out

I ran it for years without spacers and just let the non-drive side cup hang out

On the current bike, I needed the driveside to stick out by 2mm to get a good chainline.
I didn't have metal spacers so I used a rubber o-ring on the drive side as a spacer. It's been working great for a year...
 

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rcnute said:
Yeah, the fixed side will thread in all the way but then the plastic side sticks out pretty far. So I loosened the fixed side, threaded in the plastic side a little further and then tried to tighten the fixed side--but now it won't thread in all the way.

From what I've been learning I wonder if the plastic cup is for a 73mm bb instead of 68.

Ryan
If the BB is for a 73 shell, it would probably also have a longer spindle to match. How do you know you have the right BB in the first place for your frame and cranks?

The last Shimano BB of this type I installed was on a 73mm MTB BB. Starting with the driveside completely tight (which is how you correctly install these), the NDS cup tightened down to flush with the shell. So if your NDS cup sticks out on yours by 5mm, you would have a 73mm BB. The cups aren't really sold separately, if it is just a question of one BB with multiple cups.

In the end, you can probably use this BB with the NDS cup sticking out (NOT the DS) if it has both the right spindle length AND puts your chainrings at the right chainline. The plastic NDS cup isn't going to break if it sticks out a bit.
 

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rx-79g said:
If the BB is for a 73 shell, it would probably also have a longer spindle to match. How do you know you have the right BB in the first place for your frame and cranks?

The last Shimano BB of this type I installed was on a 73mm MTB BB. Starting with the driveside completely tight (which is how you correctly install these), the NDS cup tightened down to flush with the shell. So if your NDS cup sticks out on yours by 5mm, you would have a 73mm BB. The cups aren't really sold separately, if it is just a question of one BB with multiple cups.

In the end, you can probably use this BB with the NDS cup sticking out (NOT the DS) if it has both the right spindle length AND puts your chainrings at the right chainline. The plastic NDS cup isn't going to break if it sticks out a bit.
if you use a cartridge type bb for 73mm shells on a 68 shell it will offset the spindle by 2,5 mm. use a bb spacer and the the non drive cup hang out.
 

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reptilezs said:
if you use a cartridge type bb for 73mm shells on a 68 shell it will offset the spindle by 2,5 mm. use a bb spacer and the the non drive cup hang out.
Sure, if that gives you the correct chainline. But MTB chainline is 47.5, and road triple is 45, so leaving the spacer out makes a certain amount of sense.
 

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reptilezs said:
spindle length determines chainline
Are you saying that putting a 2.5mm spacer under the fixed cup side isn't going to change the chainline? Of course not - the shell and spindle are fixed to each other.

The point here is that we are talking about adapting an MTB BB designed to for a 73mm shell and 47.5 chainline to a 68mm shell and 45mm chainline. Since it is an adaptation of parts not intended for where they are being used, you need actually measure how the parts work out, not just start putting spacers on without knowing why.

The spacer might be necessary, or it might do what I said - push the chainline back out to the MTB standard.
 

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reptilezs said:
crank and spindle will determine the chainline. the spindle is still offset 2.5mm when you butt up the 73 bb in a 68 shell(whole crank is offset the left 2.5mm). some cranks take 113 for std mtb 47.5 other cranks 118, etc.
So it isn't the spindle anymore?

The point here is that for a given crank there is a correct spindle/bb shell width combination. When you try to mix and match parts, like putting a 73mm BB in 68mm shell to use with road triple rather than a MTB triple, you need to account for everything.

We don't know what the OP is doing, why he has the BB he does or what the right stuff should be. But a spacer may or may not be the correct solution to make use of this mystery BB.
 

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rx-79g said:
So it isn't the spindle anymore?

The point here is that for a given crank there is a correct spindle/bb shell width combination. When you try to mix and match parts, like putting a 73mm BB in 68mm shell to use with road triple rather than a MTB triple, you need to account for everything.

We don't know what the OP is doing, why he has the BB he does or what the right stuff should be. But a spacer may or may not be the correct solution to make use of this mystery BB.
for a given crank various spindle lengths will change the chain line. the op doesnt provide enough info to make any calls. just vague info like half the threads here asking for help
 

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The OP last posted a couple hours ago, and since then this thread has gone sideways. Maybe someone should ask him to pull the bottom bracket and look at the label, and put a ruler or a caliper to his BB shell.

OP, what does your bottom bracket say on it? How wide is your shell, really?
 

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Discussion Starter · #20 ·
reptilezs said:
for a given crank various spindle lengths will change the chain line. the op doesnt provide enough info to make any calls. just vague info like half the threads here asking for help
**** you.
 
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