Originally Posted by bigbossman
Yeah, that's the assumption - I have a JIS headset (older Japanese) and a frame that needs an ISO headset.
I must be getting confused, as I thought the cups were the same and the crown race was only different in the ID.
I'm thinking that the best bet might be to buy a new ISO headset. They're not too expensive and I'd hate to ruin the frame over something so trivial. The only part of the old headset that I really want to use is the top race cap that encloses the top bearings, and it should fit ok over an ISO cup.
I agree, I think you'd be better off with an ISO headset. Basically you're getting a "slip fit" (can be installed by hand) with the JIS cups instead of an "interference fit" (must be pressed in), and of course it's supposed to be an interference fit. BTW, here's a link to the Park site, scroll down to the chart showing the different headtube and headset cup dimensions. The ISO standard is referred to as "Euro" on the chart:
http://www.parktool.com/repair/readhowto.asp?id=68