I built my C456 with 1 1/8 forks and a reducer head race. All perfect.
When I added the tapered steerer Revs, first ride the headset came very loose and I tightened it, but next ride it was making an odd 'cracking-clunking' noise but there was little or no play in it. I took the HS apart and thought it might have been something to do with the split tapered ring in the O-O headset. I checked it all, and put it back together as tight as possible, and also added a taller spacer above the stem just in case the top cap was grounding on the steerer.
Next ride, after a few miles and some bumps the cracking/knocking noise was back, I cranked the HS down as tight as I dared and it seemed to stop, then it came back again!! No play at all at this point, and I was worried the alloy insets the HS presses into were moving in the frame by now...
So I stripped the HS down again and the tapered ring in the HS was so tightly wedged between the steerer and the bearing I had to pry it out with a screwdriver, as I did so I could hear and feel the crack/creak noise! But no movement anywhere in the assembly.... Deffo the ring causing it...
So after a bit of examining it turns out the headtube on the frame is too short for the taper on the fork steerer! The tapered washer is not fitting between the bearing and the top of the taper on the steerer properly, and as it's not parallel with the taper of the steerer, and that's what's creaking
Crap pic to try and show the problem

Untitled by PeterPoddy, on Flickr
So, I've filed the inside of the tapered washer to a knife edge taper (Almost) itself, to match the steerer, and reduced the flange under the taper you see there to half that height, refitted it all with plenty of grease. In a garage test it seems OK, but another Peaks ride tomorrow will show if I'm right.
Anyway, the only real fix I can think of is a top headset race that's taller to move everything up higher away from the taper, but I'm wondering what might fit instead, it's just a normal top race, right???

