[Bullit21]

Is it possible to fit a 73mm Bottom bracket in a 68mm shell? If it is possible, what are the steps? Thanks for the input.

 

[J5ive]

You can usually get away with a few spacers under the bb cup. I'm guessing its an ISIS bb? The spacers used are the same as those used to space cassettes (say when running a 7speed on 9 speed hub).

 

[Jm_]

you may have problems shifting if this is a bike with a front derailer, spacers go on the drive side usually, as the cup is on the non-drive side..

 

[Sideways]

Put a 2.5mm BB spacer between the frame and the drive side BB cup.

 

[Sir_Crackien]

do what sideways said. i have done that twice and it works perfectly.

i.e. no der. or chain line problems

 

[Bullit21]

Thanks guys. I have everything installed now with one spacer on the drive side, but the non-drive side is not screwed all the way into the BB shell, about 3 of the BB threads are still exposed. The cranks seem to be evenly spaced on either side of the shell, the non-drive crank is clearing the chain stay by about 1/4 to 1/2 inch and it is pedaling and shifting fine right now. Will the exposed threads put too much strain on the BB from a weight distribution perspective? I am running two rings with a bash, if this helps at all. Thanks again.

 

[Bullit21]

Buehler, Buehler, anyone? Somebody has to have experienced the exposed threads too?

 

[Brian HCM#1]

Thanks guys. I have everything installed now with one spacer on the drive side, but the non-drive side is not screwed all the way into the BB shell, about 3 of the BB threads are still exposed. The cranks seem to be evenly spaced on either side of the shell, the non-drive crank is clearing the chain stay by about 1/4 to 1/2 inch and it is pedaling and shifting fine right now. Will the exposed threads put too much strain on the BB from a weight distribution perspective? I am running two rings with a bash, if this helps at all. Thanks again.

3 threads you should be fine, most of the load is on the drive side, make sure that side has enough threads.

 

[Matt D]

Exposed threads? So that would mean that when you tighten that side you're merely going against the bearing, not the frame. I would guess you're not going to get the correct preload on the bearings and could cause premature failure. Why not put in another spacer?

 

[Brian HCM#1]

Actually some 68/73mm BB's come with a locknut just for exposed nondrive threads.