At the top of the cylinder head is the camshaft. By means of eccentric cams, depending on the position of the pistons of the cylinders, the shaft opens and closes the valves, thus controlling the gas distribution. The camshaft is driven by a toothed belt from the crankshaft.
The camshaft does not directly act on the valves, but indirectly, through poppets (see illustration 7.0).
The poppet pusher is an inverted and put on the valve stem cup. The poppet tappets are equipped with hydraulic compensators, so there is no need to adjust the valve clearance.
Attention! A fairly strong knock in the engine that appears immediately after starting may be the result of the operation of hydraulic pushers. This phenomenon may occur after starting the engine of a car that has not been used for a long time. This occurs as a result of oil leakage from the hydraulic tappets, which in turn leads to the formation of play in the valve drive. In this case, there is no reason for concern. After a while, the engine noise will disappear. But if one of the poppet pushers knocks after some time, including when the engine is warm, then this is a reason to check the valve.
When the valve is in the closed position, oil from the engine lubrication line flows through the groove into the poppet. After passing through the pusher check valve, the oil fills the high pressure chamber, which is currently depressurized. Simultaneously with this process, the pressure spring firmly presses the poppet pusher against the camshaft cam. When the camshaft rotates, its eccentric cam presses on the poppet pusher, thus creating excess pressure in the high pressure chamber. The non-return valve closes the hole through which the oil enters, ensuring that the amount of oil supplied is retained. And since the oil is not compressible, a rigid barrier arises between the poppet pusher and the cylinder and the valve is pressed down by the pressure of the cam.
After the valve is closed, as a result of oil leakage, a slight valve clearance is formed, which is compensated by a pressure spring that pushes the poppet upwards. After opening the check valve, oil begins to flow into the freed space in the high-pressure chamber again and the cycle repeats.
The camshaft cams do not touch the poppets in their center, but slightly to the side. This leads to the fact that each time the cam is pressed, the valve moves slightly around its axis. This avoids uneven impact on the valves and their loose fit.
A gasket is installed between the cylinder block and the cylinder head to ensure tightness and prevent mixing of coolant and engine oil. The gasket is resistant to high temperatures and pressure drops.
Gaskets of different thicknesses are installed on diesel engines. The thickness of the gasket depends on the size of the protrusion of the pistons.
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