hokiefyd 

I have a Tange fork that started life with a JIS 27.0mm crown race surface that has been milled to fit an ISO 26.4mm crown race. A 27.0mm crown race fits loosely, as one would expect. There's a very very small amount of play in it. I would like to use this fork in a frame that uses JIS 30.0mm external cups (head tube is about 29.95mm). In general, you can't find a JIS headset with 30.0mm cups that also has an ISO 26.4mm crown race. It seems to be either full ISO (30.2/26.4) or full JIS (30.0/27).

Solution A: buy a full JIS headset and set its 27.0mm crown race onto the Tange fork in some sort of epoxy. I imagine this is generally not the preferred option, though I think the worst that could happen is I find it won't set correctly and there's too much play...and I'm back to square one. I don't see a safety risk with this approach.

Solution B: buy a full JIS headset and then try to find an ISO 26.4mm crown race with a running bearing diameter that's somewhat compatible with the lower cup from my new JIS headset, and then use this ISO crown race on the Tange fork. This seems to be the "safest" option, although one that is potentially the most difficult (in terms of sourcing that one ISO race that I'll need).

Solution C: buy a full ISO headset and have 30.2mm cups pressed into my 29.95mm head tube. I've had this done before on another bike and, honestly, I'm not sure I really like this option. The cups went in (by a bike shop) with significant force and I wouldn't swear that the metal didn't fatigue somewhere. I'm at least as concerned from a safety perspective with this solution as I am with solution A (from the perspective of the head tube fatiguing). Maybe aluminum cups would press in easier than steel ones? I see headsets advertised that appear to use aluminum cups. The ISO headset I used on the other bike had steel cups and went in with a real fight.

I see a lot of questions about using an ISO race on a JIS fork (milling is the typical recommendation). I want to go the other way -- I already have a milled fork and I'm trying to figure out how to get back to JIS with it.

I appreciate ideas and suggestions. Thanks.

HillRider

Another option: Have the headtube of the new frame milled to accept 30.2 mm ISO cups and buy an all-ISO headset.

dedhed

Most Tange threaded headsets (Levin etc) you can buy the crown race separate and they are mix & match

https://www.universalcycles.com/shop...s.php?id=49908

bikemig 

Velo orange also allows you to mix and match. I had to do that on my Melton bike.

hokiefyd 

Thanks -- I didn't know the mix-and-match was available like this. I'm anticipating using a Tange chrome/polished headset, so will look into just buying the ISO crown race separately.