Briefly, the intake cam sprocket is engaged with a matching-sized plate on the end of the intake camshaft. Both the sprocket and the plate are machined with radial grooves, in which sit heavy metal balls. On one face, the radial grooves are straight, while on the other they’re curved. That means that when the metal balls are flung outward by centrifugal forces, the camshaft is rotated by a few degrees in relation to the sprocket. The grooves are shallower at the outer edges and the two mating faces are forced together by a spring, so when revs drop and the camshaft slows down, the balls are pushed back toward the middle, bringing the cam timing back to its initial point.