Hydraulic tappet

The hydraulic lifter, situated between the camshaft and each valve, is a hollow steel cylinder encasing an internal piston.

As the camshaft lobe enters the lift phase of its travel, it compresses the lifter piston, and a valve shuts the oil inlet.

Frequently, the valvetrain will rattle loudly on startup due to oil draining from the lifters when the vehicle is parked.

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.

A number of subcompact car manufacturers prefer solid valve lifters due to lower design and production cost rather than hydraulic tappets.

This has negative impact, especially on the engine camshaft and valves due to excessive wear if the clearance setting is not working correctly.

Used hydraulic lifters should be drained of oil before installation, to prevent them from holding open the valves on startup and potentially causing damage to the valve-train/pistons.