Camshaft Lifter Tappet Follower
Overhead Camshaft Lifter Follower (Cutaway Cylinder Head) Step 2 - The lifter provides the automatic adjustment (In older engines, valve lash must be adjusted by hand) which is supplied by oil pressure. When the lifter is forced away from the camshaft by rotation, the oil valve inside the lifter is closed which traps the oil inside the lifter while opening the valve. The follower then transmits the force to the valve stem.
Lifter Oil Passage (Cutaway) Camshaft In Block Step 5 - The alternative design to overhead valve train construction is the in block camshaft, (IBC) this design is traditionally an older design and less efficient than its counterpart due to the added weight of the additional components such as a pushrod and full rocker arm which required a heavier valve spring.
Camshaft In Block (Bottom)