Bicycle Mechanics - JIS Headsets

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EivlEvo

10-06-09, 03:53 PM

Hey all.

Have a JIS headset in my frame. Looking for a new fork with more clearance.

If I ream the frame to accept an ISO headset, will I still be able to use the stock fork (pending the purchase of a new ISO headset of course)?

Or will I need frame ream, new headset, new fork?

sfclearwater

10-06-09, 07:19 PM

The ISO crown race inner diameter (26.4mm) is smaller than the JIS (27.0mm) crown race inner diameter. You will have a hard time cramming it on the original fork.

As temporary measure, until you get the new fork, you should be able to keep using the original fork with the original JIS crown race in the new ISO headset without too much trouble. Although this could depend on the headset models and dust seals might not fit right.

Alternatively, why ream the frame at all? Just use an ISO crown race on the new fork. Leave the rest of the JIS headset in place...