A THREAD ON THREADS

Paul Hague’s article on screw threads in RC205 was most enjoyable. If ever there was an engineering minefield, it was threads. Should anyone want to delve a little deeper, there is a small book called Drills, Taps and

Dies by Tubal Cain. It only costs about £7 and has lists of all the common and not-socommon threads along with their dimensions and loads of other info.

I agree with Paul on using the correct spanners, but once again there are traps for the unwary. Take the cylinder base nuts on Triumph twins, for example. Here, when the threads were Americanised, the hexagon went from ¼” Whitworth to ½” A/F. Problem was that the old spanner appeared to fit the nuts, but then chewed up the hexagons when you tightened them.

Regarding the clunking on engaging gear mentioned elsewhere, my experience seems to be the opposite of your correspondents. In the 1960s, Triumphs had the reputation for a sticking clutch, which necessitated freeing it off before kicking up. The blame was usually put down to having too thick an oil in the primary chaincase; it needed to be SAE20. Provided these rules were obeyed, I found gear changes were then clunk-free. Compare this with modern machines I have owned, including Honda, BMW, Yamaha among others where first gear engagements always result in a massive clunk. Is this what they mean by progress?

Thanks for a great magazine.

Nick Steel, member 9946

If you want to delight in a truly clonky gearbox, ride a Harley! It really does sound like the earth is moving beneath you. Frank W