On Thursday, June 15, 2017 at 7:21:03 AM UTC-7, wrote:
On Wednesday, June 14, 2017 at 11:54:46 PM UTC-7, John B. wrote:
On Wed, 14 Jun 2017 20:38:04 -0500, AMuzi wrote:

On 6/14/2017 5:28 PM, James wrote:
On 15/06/17 06:31, Joerg wrote:
On 2017-06-13 19:09, John B. wrote:

In a recent discussion I suggested changing from the old
square
tapered BB to a modern Shimano outboard bearing bracket.
The argument
was that this would destroy the perfect chain line of the
original
three piece BB.

Now, I have changed back and forth between the original
square tapered
axle to the outboard bearing BB and to my recollection
the chain line
didn't seem to change noticeably.

Over the weekend we took a trip "up country" to visit
some of my
wife's relatives and as we used my wife's car she drove.
It is about
250 Km, one way, so I had a lot of time to think abut
things and one
of the things I thought about was how could I change
bottom brackets
with no appreciable difference in chain line.

This morning I turned one of my bikes bottom up and did
some measuring
and it turns out that with the old fashioned three piece
BB there is
slightly over 10mm clearance between the inner edge of
the crank arm
and the outer edge of the BB. The outboard bearing
"flanges" measured
12mm in thickness and the old sty;e BB flange is `1mm..

Thus the changing from the old style to the more modern
BB results in
very little, if any, difference in chain line. Certainly
less then the
difference between two cogs on the cassette.

Granted that bicycles are all different but the above
does explain why
I, after switching from one type to the other, and back
again, have
seen no noticeable difference in chain line.


The discussion you were referring to was about Shimano 600
gear which is
what I have on my road bike. The clearance from the inner
edge of the
drive side crank to the outer surface of the BB is 3mm.
Now assume your
12mm measurement minus the 1mm that the regular cartridge
BB has. That's
already 11mm of chain line offset. A lot. You could reduce
the clearance
to 2mm but that much wiggle room you really need for
square taper and
that would still leave you with a chain line 10mm off from
where it was.


On my previous frame, I migrated from Campagnolo square
tapered BB & cranks to Campagnolo outboard bearing BB assy,
and the chain line didn't shift 10mm.

Why do you think you are special?


Chainline errors are entirely from not using the
manufacturer's specified parts.

Only a complete idiot would pull a functional spark plug
from a V8 and drop it into a 4-cyl Asian econobox. Yet
people mix arms and spindles which are ridiculously
incompatible every day and then ride over here to complain
that the crank's no good. Oy!

p.s. Almost all derailleur systems will work well with
+1mm/-1mm chainline error. Few can accept 10mm either way,
that is a very large distance.

I think I would have to be a bit picky here. A Big chain ring to a
small cassette cog is going to be about 21 mm out of line, assuming
that the chain line was initially aligned, big ring to 5th cog of a 9
speed cassette, and it still shifts.

But, of course, if the chain line was initially 10 mm out of alignment
then certainly shifting would be a bit "iffy" at least in one
direction :-)

On a triple the middle ring is aligned with the 5th cog.

Not on a Fuji
http://www.classicfuji.com/1981_Thumbs.htm