Bicycle Mechanics - Replacing a 1" threaded headset - JIS or ISO?

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bellweatherman
06-06-08, 03:00 PM
I took an old 1" JIS threaded headset out of an old frame I am rebuilding. I've since thrown away that headset and it's crown race. Can I just install a 1" ISO headset in it's place with a new crown race?

HillRider
06-06-08, 03:15 PM
No, not directly. JIS cups are smaller and the crown race is larger than ISO. An ISO crown race can be fitted to a JIS fork if the fork's crown race seat is milled down to the smaller diameter and ISO cups can be fitted if the headtube is reamed out.
Gonzo Bob
06-06-08, 06:08 PM
You probably won't need to ream out the headtube since ISO cups are only 0.2mm larger than JIS. I had an old ISO headset I started to put into my old Diamondback. I got the cups in fine and then realized that the Diamondback takes a JIS when I tried to get the ISO crown race on.

HillRider
06-06-08, 07:11 PM
You probably won't need to ream out the headtube since ISO cups are only 0.2mm larger than JIS. I had an old ISO headset I started to put into my old Diamondback. I got the cups in fine and then realized that the Diamondback takes a JIS when I tried to get the ISO crown race on.
Yeah, ISO cups can be forced into a JIS headtube without real problems. Headset presses are pretty strong and will overcome the extra resistance with out too much fuss and headtubes are usually pretty maliable. The crown race is a different story and I've seen ISO crown races split when forced onto a JIS fork
bellweatherman
06-07-08, 02:32 PM
Thanks for the advice guys. I'm just going to save myself the hassle and get a 1" JIS headset and new JIS crown.