Originally Posted by
xenologer
Nope, that's not how it works. You'll need to remove the threads, and then machine a bevel at the same angle as the sides of the 'nylon washer' (better described as 'compression ring') ?got a lathe? I doubt it, just buy a threadless headset upper.
it's not just about centering the cone, it transfers force from the bearings to the steerer. so its important that the faces match. and get an aluminum or steel compression ring, the nylon ones are cheap and squish and lose adjustment.
Thanks; this is helpful. My challenge is finding a JIS 1" threadless. I've checked Nashbar, Jensen, Chain Reaction, eBay, etc. I seem to come up with the Ritchey Logic, the Miche, and the Sunlite I posted earlier. But, each of these seems to be ISO.
The Origin8 headset that Harris Cyclery sells says it comes with both crown race sizes, so maybe most of these do, or he ones that specify two crown race sizes, at least.
https://www.sheldonbrown.com/harris/...hreadless.html
I guess the best option is to have my bike shop ream out the frame for an ISO headset, and just get an ISO headset that also comes with a 27.0mm crown race (like that Origin8 one)? Interestingly, the picture appears to be of a threaded headset!