<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2014) (Learn how and when to remove this template message) </Td> </Tr> <P> 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 . 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 binding as they expand with the engine's heat, but can also lead to noisy operation and increased wear as the parts rattle against one another until they reach operating temperature . The hydraulic lifter was designed to compensate for this small tolerance, allowing the valve train to operate with zero clearance--leading to quieter operation, longer engine life, and eliminating the need for periodic adjustment of valve clearance . </P> <P> The hydraulic lifter, situated between the camshaft and each engine's valve, is a hollow steel cylinder encasing an internal piston . This piston is held at the outer limit of its travel with a strong spring . The lobed camshaft rhythmically presses against the lifter, which transmits the motion to the engine valve one of two ways: </P> <Ol> <Li> through a pushrod which actuates the valve via a rocker mechanism; or </Li> <Li> in the case of overhead camshafts, via direct contact with the valve stem or rocker arm . </Li> </Ol>

Where are the lifters located in an engine