Swapping out forks on my Schwinn I discovered when removing
the HS crown race of the old forks that it had been shimmed
to provide a snug fit. (Considerate of my LBS to tell me
this when they installed their HS.) A caliper reveals that
the YST's crown race is 27mm while both the original and
replacement forks have 26.4mm crown race seats. The shim
itself appears to improvised from a beer can. Looks like
Stella Artois. Good taste!
Though I wasn't pleased to discover the arrangement, I
confess the crown race fit was quite secure; it took effort
to remove and obviously was pressed on with force. As it
should be. Looks like the LBS wrench was familiar with the
procedure.
The headset is a threadless 1 inch YST HP250A. It has ball
bearings in the upper cup and rollers in the lower. I didn't
want to utilize the shimmed crown race setup with the new
forks - partially because I really don't know how to press
fit the shim/race combination onto the seat without mangling
the delicate shim.
So I reached into the parts box. There I had an old FSA
Duron 1" threaded HS - also of an upper ball/lower roller
configuration. The FSA employs a split collar that slides
over the fork crown race seat. No press required. Two
conical sleeves act as races and sandwich the roller bearing
cage with the lower race sitting atop the split collar.
It mimics the setup of the YST HS, with the exception that
the YST's collar (previously referred to as crown race) is
not split. But despite the collar being press fit onto a
fork's crown race seat, it also forms the base of a conical
race/ roller bearing sandwich like the FSA. (ie the rollers'
lower conical race rests directly atop it.)
Another point: Since the FSA employs a split collar I'm
unsure whether it's specifically designed for a 26.4mm
crown race seat (it initially was installed on such), a
27mm seat or both.
I initially contemplated replacing the lower cup assembly of
the YST HS with that of the FSA. Aesthetically, it's not an
issue that the HS employs cups of different makes. But I do
want the result to be mechanically sound.
But, first I thought to try this: Installing the FSA's split
collar and using it conjunction with the YST's lower bearing
cup assembly - sans it's own press fit collar. I reassembled
the bike and set the HS preload. The bearings aren't
binding, the forks turn freely and there's no play in the
HS. But this isn't exactly a rigorous test of the soundness
of the proposition.
I haven't gone for an extended ride yet. Any comments
before I do.
Thank you Luke