The lifter is the link between the camshaft and the pushrod. Because metal expands when it is heated, the link needs to be adjustable. The terms "hydraulic" and "solid" refer to the way the lifter handles this need for adjustment.
Hydraulic Lifters
Hydraulic Lifters automatically adjust. They have a spring-loaded plunger inside. As the engine runs, the body of the lifter fills with oil. The spring and oil allow the plunger to move up and down as needed.
A hydraulic valvetrain is quieter and basically maintenance-free. However, it needs to have a certain amount of preload set when installed.
- Follow this link to learn How to Set Preload.
Solid Lifters
Solid Lifters (aka mechanical) are exactly what the name implies. They are solid pieces of metal between the cam lobe and pushrod. This type of valvetrain needs gaps between components to allow for thermal expansion. These gaps are known as lash.
A valvetrain with solid lifters is noisier and requires adjustment to maintain proper lash. Valve lash is set by adjusting the rocker arm.
- Follow this link to learn How to Set Valve Lash.