PX "Cosa" clutch (1995 onwards)

From 1995 onwards the "Cosa" clutch was introduced to PX electric start scooters.

This redesigned clutch, borrowed from the Vespa Cosa, featured 4 cork "friction" plates and 4 steel "plain" plates, again arranged inside the basket in alternating fashion (cork, steel, cork, steel, etc.). Instead of the 6 or 7 large springs located in steel cups inside the basket, the Cosa clutch has 8 small springs fixed to locating pins which are found inside the basket around the perimeter of the central hole.

The clutch is located on the crankshaft by means of a woodruff key and it is secured to the crankshaft itself by means of an M12 x 1.5 nut with "pinched" edges and an extended flat base. The torque wrench setting for this nut is 28.93 - 32.55 lbf ft.

The Cosa Clutch centre nut with pinched edges and extended flat base

The Cosa clutch is easier to "pull" and disengage than the earlier design of clutch and generally provides a smoother gear transition. But this lightness and smoothness come at a cost. The Cosa is notoriously harder to adjust and has a tendency to be a "grabby" clutch with excessive drag. In racing applications, the older design of clutch has tended to be favoured by aftermarket performance parts engineers. Nevertheless, there are performance versions of the Cosa (as for example the enormous Cosa clutch built by the German firm Scooter & Service - a 16-spring version!).