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A hydraulic tappet, also known as a hydraulic valve lifter or hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. Conventional solid valve lifters require regular adjusting to maintain a small clearance between the valve and its rocker or cam follower. This space prevents the parts from ...
With proper analysis, problems relating to valve adjustment, hydraulic tappets, push rods, rocker arms, and above all, valve float, became things of the past without desmodromic drive. Today [ when? ] most automotive engines use overhead cams , driving a flat tappet to achieve the shortest, lightest weight, and most inelastic path from cam to ...
A hydraulic tappet, also known as a "hydraulic valve lifter" and "hydraulic lash adjuster", contains a small hydraulic piston that becomes filled with pressurised engine oil. [4] [11] The piston acts as a hydraulic spring that automatically adjusts the tappet clearance according to the oil pressure. Although the movements of the piston are ...
Various techniques have been used to offset the effect of stiffer springs, such as dual-spring and progressive-sprung valves, roller-tipped tappets, and pneumatic valve springs. Valve float can also be prevented by using lighter valvetrain components. Titanium valves, retainers, and pushrods are commonly used for this purpose. Undercut valves ...
The valve timing of a diesel engine also depends on tappet clearance of the inlet and exhaust valves. If tappet clearance is less, then valve will open early and close late. [2] If tappet clearance is more, then valve will open late and close early. Tappet clearance is measured by an instrument called feeler gauge.
Depending on the design used, the valves are actuated by a rocker arm, finger, or bucket tappet. Overhead valve engines use rocker arms, which are actuated from below indirectly (through the pushrods) by the cam lobes. Overhead camshaft engines use fingers or bucket tappets, which are actuated from above directly by the cam lobes. [3]
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Hydraulic lifters were first put into engines, in mass production, in the 1950's by General Motors. Since then Hyrdraulic Lifters have always been a mainstay in domestic engines. In other parts of the world where smaller engines are utilized the tendency was to stick with direct acting tappets however, again, in the past five to ten years the ...