In the valve-actuating mechanism, cam followers change the rotary motion of the cam-shaft to reciprocating motion. This action opens the valves. Cam followers ride the flat of the cam and are raised, as the cam rotates, by the high side of the cam and lowered by tension from the valve

Figure 4-5.Cam followers.

spring. Three types of cam followers that are used in internal-combustion engines are shown in figure 4-5.

Hydraulic valve lifters (lash adjusters) are used on some engines to avoid the necessity of a clearance otherwise needed in the valve gear to allow for expansion resulting from temperature changes. Hydraulic valve lifters also eliminate the need for manual adjustment to take care of the wear at various points of the valve gear. They may be installed on the rocker arms, valve bridge, or cam follower. Figure 4-6 shows a larger sectional

Figure 4-6.Hydraulic lash adjuster.

view of the hydraulic lash adjuster that is shown in figure 4-7.

Hydraulic lash adjusters may vary in design but generally consist of such basic parts as a cylinder, a piston or plunger, a ball check valve, and a spring. As precision parts, hydraulic valve lifters or adjusters require special care in handling and must be kept exceptionally clean. Abrasive materials must not be allowed to enter a hydraulic lash adjuster if the lash adjuster is to perform its function satisfactorily.