Valve Timing Unit
The valve timing unit turns the intake camshaft relative to the primary chain to advance or retard the timing.
The unit consists of a body and sprocket assembly separated from an inner sleeve by a ring piston and two helical ring gears; the inner sleeve is bolted to the camshaft.
The two helical ring gears are part of the cylindrical extension of the piston, one gear on the outer bore (meshing with the helical gear which is on the inner bore of the body and sprocket assembly) and one on the inner bore (meshing with the inner sleeve).
As engine oil pressure moves the piston in the advance direction (to the right on the illustration) the helical ring gear on the outer bore of the piston causes the whole piston assembly to turn to the right as well as moving to the right. In the same way, the movement of the piston to the right, combined with the rotation caused by the outer helical gear assembly, causes the inner sleeve and hence the camshaft to rotate to the right in the advanced direction. The procedure is identical, but in the opposite direction for retarding the timing.
A light bias spring in the retard direction is provided along with anti-backlash springs.