When the engine is running, the plate tappet "203" is unloaded when the cam "184" of the camshaft "185" is directed upward.
The spring "d" presses the compensating element "204" so that it is adjacent to the end face of the valve "195" at the bottom, and at the top the pressure pin "a" presses the plate tappet to the camshaft. In this position, the engine oil can flow into the working volume "c" or flow out of it through small openings "e". As soon as the plate tappet is loaded by the cam of the rotating camshaft, the ball valve "b" closes, and the oil enclosed in the working volume, since it is not compressed, behaves like a solid body. In this way, the length "L" with each revolution of the camshaft adapts to the corresponding changes in the size of the unit in the valve drive.
Distinctive features of hydraulic tappets are a lubrication groove with circulating oil and the absence of adjusting washers.
Note: It is normal for the valve train to make noise when starting the engine. When the engine is stopped, more or less oil is squeezed out of the individual tappet depending on the cam position. This causes noise until the hydraulic tappets are filled with oil again while the engine is running. To ensure the perfect functioning of the hydraulic tappet, a check valve is installed in the cylinder head, which prevents the oil from completely flowing out of the oil grooves when the engine is stopped.
Examination
Hydraulic valve lifters should be checked if noise occurs in the valve train after reaching operating temperature.
Warm up the engine, then let it idle until the fan turns off.
Increase the engine speed to 2500 rpm for 2 minutes.
If the hydraulic lifters are still making noise, stop the engine and remove the cylinder head cover.
Turn the camshaft so that the cams of the cylinder being checked are directed upwards. To do this, shift the gearbox to neutral, tighten the handbrake and turn the crankshaft clockwise using the central bolt securing the belt pulley with a suitable wrench.
Press the plate tappet down with a wooden or plastic wedge. If you feel more than 0.1 mm of free play before the valve moves, replace the plate tappet.
Caution: After installing a new hydraulic tappet, the engine must not be started for approximately 30 minutes, otherwise the valve may hit the piston, causing damage to the piston and/or valve.
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