The ability to overtighten a headset and not know it (because the leverage the bars have over the bearings) is why when I teach how to adjust a headset I start with the bearings set too loose. Then you tighten them a bit at a time untill the slop (felt with the front brake locked and rocking the bike for and aft) is gone. This actually is the best way for all the other adjustabler bearings too. Loose to just tight enough, to remove the looseness. Oh, and with a headset the adjustment should be checked at a few different steering angles to check for a binding situation (if there's a bent steerer or non parallel bearing seats). Andy.