What BB do you use with Dura Ace 7400?

[Ugo51]

Hi everyone,

I have a love DuraAce 7400 double crankset that I'd like to put to good use. I had it on my "fast" bike, but I soon found out that is asymmetric, and cannot be matched to a regular cartridge BB. What do you match with this crank to make it work?
I am thinking to either place a 2mm spacer on the DS OR get a cup and cones bottom bracket, which I can easily find with asymmetric spindle.

 

[bikeworkshop]

Shimano cartridge bbs are often not symmetric either, so going a size different can change one side only.

What length did you try?

It's decades since we fitted classic bb cups and axle, and i don't think a 7400 chainset has ever presented a problem.
There's less choice from shimano now though for square taper so you might need old stock.

 

[Ugo51]

I think it might be a 118mm, which is the length I use for my other bike.
It is a bit too much, but I thought that only 107 was asymmetric, and that'd be too short.

 

[bikeworkshop]

We have the advantage of a shelf of every available bb, and quite a few old stock ones, so can just swap out to get the best result.
(Id start with 113)

If you measure crank to Chainstay gap each side with your 118 fitted (deffo too long) you could then get an idea of required axle projection each side, and go to a shop that keeps square taper bbs (if you still have one locally)- to get a decent match. We do this quite a lot.

 

[Ugo51]

I'll have a look in the weekend.

 

[otherself]

7400 English = 112mm, Italian = 113mm

 

[Ugo51]

The problem seems to be that the original 112mm BB was asymmetric and 3mm longer on the DS than the NDS. At least for what I read online.
And I don't seem to be able to source that in a cartridge style.

 

[Jonny69]

I'm pretty sure BBs like the UN55 aren't symmetric either and are longer on the DS. In the past I've just slipped a 2mm spacer onto the drive side to centre the driveline.

 

[Ugo51]

I ended up using a 2.5mm spacer on the drive side.
Works well.
The 118mm BB is actually a good fit. It could be the original dimension was for JIS spindle, while I am using an ISO one. So the 3mm from the spindle + 2.5mm from the spacer compensate for the ISO-JIS difference plus 1mm.