Hydraulic lifters
Encyclopedia
A Hydraulic Valve Lifter, also known as a hydraulic tappet
or a hydraulic lash
adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. The conventional means of adjusting valve
actuation always requires a small clearance to be left between the valve and its rocker or cam follower
to allow for thermal expansion and wear. The hydraulic lifter was designed to ensure that the valve train always operates with zero clearance, leading to quieter operation and eliminating the need for periodic adjustment of valve clearance.
The hydraulic lifter consists of a hollow expanding piston situated between the camshaft and valve. It is operated either by a rocker mechanism, or in the case of one or more overhead camshafts , directly by the camshaft. The lifter is filled with engine oil intermittently from an oil gallery via a small drilling. When the engine valve is closed, the lifter is free to fill with oil. When the valve is opening and the lifter is being operated by the camshaft, the oil feed is blocked and the lifter acts just as a solid one would, oil being incompressible.
in the early 1930s. Hydraulic lifters were popular on automobile
s designed in the 1980s, but most newer cars have reverted to bucket-and-shim mechanical lifters. Although these do not run as quietly and are not maintenance-free, they are cheaper and rarely need adjustment because the wear caused by operation is spread over a large area.
In certain circumstances, a lifter can "pump up" and create negative valve clearance so that its valve cannot close. Typically this occurs in the most upper rpm range of an engine, and limits the engine's performance. Lifter pump-up is serious, as there may be interference of the valve with the piston or, burned valves may result. In all cases it is important to follow the manufacturer's recommendations for oil viscosity
and quality.
Tappet
A tappet is the noise made by a worn cam follower, however the term is widely used to represent the cam follower itself. In mechanical engineering it is a projection which imparts a linear motion to some other component within an assembly...
or a hydraulic lash
Backlash (engineering)
In mechanical engineering, backlash, sometimes called lash or play, is clearance between mating components, sometimes described as the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established...
adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. The conventional means of adjusting valve
Poppet valve
A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...
actuation always requires a small clearance to be left between the valve and its rocker or cam follower
Cam follower
A cam follower, also known as a track follower, is a specialized type of roller or needle bearing designed to follow cams. Cam followers come in a vast array of different configurations, however the most defining characteristic is how the cam follower mounts to its mating part; stud style cam...
to allow for thermal expansion and wear. The hydraulic lifter was designed to ensure that the valve train always operates with zero clearance, leading to quieter operation and eliminating the need for periodic adjustment of valve clearance.
The hydraulic lifter consists of a hollow expanding piston situated between the camshaft and valve. It is operated either by a rocker mechanism, or in the case of one or more overhead camshafts , directly by the camshaft. The lifter is filled with engine oil intermittently from an oil gallery via a small drilling. When the engine valve is closed, the lifter is free to fill with oil. When the valve is opening and the lifter is being operated by the camshaft, the oil feed is blocked and the lifter acts just as a solid one would, oil being incompressible.
History
The first firm to include hydraulic lifters in its design was Pierce-ArrowPierce-Arrow
Pierce-Arrow was an American automobile manufacturer based in Buffalo, New York, which was active from 1901-1938. Although best known for its expensive luxury cars, Pierce-Arrow also manufactured commercial trucks, fire trucks, camp trailers, motorcycles, and bicycles.-Early history:The forerunner...
in the early 1930s. Hydraulic lifters were popular on automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
s designed in the 1980s, but most newer cars have reverted to bucket-and-shim mechanical lifters. Although these do not run as quietly and are not maintenance-free, they are cheaper and rarely need adjustment because the wear caused by operation is spread over a large area.
Disadvantages
There are a number of potential problems with hydraulic lifters. Frequently, the valvetrain will rattle loudly on startup due to oil draining from the lifters when the vehicle is parked. This is not considered significant provided the noise disappears within a couple of minutes, typically it usually only lasts a second or two. A rattle that does not go away can indicate a blocked oil feed or that one or more of the lifters has collapsed due to wear and is no longer opening its valve fully. The affected lifter should be replaced in the latter situation.In certain circumstances, a lifter can "pump up" and create negative valve clearance so that its valve cannot close. Typically this occurs in the most upper rpm range of an engine, and limits the engine's performance. Lifter pump-up is serious, as there may be interference of the valve with the piston or, burned valves may result. In all cases it is important to follow the manufacturer's recommendations for oil viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
and quality.