 The rockers or cam followers sometimes incorporate a mechanism to adjust the valve lash through manual adjustment, but most modern auto engines have hydraulic lifters, eliminating the need to adjust the valve lash at regular intervals as the valvetrain wears, in particular the valves and valve seats in the combustion chamber.Sliding friction between the surface of the cam and the cam follower which rides upon it can be considerable.In order to reduce wear at this point, the cam and follower are both surface hardened, and modern lubricant motor oils contain additives specifically to reduce sliding friction.