Re: Headset race fit / snugness

[Zog The Undeniable]

Retro Bob wrote:

> If a headset fork race is spec'ed at 26.4, is the fork itself supposed
> to be 26.4 or a little oversize ? That is, if both the fork and race
> are exactly 26.4, it will sit loose, so either the fork should be over
> a little or the race, correct ? What's the tradition ?
> Same question for the crown race ? If the spec is 30.2, is the cup
> itself a little oversize ? Or is the head tube a little undersize ?
>
> Did the Italians have their own standard for headset dimensions 20
> or so years ago ?
>
> As you might guess, I am trying to diagnose why a headset that
> should fit is loose. Something is wrong, but I'm not sure which
> part should be at which spec.

The races are always an interference fit on the frame and fork, i.e. the
crown race is a little smaller than the fork crown and the cups are a
little larger than the head tube. This means that things are stretched
slightly when fitted, which keeps them in place.

The sizes are here, and the 1" ISO size is "Campagnolo" standard:

http://www.sheldonbrown.com/gloss_h.html#headset

The Japanese used to have their own JIS sizes but modern bikes use the
ISO standard.

 

[Jim Adney]

On Thu, 07 Oct 2004 20:25:56 +0100 Zog The Undeniable
<[email protected]> wrote:

>The sizes are here, and the 1" ISO size is "Campagnolo" standard:
>
>http://www.sheldonbrown.com/gloss_h.html#headset

This is a nice collection of info, but it only gives the headset
dimensions. It would be even more useful if it also gave the
dimensions for the mating part on the frame and fork. I think that's
what the OP wanted to know.
-
-----------------------------------------------
Jim Adney [email protected]
Madison, WI 53711 USA
-----------------------------------------------

 

[Dan Daniel]

On Thu, 07 Oct 2004 22:35:52 -0500, Jim Adney <[email protected]>
wrote:

>On Thu, 07 Oct 2004 20:25:56 +0100 Zog The Undeniable
><[email protected]> wrote:
>
>>The sizes are here, and the 1" ISO size is "Campagnolo" standard:
>>
>>http://www.sheldonbrown.com/gloss_h.html#headset
>
>This is a nice collection of info, but it only gives the headset
>dimensions. It would be even more useful if it also gave the
>dimensions for the mating part on the frame and fork. I think that's
>what the OP wanted to know.
>-
>-----------------------------------------------
> Jim Adney [email protected]
> Madison, WI 53711 USA
>-----------------------------------------------

According to the Barnett Manual, on a 1" ISO headset-

crown race- 26.30–26.40mm
fork column race- 26.45–26.55mm

head tube race- 30.15–30.30mm
head tube- 29.95–30.05mm

So the minimum amount for the proper press fit is .05mm, or about .002
inch, or .001 radially... hmmm.... typical smallest measurement for
calipers? Maybe less would work.

My minimal experience with a fork crown race being sloppy was because
the used bike had been ridden with a misadjusted headset. I ended up
taking down the fork column race on a lathe. A brass pipe was lathed
down to make a shim. Making .001-.002" shim material stay in place for
a circular press fit was beyond me, but with this method I could make
a .010" shim that worked fine.