Originally Posted by tedh1951

I'm not quite sure what is going on here - clocking the mouthpiece for best performance goes against all engineering logic IF the machining process always uses the same centre reference. If however, the cup machining and the backbore machining are carried out using a different mounting reference then the centring of the cup compared to the backbore may vary. It seems illogical that any machinist worth his salt would allow such a situation to occur. I'm certainly going to play with my mouthpieces and see if you blokes are pulling my leg, or not. (Thinks: have these blokes finally sucked me into an urban myth that I am unaware of - perhaps serve me right for making light in a serious forum such as TM?)