Originally Posted by
hokiefyd
Should I need to measure the diameter of my head tube, or should any 1" threadless setup work? For 10 bucks, I'll just do this instead of trying to cobble together other parts.
The 1" threadless headset on EBay should work, except if lists a crown race diameter of both 26.4 (ISO) and 27.0 (JIS). Well, it cannot be both. So you have to figure out what your frame and fork dimensions are. Most bike shops will be less than no help here, and their slim 1" headset inventory consists of useless, orphaned JIS units. And they don't know the difference.
And when they try to install your new headset, they'll be mystified when either the new headset cups are loose (diagnosis: you need a new frame), or the immense compressive forces they've had to apply to get the cups in has split your head tube (diagnosis: Wtf??).
So you need to know with absolute certainty if your bike is JIS or ISO...
BTW: your frame and fork may be different (mixed) specs. As may be the headset..
If it was me, I'd leave the bottom headset parts in place, unless it is 'indexed'.