Cartridge BB spindle length compatibilty

Quoted message said:

I'm upgrading the cup and cone BB in my super light weight,
incredibly sexy and fast (well compared to all my other bikes
anyway) Shogun Tri- sport 14 speed road bike. The Shimano
Exage 300EX cranks, rear dérailleur and hubs date it to the
early 90's I think.

Anyway, I measured the old BB spindle to be 119.87mm, so lets
call it 120mm. This was confirmed by info on the late, great
Sheldon Brown's website after I pulled the spindle out and
matched the 3N marked on the spindle to the table on his site:
http://sheldonbrown.com/bbsize.html The LBS didn't know what I
was talking about when I said the spindle was 120mm (I
neglected to mention that it wasn't a cartridge BB so this may
have caused them confusion) and offered me 118mm or 122mm
replacements.

In the end I took the spindle in to them, they measured it at
119mm and recommended a 118mm cartridge replacement which I
bought. After mulling it over for a while, I'm now concerned
that the inner ring may foul on the chainstay (though
obviously I'm yet to try it) and there's the issue of
chainline, but I'm going to be out by + or - 2mm either
way depending on if I use a 118mm or a 122mm BB. Apart from
rebuilding the cup and cone BB which I'd rather not do, what
should I do? Is 2mm that big of a deal when it comes to
chainline?

2mm difference overall would be 1mm each side, and that's as
close as you can hope to get.

But there's another issue. Modern sealed square-taper BBs are
symmetrical. Sheldon says yours is asymmetrical. He goes on
to suggest 124mm as the symmetrical equivalent (to get the
chainwheel side correct). This will move the LH crank further
out, but that won't be an issue.

I haven't seen 124mm JIS square taper BBs available, so
122/122.5 is likely to be what you want (only 1mm shorter on
the RH side).

John

John Henderson said:

2mm difference overall would be 1mm each side, and that's as
close as you can hope to get.

But there's another issue. Modern sealed square-taper BBs are
symmetrical. Sheldon says yours is asymmetrical. He goes on
to suggest 124mm as the symmetrical equivalent (to get the
chainwheel side correct). This will move the LH crank further
out, but that won't be an issue.

I haven't seen 124mm JIS square taper BBs available, so
122/122.5 is likely to be what you want (only 1mm shorter on
the RH side).

John

Hmm, thanks John I failed to read Sheldon's page thoroughly enough.
The longest that the LBS has in stock is 122mm so I think I will take
it back and swap it for that.

lemmiwinks said:

I'm upgrading the cup and cone BB in my super light weight, incredibly
sexy and fast (well compared to all my other bikes anyway) Shogun Tri-
sport 14 speed road bike. The Shimano Exage 300EX cranks, rear
dérailleur and hubs date it to the early 90's I think.

Bah! What would you want to ride such a heavy, slow, low-spec old
thing for? ;-)

BTH

BT Humble said:

lemmiwinks said:

I'm upgrading the cup and cone BB in my super light weight, incredibly
sexy and fast (well compared to all my other bikes anyway) Shogun Tri-
sport 14 speed road bike. The Shimano Exage 300EX cranks, rear
dérailleur and hubs date it to the early 90's I think.

Bah! What would you want to ride such a heavy, slow, low-spec old
thing for? ;-)

BTH

:-D

We're a perfect match that bike and I.