THE WORM TURNS
While Kawasaki’s Bsa-influenced ohv W1 twin of 1966 used a pivoting lever to transmit clutch cable motion to the pushrod in the gearbox mainshaft, their triples and early dohc fours including the Z650 use a ‘worm’ or ‘quick-thread’ mechanism. It consists of inner and outer components with an interlocked coarse thread. When the inner part is rotated by a lever pulled by the clutch cable, the fixed outer part forces it to move axially and push against the rod. It’s a compact and sturdy system, with smooth action as long as the thread is free from dirt and gunge.