If cam "184" of camshaft "185" points upward, then disc valve "203" is unloaded.
The spring "d" of the tappet expands the compensator "204" in such a way that it fits below the valve stem "195" and above it presses the rod "a" to the plate "203". In this position, the engine oil cannot penetrate into the space "c" and cannot flow out of it. As soon as the camshaft cam presses on the plate during rotation, the valve "b" closes and the oil inside acts as a solid body, since the eye is practically not compressed. The length "L" changes during the operation of the mechanism, compensating for the wear of the parts.
External signs of a hydraulic tappet are the presence of oil grooves and the absence of adjusting washers. Hydraulic tappets cannot be repaired.
Note: It is normal for the valve timing to make noise when starting the engine. When the engine is not running, some oil is squeezed out of the tappet depending on the cam position. This causes noise when starting the engine, which continues until the hydraulic tappets are filled with oil again. Depending on the circumstances, this may continue until the engine reaches its operating temperature. To ensure reliable operation of the hydraulic tappets, there is a partition in the cylinder head that prevents the oil from draining completely when the engine is not running.
Examination
The hydraulic tappets should be checked if the noise in the operation of the vibratory tappet mechanism does not stop when the engine reaches its operating temperature.
Start and warm up the engine. Then stop it and let it idle for as long as the fan remains on.
Increase the speed to 2500 rpm for 2 minutes.
If the noise in the tappets does not stop, stop the engine and remove the cylinder head cover.
Turn the camshaft so that the cam nose of the tappet being tested is in the upper position. Set the gearbox to idle. Engage the handbrake. Turn the crankshaft clockwise by the central bolt.
Press the tappet down with a wooden or plastic wedge. If the tappet moves more than 0.61 mm before the valve starts to move, replace the hydraulic tappet
Caution: After installing a new hydraulic tappet, do not start the engine for 30 minutes. Otherwise, the valve may collide with the piston, which may cause damage to them.