1 inch carbon steerer (Columbus Minimal forks), full length uncut since the frame is big, a 45mm high steel nitto ahead stem, a 20mm alloy spacer... the top of the steerer is flush with the top of stem (I don't have the few mm theorically needed, my bad, but I don't think my problem comes from there), the alloy lip of the expander nut sits beyond that (approx 2mm high), and on top the @mdcc_tester cap.
I never had problems installing headsets, traditional or ahead, but I can't get this one right (campag record 1 inch)... either it's correctly preloaded, with no play, and when braking at low speed, or applying force on the cockpit, there is friction noise (think Chewbacca) and you can feel some kind of resistance, or, in trying to avoid these symptoms by loosening the preload, I have to suffer some play, an horror on cobbles for instance. There is no happy middle. I've put the bike together last year and never use it (Sunday bike) but going on an audax last weekend with it reminded me of the need to fix that issue for good before I damage things.
What I feel the problem might be is that there is too much of steerer, being 1 Inch diameter it just flexes over that height, and preloading aggravates this. Is it time to slam that stem and cut the height off by the equivalent of the 20mm spacer? The most I could keep of carbon steerer above the stem is 1/2mm because by the time I add the expander bolt's lip , I reach the inner depth of the cap and then I can no longer preload correctly. I guess temporarily fitting the 20mm spacer on top of the stem would give me the beginning of an answer?