BB spec-check

[kolchek]

Hi everyone,

I'm not 100% bike-tech savvy but here goes: My BB needs replacing [play & a bit crunchy], the specs on the stock one are 68 x 124.5. The current chainline is about 50 mm. Seat-tube diameter is 34mm. The clearance between frame & chainring now is 2 mm max. The largest chainring is mounted outside the spider, the 2 smaller are inside.

The closest BB's to 124.5mm I've found are 122.5mm & 127mm. I'm not quite sure how spacers work, but if I use the 122.5 & move the chainring 1 or 2mm out that should be about spot on. Will a spacer do the trick? I can't quite figure out where a spacer fits/how it works.

Thanks all - & nice to be here.

K

 

[vspa]

complete info here

http://www.sheldonbrown.com/bbsize.html

 

[kolchek]

Thanks, I'd already read through that but there's no BB listed with the dimensions I require, & no info about adapting a different sized BB to suit, if I'm not mistaken.

Ta.

 

[Steve_A]

Call Velo Orange. They sell BBs and shims, and mentioned on a blog entry that they had advised someone on using shims. I bet they can help you.

 

[vspa]

try with your LBS, looks like you need a custom fit & repair

 

[alfeng]

Originally Posted by kolchek .

I'm not 100% bike-tech savvy but here goes: My BB needs replacing [play & a bit crunchy], the specs on the stock one are 68 x 124.5. The current chainline is about 50 mm. Seat-tube diameter is 34mm. The clearance between frame & chainring now is 2 mm max. The largest chainring is mounted outside the spider, the 2 smaller are inside.

The closest BB's to 124.5mm I've found are 122.5mm & 127mm. I'm not quite sure how spacers work, but if I use the 122.5 & move the chainring 1 or 2mm out that should be about spot on. Will a spacer do the trick? I can't quite figure out where a spacer fits/how it works.

FWIW. IMO, it's probably better to have the crankarms 1.25mm [COLOR= #008000]wider[/COLOR] than 1.0mm [COLOR= #ff0000]narrower[/COLOR], particularly since your chanring clearance is so tight.

But, measure your BB spindle again ... and then, a third time.

FYI. BB spacers sleeve onto the BB cup & fit between the BB shell & the inner edge of the fixed cup to move the driveside away from the bike's center line.

BTW. If the search becomes too tedious OR expensive, then simply consider a new crank-and-BB combination ...

• you'll get a set of new chainrings in the process ...
• if the new crankset that you choose uses the same chainring BCD size, then you can use your old rings, first

 

[Peter@vecchios]

Originally Posted by kolchek .


Hi everyone,

I'm not 100% bike-tech savvy but here goes: My BB needs replacing [play & a bit crunchy], the specs on the stock one are 68 x 124.5. The current chainline is about 50 mm. Seat-tube diameter is 34mm. The clearance between frame & chainring now is 2 mm max. The largest chainring is mounted outside the spider, the 2 smaller are inside.

The closest BB's to 124.5mm I've found are 122.5mm & 127mm. I'm not quite sure how spacers work, but if I use the 122.5 & move the chainring 1 or 2mm out that should be about spot on. Will a spacer do the trick? I can't quite figure out where a spacer fits/how it works.

Thanks all - & nice to be here.

K

Get the 127, install on dry spindles to 30 ft lbs. Each side is only 1.5mm longer or so. Don't shim or anything like that, not necessary. The 122 will result in the CR hitting the frame.

 

[kolchek]

Thanks all,

I really appreciate your attention & advice. The 127 seems the way to go.

Cheers.