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83mm BB spacing

big-ted

Danced with A, attacked by C, fired by D.
Sep 27, 2005
1,403
46
Vancouver, BC
Can anyone tell me how far apart the cups should be spaced on a Shimano 83mm BB?

For example, the 73mm version has to be spaced 75.5mm, which is why a 73mm shell needs one 2.5mm spacer, a 68 needs 3 spacers etc. The 83mm BB came with 3 spacers but I find it hard to believe the total spacing has to add up to 90.5mm...
 
Oct 14, 2007
394
0
you forget that the spindle length is much greater on the 83mm Crank...treat it basically like if it was a 68mm like you mentioned with 3 2.5mm spacers [depending on your setting]
 

big-ted

Danced with A, attacked by C, fired by D.
Sep 27, 2005
1,403
46
Vancouver, BC
Yeah. Currently I have two spacers and a BB mounted chain device which, in truth, may be a little thicker than 2.5mm. I'm just trying to figure out why my BB had died within about 3 months.
 

khoolhandz

Chimp
Jul 27, 2006
89
0
I LOVE SURREY
Can anyone tell me how far apart the cups should be spaced on a Shimano 83mm BB?

For example, the 73mm version has to be spaced 75.5mm, which is why a 73mm shell needs one 2.5mm spacer, a 68 needs 3 spacers etc. The 83mm BB came with 3 spacers but I find it hard to believe the total spacing has to add up to 90.5mm...
Huh? Didn't know about that. I thought the spacer is simply to give you a better chainline more than anything else.

I have an 83mm BB and don't use any spacers since I don't need to.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,416
969
My own world inside my head
Well, you can vary the chainline by which side you put the spacers, but the total shell length should be fixed.
Well, no actually the spacers are not for chainline. The spacers are going to make your cranks sit evenly on each side, your chain line is going to be figured by spindle length.The spacers are not just for fitting issues, They also offer some protection to the BB cups themselves, you dont want your cups right against the shell, you will usually always see at least one spacer per side. Most 83mm shells will have one spacer on the nondrive side and two ont eh drive side, removing one drive side spacer for use with an Etype mount, either a derailer or chain device. Same for a 68/73 shell setup, 68 has two on the drive side, one on the non drive side, But a 73 shell will have one on each side, removing the driveside spacer when using an etype device..

Problem with most 83mm shells is you dont get much choice at all for chain line.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,416
969
My own world inside my head
Yeah. Currently I have two spacers and a BB mounted chain device which, in truth, may be a little thicker than 2.5mm. I'm just trying to figure out why my BB had died within about 3 months.
This should be correct, with one spacer on the non drive side, and the Chain device and other spacer on the drive side.