Which cartridge Bottom Bracket for 1992 Specialized Hard Rock?
10-27-22, 05:20 PM
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Which cartridge Bottom Bracket for 1992 Specialized Hard Rock?
I need to replace the bottom bracket on my 1992 Specialized Hard Rock and I'm not quite sure what size or model to get. When I measured the spindle with my calipers I came up with 124mm. When I measured the painted part of the frame with my tape measure I got 2 5/8" which is about 66.6mm. I had a tough time getting an accurate measurement with the tape measure. Can anyone point me towards a good affordable replacement cartridge bottom bracket?
I'm seeing the UN55 and UN300 as popular choices but I'm nervous about choosing the incorrect size. Thank you!
I'm seeing the UN55 and UN300 as popular choices but I'm nervous about choosing the incorrect size. Thank you!
10-27-22, 05:43 PM
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It looks like you need a 124mm spindle probably JIS taper. However your cranks determine all of this not so much the bike. I would look at the Interloc Racing Designs they make excellent BBs
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10-27-22, 06:45 PM
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Any other markings on the spindle like 3S or 3NN?
Do "A" and "C" measure the same? See diagram here
https://www.sheldonbrown.com/bbsize.html
Do "A" and "C" measure the same? See diagram here
https://www.sheldonbrown.com/bbsize.html
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10-27-22, 07:28 PM
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You have a 68mm bottom bracket shell. Table of BB spindle sizes by Sheldon Brown lists symmetric equivalents. As veganbikes says, most likely you have a symmetric 124mm one.
There is also JIS vs ISO difference, both UN55 and UN300 are JIS.
Edit: dedhed beat me.
There is also JIS vs ISO difference, both UN55 and UN300 are JIS.
Edit: dedhed beat me.
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10-27-22, 07:56 PM
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Any other markings on the spindle like 3S or 3NN?
Do "A" and "C" measure the same? See diagram here
https://www.sheldonbrown.com/bbsize.html
Do "A" and "C" measure the same? See diagram here
https://www.sheldonbrown.com/bbsize.html
Would this Shimano UN300 BSA 68MM, Spindle 122.5MM be compatible? I'm wondering if losing 1.5mm in length would be problematic?
https://www.amazon.com/gp/product/B0...ustomerReviews
10-27-22, 09:57 PM
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Would this Shimano UN300 BSA 68MM, Spindle 122.5MM be compatible? I'm wondering if losing 1.5mm in length would be problematic?
https://www.amazon.com/gp/product/B0...ustomerReviews
https://www.amazon.com/gp/product/B0...ustomerReviews
According to the chart your 3NN has a 124mm spindle, which means it protrudes by (124-68)/2=28mm on each side.
Is UN300 symmetric? Does Shimano have a drawing for it? Something like this old Tange catalog (see the last page) - their 122 is non-symmetric with 28 on the right (what you need) and 26 on the left (should probably be OK, use a pedal washer if you need it).
I think square taper cranksets are pushed further onto the BB every time they are removed/reinstalled, which effectively changes the spindle length. Also, what is the tolerance the BBs are made to? My guess is that you will be OK.
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10-27-22, 10:46 PM
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1.5mm is only 0.75mm per side. Most applications that's "close enough"
Does your chain ring/crank arm clear the chainstay by enough to move in a mm or so?
Riv shows non symmetrical with shift to the R options
https://www.rivbike.com/products/car...nt=38265581965
Does your chain ring/crank arm clear the chainstay by enough to move in a mm or so?
Riv shows non symmetrical with shift to the R options
https://www.rivbike.com/products/car...nt=38265581965
Last edited by dedhed; 10-27-22 at 10:49 PM.
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10-28-22, 08:48 AM
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I need to replace the bottom bracket on my 1992 Specialized Hard Rock and I'm not quite sure what size or model to get. When I measured the spindle with my calipers I came up with 124mm. When I measured the painted part of the frame with my tape measure I got 2 5/8" which is about 66.6mm. I had a tough time getting an accurate measurement with the tape measure. Can anyone point me towards a good affordable replacement cartridge bottom bracket?
