Hydraulic Tappets

Valve actuation with hydraulic tappet: oil under high pressure is shown in red. Light red indicates the amount of oil not required for valve actuation.

1 – camshaft cam;
2 – oil reservoir;
3 – check valve;
4 – oil inflow;
5 – high-pressure chamber;
6 – valve stem;
7 – compression spring;
8 – cylinder;
9 – piston;
10 – hydraulic tappet.

The hydraulic bucket tappets mentioned above incorporate hydraulic valve clearance adjustment. As a result, the valve clearance checks previously required are no longer necessary: the valve train operates without clearance, and the closed valves still seat firmly on the valve seat, ensuring perfect sealing.

Note: After a long period of standing, an engine with hydraulic tappets may produce loud knocking noises on initial start-up. This occurs when all oil has drained out of the hydraulic tappets, creating clearance in the valve train again. There is no need for concern: after a short time the noise stops and the valve train operates quietly again. If one of the hydraulic tappets continues to knock for an extended period even with the engine warm, it must be checked.