# Internal/External bottom bracket compatibility?



## YZINGERR (Aug 19, 2007)

I am doing a build up with a Nashbar mountain frame.
My old crank and bb is a truvativ iso flow 3x crankset and a VP internal sealed square taper cartridge bb.
The Nashbar frame is able to accept external thread in cups, but I assume that makes my old crankset unuseable for this build?
I'm trying to reuse as much as possible because i'm broke.
Help!


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## Squash (Jul 20, 2003)

You are correct. An external BB is not compatible with your old crank set. A external bearing BB has no spindle. They are simply bearing cups that hold sealed bearings with a 24mm I.D. inner race. The spindle is actually permanently attached to one of the crank arms. The spindle is inserted through the BB and then the non-permanent crank arm is bolted in place. There's a little more to it than that of course. But that's the general idea. So, yeah, if you wanted to go with an external bearing BB you'd need a compatible crank set to use with it.

Good Dirt


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## thomllama (Oct 3, 2007)

what Squish said.. :thumbsup:


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## mack_turtle (Jan 6, 2009)

i may have missed something, but you can use your old BB and your old crank with this frame. unless the frame is made for press-fit bottom brackets, the threads for external (Shimano Hollowtech, SRAM GXP, FSA MegaExo, etc) and internal square-taper and Octalink and Isis BBs are the same. the only difference is that external BBs leave the bearings outside the frame and use a crank made specifically with that BB and more traditional BBs fit the bearings inside the frame. if you have have to replace the BB on a ST crank, be sure to get the correct length to go with that crankset.

for example, my old Redline frame came with Truvativ ST cranks and I replaced them with a Truvativ Stylo GXP crank and BB, no problem. make sure you use the right number and size of spacer on the BB though.


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## Harold (Dec 23, 2003)

mack_turtle said:


> i may have missed something, but you can use your old BB and your old crank with this frame. unless the frame is made for press-fit bottom brackets, the threads for external (Shimano Hollowtech, SRAM GXP, FSA MegaExo, etc) and internal square-taper and Octalink and Isis BBs are the same. the only difference is that external BBs leave the bearings outside the frame and use a crank made specifically with that BB and more traditional BBs fit the bearings inside the frame. if you have have to replace the BB on a ST crank, be sure to get the correct length to go with that crankset.
> 
> for example, my old Redline frame came with Truvativ ST cranks and I replaced them with a Truvativ Stylo GXP crank and BB, no problem. make sure you use the right number and size of spacer on the BB though.


if the OP still has that old BB, then yeah, it'll work with the old cranks on this frame.

I do prefer the external bearing bb and crank setup over the old style but if you're doing a budget build and you've got the old parts, use 'em. you can always change that stuff later.


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## YZINGERR (Aug 19, 2007)

Thank you guys for the great info!

I have been doing research and can't find a straight answer.
Can I use a shimano square taper bb with my truvativ square taper cranks?
I read somewhere that there are 2 incompatible types of square tapered arms


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## mack_turtle (Jan 6, 2009)

ST interfaces are all the compatible. just make sure you find out what width you need for that crankset or it will badly mess up your chainline. they come in widths from about 107 mm(?) to 126mm or so.

off the top of my head, here are the main mtb bottom bracket/crank standards, most of which are no compatible.

square taper
Isis
Octalink
Hollowtech (Shimano)
MegaExo (FSA)
GXP (Sram/Truvativ)

the first three are cartridge/ internal bottom brackets and the second are external bearings. all of these can be put in a standard threaded bottom bracket.


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## YZINGERR (Aug 19, 2007)

Thanks Mack


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