THE WORM TURNS

Classic Bike (UK) - - WORKSHOP ENGINE IN BITS -

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.

Clutch pushrod is op­er­ated by this sys­tem, seen on mo­tor­cy­cles since the 1910s

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