Bicycle Mechanics - fork crown race fit

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engo
10-15-07, 12:17 PM
Hi all,

I am switching the fork on a mid-90s road bike I just bought, replacing the newer carbon fork upgrade with the original steel fork, and I have a question about the proper fit of the fork crown race. I tapped the race off the old fork with persistant, gentle tapping, and it came off fine. The issue is in putting it back on the original steel fork: the bearing slides on with no resistance. It doesn't seem as though there is play in the fit, but it just isn't at all snug (I can move it on and off with my fingers).

Will this be a problem, or is it fine? Should I replace it with one a few micrometers smaller or can I use a piece of aluminum foil as a shim or something?

Thanks,
Neil

Iowegian
10-15-07, 02:47 PM
That's odd since the carbon fork probably uses an ISO (26.4 mm) crown race while an older fork could be JIS (27.0 mm) so I would expect the older fork to have a larger boss not smaller. It's possible that it's just manufacturing tolerances at work but I've never seen a headset race that could be removed by hand unless it was the wrong size.

I'd measure the parts with a micrometer or take it to the LBS (so they can measure it) and go from there. I think locktite makes some sort of stuff that is supposed to tighten up loose press fit parts but I can't remember the details. You could always try aluminum foil but if the crown race seat isn't square your headset may bind up on you.
engo
10-16-07, 12:14 PM
Thanks for the input. I'll get out the micrometer tonight to check out the actual measurements of both forks and the race. It looks as though they are the same (+/- a hair), but that the carbon fork was not manufactured to as close a tolerance as the original Marinoni fork, and the race has been 'stretched'.

I think even if I use a shim, I'll take it the the LBS for proper installation.

Thanks again!
Neil