I'm seeing the UN55 and UN300 as popular choices but I'm nervous about choosing the incorrect size. Thank you!
I'm seeing the UN55 and UN300 as popular choices but I'm nervous about choosing the incorrect size. Thank you!
You should be able to find any number of BB-UN300 bottom brackets for around $15 on line. As there isn’t a 124mm spindle in that model, you’ll have to use the 122.5 mm. You will need to make some minor adjustments to the limit screws.
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10-28-22, 08:46 PM
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You have a set of calipers, why not use them to measure the bottom bracket shell? It’s a whole lot easier than trying to use a tape measure. The bottom bracket shell is 68mm, by the way.
You should be able to find any number of BB-UN300 bottom brackets for around $15 on line. As there isn’t a 124mm spindle in that model, you’ll have to use the 122.5 mm. You will need to make some minor adjustments to the limit screws.
You should be able to find any number of BB-UN300 bottom brackets for around $15 on line. As there isn’t a 124mm spindle in that model, you’ll have to use the 122.5 mm. You will need to make some minor adjustments to the limit screws.
I ended up up ordering a Tange LN3922 68x122 - I'm looking forward to installing it.
10-28-22, 08:56 PM
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Good question...
According to the chart your 3NN has a 124mm spindle, which means it protrudes by (124-68)/2=28mm on each side.
Is UN300 symmetric? Does Shimano have a drawing for it? Something like this old Tange catalog (see the last page) - their 122 is non-symmetric with 28 on the right (what you need) and 26 on the left (should probably be OK, use a pedal washer if you need it).
I think square taper cranksets are pushed further onto the BB every time they are removed/reinstalled, which effectively changes the spindle length. Also, what is the tolerance the BBs are made to? My guess is that you will be OK.
According to the chart your 3NN has a 124mm spindle, which means it protrudes by (124-68)/2=28mm on each side.
Is UN300 symmetric? Does Shimano have a drawing for it? Something like this old Tange catalog (see the last page) - their 122 is non-symmetric with 28 on the right (what you need) and 26 on the left (should probably be OK, use a pedal washer if you need it).
I think square taper cranksets are pushed further onto the BB every time they are removed/reinstalled, which effectively changes the spindle length. Also, what is the tolerance the BBs are made to? My guess is that you will be OK.
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10-29-22, 08:56 AM
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The reading on the caliper isn’t 68mm but that doesn’t matter for a bottom bracket. You don’t need to have two decimal place precision since the common sizes are 68mm and 73mm with 68mm being far more common than 73mm. Honestly, I think I’ve only ever owned one bike with a 73mm bottom bracket out of 50 bikes (mine, my wife’s, and my kids).
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Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
10-29-22, 09:01 AM
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Just a tip on measuring things with calipers where there is interference with the jaws. The little metal strip in the middle of the main scale is called a depth gauge. Line the end of the caliper up with one side and run the depth gauge out the where you need to measure. Pictures are better
The reading on the caliper isn’t 68mm but that doesn’t matter for a bottom bracket. You don’t need to have two decimal place precision since the common sizes are 68mm and 73mm with 68mm being far more common than 73mm. Honestly, I think I’ve only ever owned one bike with a 73mm bottom bracket out of 50 bikes (mine, my wife’s, and my kids).
The reading on the caliper isn’t 68mm but that doesn’t matter for a bottom bracket. You don’t need to have two decimal place precision since the common sizes are 68mm and 73mm with 68mm being far more common than 73mm. Honestly, I think I’ve only ever owned one bike with a 73mm bottom bracket out of 50 bikes (mine, my wife’s, and my kids).
10-29-22, 02:47 PM
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I couldn’t live without it! I use it for all kinds of things like replacing broken axles where you need to get the cones set evenly on both sides of the axle.
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Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Stuart Black
Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
