I'm adjusting the threaded headset on my Brompton (if that matters). I read Sheldon Brown's and Park Tool's articles on this topic and followed the recommendations. I adjust the upper race so that there is no play in the headset and handlebars flop to one side when I lift the front wheel holding the frame. The problem is, when I tighten the locknut with a wrench while holding the upper race with another wrench I still have the upper race move slightly. Thus, I get too stiff an adjustment -- handlebars do not flop to one side anymore and I feel the front wheel rotate tighter than it probably should. How do I properly tighten the locknut then?
P.S. For now, I have managed to tighten it somehow, with trial and error and then more trial and error. But still I believe I'm missing something here.