Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Shimano UN-73 NDS cup: Can I substitute with any other UN cup?

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Shimano UN-73 NDS cup: Can I substitute with any other UN cup?

Old 06-20-23, 12:44 PM
  #1  
Senior Member
Thread Starter
 
Piff's Avatar
 
Join Date: Nov 2013
Location: Southern California
Posts: 1,472
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 802 Post(s)
Liked 760 Times in 413 Posts
Shimano UN-73 NDS cup: Can I substitute with any other UN cup?

I have a UN-73 bottom bracket that I am planning to install on my bike. In order for the spindle to match the cranks I placed a 1.5mm spacer inbetween the frame and the drive side cup. The bottom bracket has a plastic NDS cup with a lip, and I'm worried that it isn't threaded in as much as it could/should be. There isn't any discernable play when I wiggle the spindle, but I'm afraid that when standing up and pedaling up a hill there might be an issue.

Can I simply grab another shimano cartridge bottom bracket NDS cup w/o a lip and use that no problem? Or are the UN-7x and UN-5x bottom brackets different enough that it won't work?

Thanks!
Piff is offline  
Old 06-20-23, 01:42 PM
  #2  
working on my sandal tan
 
ThermionicScott's Avatar
 
Join Date: Aug 2011
Location: CID
Posts: 22,638

Bikes: 1991 Bianchi Eros, 1964 Armstrong, 1988 Diamondback Ascent, 1988 Bianchi Premio, 1987 Bianchi Sport SX, 1980s Raleigh mixte (hers), All-City Space Horse (hers)

Mentioned: 98 Post(s)
Tagged: 0 Thread(s)
Quoted: 3873 Post(s)
Liked 2,574 Times in 1,581 Posts
Originally Posted by Piff
Can I simply grab another shimano cartridge bottom bracket NDS cup w/o a lip and use that no problem? Or are the UN-7x and UN-5x bottom brackets different enough that it won't work?

Thanks!
I believe it should be compatible, and worth doing! People raised on loose-ball bottom brackets (which is most people in C&V) don't always get that the important thing with these cartridge bottom brackets is for the NDS cup to engage solidly with the left side of the cartridge -- not the left edge of the bottom bracket shell. So they worry about gaps between the NDS cup and the shell and attempt to close them with spacers.

Problem Solvers used to make a nice lipless NDS cup for this application. It's out of production, but it looks like there are a few out there in the supply chain: https://www.freewheelbike.com/produc...p-182478-1.htm
__________________
Originally Posted by chandltp
There's no such thing as too far.. just lack of time
Originally Posted by noglider
People in this forum are not typical.
RUSA #7498

Last edited by ThermionicScott; 06-20-23 at 01:46 PM.
ThermionicScott is offline  
Old 06-20-23, 02:15 PM
  #3  
Senior Member
Thread Starter
 
Piff's Avatar
 
Join Date: Nov 2013
Location: Southern California
Posts: 1,472
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 802 Post(s)
Liked 760 Times in 413 Posts
Originally Posted by ThermionicScott
I believe it should be compatible, and worth doing! People raised on loose-ball bottom brackets (which is most people in C&V) don't always get that the important thing with these cartridge bottom brackets is for the NDS cup to engage solidly with the left side of the cartridge -- not the left edge of the bottom bracket shell. So they worry about gaps between the NDS cup and the shell and attempt to close them with spacers.

Problem Solvers used to make a nice lipless NDS cup for this application. It's out of production, but it looks like there are a few out there in the supply chain: https://www.freewheelbike.com/produc...p-182478-1.htm
Luckily I already have a cruddy UN-51 from which to steal a lipless NDS cup. Fit like a glove! And screwed in farther than the lipped one that it replaced, so, as you said, definitely worth doing. I'll of course update if something goes wrong down the line, but based on how it felt installing compared to other cartridge bottom brackets, I think it's good to go
Piff is offline  
Likes For Piff:
Old 06-20-23, 02:42 PM
  #4  
Senior Member
 
maddog34's Avatar
 
Join Date: Jul 2015
Location: NW Oregon
Posts: 2,986

Bikes: !982 Trek 930R Custom, Diamondback ascent with SERIOUS updates, Fuji Team Pro CF and a '09 Comencal Meta 5.5

Mentioned: 15 Post(s)
Tagged: 1 Thread(s)
Quoted: 1301 Post(s)
Liked 744 Times in 538 Posts
Originally Posted by Piff
Luckily I already have a cruddy UN-51 from which to steal a lipless NDS cup. Fit like a glove! And screwed in farther than the lipped one that it replaced, so, as you said, definitely worth doing. I'll of course update if something goes wrong down the line, but based on how it felt installing compared to other cartridge bottom brackets, I think it's good to go
That "glove" fit may be a false victory.. it may have been the threads bottoming out in the frame...

Two things to look at before installing the different NDS cup...

are the cup's threads short enough that they won't bottom out in the frame's threads? TEST FIT the NDS cup with no Drive Side assy. in place. See if it binds up at the same depth as when the entire assy. was installed....... some careful trimming of length might remedy any interference.... be mindful of those fine rate threads though, or you may ruin the cup.

also.. slip the cup onto the BB assy to see if it is a good snug fit... it should take a bit of a push to make it fit onto the bearing housing... if it's loose, and doesn't take light force to fit all the way on, it will not work out well. Extra-tight slip fit is better than a loose fit, and since you've moved the engagement depth 1.5 mm, well, you'll be needing every bit of "snug" it has to offer....

and be aware that either one of these factors will directly alter the other factor, and the final installed depth of the NDS cup....

Not trying to rain on the parade, but just prevent the marching band from playing out of tune...

Last edited by maddog34; 06-20-23 at 02:59 PM.
maddog34 is offline  
Likes For maddog34:
Old 06-20-23, 03:02 PM
  #5  
Senior Member
Thread Starter
 
Piff's Avatar
 
Join Date: Nov 2013
Location: Southern California
Posts: 1,472
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 802 Post(s)
Liked 760 Times in 413 Posts
Originally Posted by maddog34
That "glove" fit may be a false victory.. it may have been the threads bottoming out in the frame...

Two things to look at before installing the different NDS cup...

are the cup's threads short enough that they won't bottom out in the frame's threads? TEST FIT the NDS cup with no Drive Side assy. in place. See if it binds up at the same depth as when the entire assy. was installed....... some careful trimming of length might remedy any interference.... be mindful of those fine rate threads though, or you may ruin the cup.

also.. slip the cup onto the BB assy to see if it is a good snug fit... it should take a bit of a push to make it fit onto the bearing housing... if it's loose, and doesn't take light force to fit all the way on, it will not work out well. Extra-tight slip fit is better than a loose fit, and since you've moved the engagement depth 1.5 mm, well, you'll be needing every bit of "snug" it has to offer....

and be aware that either one of these factors will directly alter the other factor, and the final installed depth of the NDS cup....

Not trying to rain on the parade, but just prevent the marching band from playing out of tune...

Hmmmm, good points. I have yet to remove the bottom bracket and take a look at how the replacement NDS fits onto the UN73 shell, but the UN73 NDS cup fits awfully easily on the UN-51. So...that would suggest that the replacement NDS cup should either fit fine on the UN-73, or it might crack once installed.

Good idea on checking to see when the NDS cup begains to bind w/o the bottom bracket installed.

Better safe than sorry!
Piff is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.