Campagnolo bottom bracket Help

[Mccarti]

Wonder if anyone can help or guide me in the right direction.

I have an early 80's Colnago which has 126mm rear spacing and Italian bottom bracket threads. It is fitted with an early 80s Campag SR front derailleur.

I also have a mid 70s Campagnolo SR chainset which I think was probably designed to run with 120mm rear spacing. This used a 113mm bottom bracket.

Late in the 70s I understand Campagnolo redesigned the SR chainset to allow for a redesigned and wider font derailleur. Accordingly the bottom bracket was lengthened to 116mm.

Any ideas what would be the best bottom bracket length to combine the 80s Colnago frame and Campagnolo front derailleur with the 70s chainset ? Or a (simple) way of working it out ?

Thanks for your help

 

[bm0p700f]

My instincts would be to fit a BB and your crankset and look for a length that give a chain line of 43.5mm.

 

[Mccarti]

Thanks bm0p,

I think its going to be an afternoon in the shed and a bit of trial and error !

Rgds

 

[nammonk]

I think the main problem with the 70s BB/chainset is going to be hitting the lip on the 80s mech. It might be as simple as swapping in the longer axle --- this should help with the chainline as well. If so, it might be worth having a look at wblenkin's Campag spares sale on lfgss --- he has a range of used axles in this week. I don't know if they changed the cups at all when they lengthened the axle, but I'm sure someone here does.
You could always see if there is someone who would swap a 70s chainset for an 80s... More of the later ones are still around.

Nick

 

[Mccarti]

Thanks Nick,

I have an 80s chainset which I can fit if I cannot make this combo work. I actually got the chainset from Wayne - it is pantographed Colnago, so would look nice on the Colnago frame.

If it doesn't work with this build I will be looking for a 70s Colnago frame and derailleur.

Rgds

 

[nammonk]

Well, it looks like Wayne has the longer axle (SS?) so maybe just that would do the trick? Unfortunately, I don't have a 70s Colnago to offer...
Nick

 

[Mccarti]

Cheers Nick. will check it out.