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@A_EF
Having difficulty sourcing a JIS 1″ threaded headset. Possible to get on import but many are just regular ISO headsets with 30.2mm cups (instead of 30mm) with the crown race swapped for the JIS 27mm size (to replace the ISO 26mm). eg here
Couple of Q's if anyone can offer any advice? I have a couple of old 27mm crown races already so could I just get the regular ISO headset (available easily in this country and at a reasonable price) and swap the 26.4mm crown race that comes with it for one of my own 27mm ones? Will the slightly wider JIS crown race sit ok with the bearings of the ISO headset? I assume the extra 0.6mm is in the hole and doesn't affect the outside diameter of the race?
If the above works has anyone had any experience of fitting a 30.2mm ISO headset cup into a head tube that is meant to have a 30mm JIS cup? Any warnings? Will I trash / crack the frame? I'm thinking of freezing the cups before fitting them to make this easier.
Its on a very old steel Dawes frame that is slightly worn anyway on the head tube anyway so might have wider tolerance already. I expected it to be standard ISO fitting but looks like it's JIS (which I've found out is likley because of it's age). Luckily the ISO Tange Levin I got for it fitted another bike.
I'm aware I could get the head tube / fork milled but would rather avoid if if possible and go the easy route of getting a regular ISO headset with my own crown race if possible.
Anone got any advice or had experience of this?