Hydraulic valve lifters

The principle of operation of the hydraulic pusher

Details of the hydraulic valve lifter

The use of hydraulic tappets provides automatic compensation of valve clearances in operation.

Under spring pressure, the plunger and cylinder move away from each other, due to which the gap between the camshaft cam and the valve wire lever is selected. The high pressure chamber is closed by a check valve.

At the moment the camshaft cam hits the end of the pusher, the check valve closes the chamber and the pressure in it increases. The pusher thus works as a rigid body.

At maximum cam lift, it presses on the pusher with force, which leads to a significant increase in pressure in the pusher cavity. A small amount of oil is ejected through the gaps between the cylinder and the plunger, which leads to compression of the hydraulic tappet (maximum by 0.10 mm).


With further rotation of the camshaft, the cam stops pressing on the pusher and the pressure inside the pusher drops. The spring spreads the plunger and cylinder, thereby choosing the gap between the cam and the valve lever. At this point, the check valve opens and some oil from the oil line enters the high pressure chamber. This number depends on the size of the selected gap.

Dismantling of a pusher can be made after removal of a lock ring. However, if the pusher fails to work after a long period of operation, it is recommended to replace the pusher completely.

During operation of hydraulic tappets, the socket in the cylinder head usually wears out and replacement of the head is required.

If there are signs of wear on the surface of the pusher in contact with the camshaft cam, the pusher must be replaced, since grinding the surface leads to a decrease in the total length of the pusher, as a result of which the conditions for adjusting the valve clearance will change.