The primary clutch is an advanced form of centrifugal clutch and is often mounted towards the output end with the motor crankshaft. The clutch has two sheave faces; one that is laterally fixed (stationary sheave), and one that can shift out and in to engage the belt (moveable sheave). https://gearbox-cvt19631.blogolize.com/the-gearbox-cvt-diaries-71503888