Bicycle Mechanics - Looking for BB spindle advice for two old triple cranks

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bobbotron
03-08-08, 08:44 AM
Hi there,

I'm planning on using an old specialized triple crankset I got from a local bike co op on a bike I'm building up for a friend. It's an old specialized 175mm crank. I'm not sure what the model number is. I'm going to buy a new square taper BB for it, but I'm not sure what length of BB to buy. I've taken a few photos of it below, could you guys/gals help me find the proper BB length for it? I also have a old shimano exage LX 300 crank I'm hoping to put on my mountain bike. I think the correct spindle length for it is 121mm - is that right?

http://www.flickr.com/photos/bobbotron/2318103509/
http://www.flickr.com/photos/bobbotron/2318103507/

The frame the specialized crank is going on.
http://www.flickr.com/photos/bobbotron/2318103511/

Thanks!

Bill Kapaun
03-08-08, 12:28 PM
I've got an 86 RockHopper and the crank On the right resembles it.
I used a 122.5 MM BB. EDIT: make that 122.5 Cartridge
Do you still have the spindles? They might have a code stamped on them like 3P, 3n etc.
My Hopper HAD a 3P, which has the DS of the spindle 3MM longer than the NDS.
I swapped cranks with a 91 TREK. BOTH bikes used the 3P, so I didn't have any problem, but your mileage....
kramnnim
03-08-08, 01:09 PM
The Specialized crank looks like it would use a 113mm spindle...

bobbotron
03-09-08, 08:37 AM
I've got an 86 RockHopper and the crank On the right resembles it.
I used a 122.5 MM BB. EDIT: make that 122.5 Cartridge
Do you still have the spindles? They might have a code stamped on them like 3P, 3n etc.
My Hopper HAD a 3P, which has the DS of the spindle 3MM longer than the NDS.
I swapped cranks with a 91 TREK. BOTH bikes used the 3P, so I didn't have any problem, but your mileage....

Hmm. I got both cranks from a local bike co op, they didn't come with a BB.

Are you sure it was a 122.5 mm bb? According to sheldon's site, the Exage 300LX M300 takes a 121 mm bb. Hmm.
bobbotron
03-09-08, 03:49 PM
So, I did a bit of searching and I think the specialized crank is a specialized Strongarm. Anyone know what BB length the strongarms take?
Bill Kapaun
03-09-08, 06:22 PM
Hmm. I got both cranks from a local bike co op, they didn't come with a BB.

Are you sure it was a 122.5 mm bb? According to sheldon's site, the Exage 300LX M300 takes a 121 mm bb. Hmm.

Both bikes used the "P" spindle, which has 3mm additional length on the DS. Its total length is 119mm.
Since I was replacing one with a cartridge BB, which is basically symmetrical, I needed 3MM longer.
My chain line turned out near perfect, as far as my eye can tell. Middle ring lines up in the middle of the cassette.
That said, I had to make a slight adjustment to the Fder's on both bikes. THERE IS some difference between cranks. I don't think the 'Hopper crank had been off the bike and the one on my TREK looked like it had been off "several" times. Maybe it slid on more than it should have?

Also, consider the difference between 121 & 122.5 It's only .75MM per side. That's .030"!