JIS Standard Vs "Low Profile" crank tapers

I have an old bike long since converted to a "fixie". He's a solid
old machine with well over 100K behind him. The original "cup & cone"
BB is simply worn out.

It's worth a new BB to get it back on the road, IMO. My issue is that
I currently have the old "JIS Low Profile" taper. I suppose that I
can replace the crank, but I'd prefer not to.

If I go to a standard square JIS taper, will my current crank work?
My LBS says it will; however, I'm not impressed with their knowledge
of obsolete (or "antique", depending on your interpretation) parts.

It looks to me like the JIS low profile taper is identical to the JIS
standard one at the tapered end; however, the low profile taper ends
prematurely in a shoulder. If this is true, then the crank with a low
profile taper would fit on to the end of the standard taper just fine;
however, this would push the chain line outboard... I'm going to guess
about 2mm on each side.

Does anyone have first-hand experience?

Jones... who seeks but to serve God... and to grow wealthy, of course,
as all men.

!Jones wrote:

I have an old bike long since converted to a "fixie". *He's a solid
old machine with well over 100K behind him. *The original "cup & cone"
BB is simply worn out.

It's worth a new BB to get it back on the road, IMO. *My issue is that
I currently have the old "JIS Low Profile" taper. *I suppose that I
can replace the crank, but I'd prefer not to.
[...]
It looks to me like the JIS low profile taper is identical to the JIS
standard one at the tapered end; however, the low profile taper ends
prematurely in a shoulder. *If this is true, then the crank with a low
profile taper would fit on to the end of the standard taper just fine;
however, this would push the chain line outboard... I'm going to guess
about 2mm on each side.

If there is no feature on your cranks that would stop them from being
tightened before they attain a full interference fit on the spindle
taper, then just get a normal JIS bottom bracket and install
everything. If your cranks were sitting hard against the shoulder
before, they'll probably push in just a little father on a non-
shouldered spindle.

For what it's worth, the Shimano BB-UN26 has press-fitted collars that
serve as stops/shoulders (I sometimes remove them), and it costs about
$15. I install these all the time and there have been no unusual
problems with them.

Chalo

On Apr 1, 5:29*pm, Chalo wrote:

For what it's worth, the Shimano BB-UN26 has press-fitted collars that
serve as stops/shoulders (I sometimes remove them), and it costs about
$15. *I install these all the time and there have been no unusual
problems with them.

The UN26 is an interesting bottom bracket, found as standard on a
whole bunch of prestigious and pricey bikes, starting with Gazelle and
relations, like Koga-Miyata. Utopia and other prestigious German
makers are very keen on the even less expensive Kinex bottom bracket.
These are people who have independent tests done on everything that
goes on their bike, and give a ten-year guarantee. So it looks for all
the world as if these experienced manufacturers decided that the
bottom bracket is such a mature technology that there is zero
advantage in splashing out even one step up from the base model by a
reputable manufacturer. In short, the bottom bracket is a commodity
item. -- Andre Jute

On Apr 1, 5:00*pm, "!Jones" wrote:
I have an old bike long since converted to a "fixie". *He's a solid
old machine with well over 100K behind him. *The original "cup & cone"
BB is simply worn out.

It's worth a new BB to get it back on the road, IMO. *My issue is that
I currently have the old "JIS Low Profile" taper. *I suppose that I
can replace the crank, but I'd prefer not to.

If I go to a standard square JIS taper, will my current crank work?
My LBS says it will; however, I'm not impressed with their knowledge
of obsolete (or "antique", depending on your interpretation) parts.

It looks to me like the JIS low profile taper is identical to the JIS
standard one at the tapered end; however, the low profile taper ends
prematurely in a shoulder. *If this is true, then the crank with a low
profile taper would fit on to the end of the standard taper just fine;
however, this would push the chain line outboard... I'm going to guess
about 2mm on each side.

Does anyone have first-hand experience?

Jones... who seeks but to serve God... and to grow wealthy, of course,
as all men.


Yo, Jones, reference to Sheldon Brown's pages will tell you exactly
how far your chain line will move when you switch between crank axle
tapers without changing cranks. I looked into it once, and IIRC, it
was only about 1mm per side, not enough to disturb even a finicky
Rohloff setup.

Kinex bottom brackets offer various tapers and are inexpensive and
good. No idea where you will get them in the States.

And don't Campagnolo bottom brackets come with the taper you want;
over here their lower end BB are sometimes under thirty euro on sale.

-- Andre Jute