Crankset/bottom bracket question....HELP PLEASE

[nelsonccc]

Crankset/bottom bracket question....HELP PLEASE

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So I'm building up a SS using an Origin 8 scout 29 steel frame (that I got on here and it's awesome). I want to re-use my old ghetto cranks from my Specialized Hardrock. They are a octalink V2 suntour crank. Although with a raceface ring installed they only weigh 580grams.

Anyways, my old BB was a 68x118. The Origin 8 frame takes a 73mm bb. So I need a new BB. The question is do I need to grow the spindle length since it's now 73 instead of 68? Or would I just buy a 73x118 BB? My thinking is that if the shell is wider (73mm) but the spindle stays at 118 long then won't the cranks get 'pulled' in too close to the frame? If i want to keep roughly the same chainline do I need to grow the 118 spindle length the same proportion as from 68 to 73? So should I be looking at a 73xsomething longer than 118?

I know it's a lot of questions but I'm trying to figure it out. I've read a bunch of stuff but no-one seems to answer whether the spindle length grows with the change from 68 to 73.

Thanks in advance!

I've put up a couple pics of the old BB and the build as is now. I've got the crank and chain so It's almost ready to GO!.

[DOSS]

Sounds like you need to pick up a 73X122 BB.... 121 should work for you as well http://www.amazon.com/Shimano-BB-ES5.../dp/B007FP66CO

[nelsonccc]

After doing some more research and some help form the guys over at MTBR. I put the 68x118mm BB into the drive side which would simulate (as I understand it) a 123mm spindle in my 73mm shell. Looks like the chainline will be about 50mm and probably 1-2mm too far out in relationship to the rear cog. Hard to tell though.

I think that a 73x121 might be the way to go. Looks like that will give me a 48mm chainline while still providing enough clearances for the crank arms.

[Yuup]

Can't you just adjust the rear sprocket to compensate?

[nelsonccc]

Nope. Fixed location on SS specific rear hub.