Camshaft, Lifters and Push Rods: Description and Operation

Oil Path Trough Cam Follower:

Cam Follower Assembly:

HYDRAULIC CAM FOLLOWERS
The valve gear incorporates hydraulic cam followers, which keep the valve clearance within a limited working range of 2.05 mm (0.081 in), between 18.75 and 20.8 mm (0.738-0.819 in) from the camshaft bearing seat to the end of the valve stem.

Each cam follower has two storage chambers and one high-pressure chamber. The opening of the port between the high-pressure chamber and the adjacent storage chamber is controlled by a spring-loaded ball valve. A return spring in the high-pressure chamber acts on the sliding piston, to eliminate any clearance between the cam follower and the cam. At the same time, the high- pressure chamber expands and makes up the oil volume, to compensate for leakage losses through the passage between the piston and the cylinder, occurring at actuating pressure.

Under some conditions, the hydraulic cam followers may give rise to a chattering noise of varying intensity. In most cases, the noise will be short-lived and no remedial action will need to be taken.

For details on the commonest conditions underwhich noise occurs, the likely cause of the noise and preliminary action that may be taken to get rid of the noise refer to Testing and Inspection/Procedures.
Valve