Lifters in an engine are cylindrical components that sit between the camshaft and the valves, playing a crucial role in opening and closing the intake and exhaust valves. As the camshaft rotates, its lobes push on the lifters, which then actuate the valves either directly or indirectly, depending on the engine design
. There are two main types of lifters:
- Hydraulic lifters: These use pressurized engine oil inside the lifter to automatically adjust valve clearance (valve lash), reducing noise and maintenance. When the camshaft presses down, oil pressure locks the valve open; when released, the valve closes smoothly. Hydraulic lifters are common in most modern engines but require precise operation and can fail if oil pressure is inadequate or excessive
- Mechanical (solid) lifters: These are solid metal cylinders that require manual adjustment of valve lash. They are simpler, cheaper, and preferred in some performance or economy engines due to their reliability at high RPMs. Mechanical lifters come as flat tappets or roller lifters, the latter having a small roller to reduce friction and noise
In pushrod (overhead valve) engines, lifters push on pushrods that move rocker arms to open valves, while in overhead cam (OHC) engines, lifters may push directly on the valve or valve tappet
. Advanced lifter designs are also used in variable-displacement engines, where special collapsible hydraulic lifters deactivate valves in unused cylinders to improve fuel economy. This is controlled by the engine computer via oil pressure
. In summary, lifters transfer the camshaft's motion to the valves, ensuring proper timing and operation of the engine's air intake and exhaust cycles, which is vital for engine performance and efficiency
