Views:3 Author:Site Editor Publish Time: 2020-05-20 Origin:Site
When the engine is operating, the valve will expand as the temperature rises. If there is no gap between the valve and its transmission parts in the cold state or the gap is too small, then in the hot state, the heated expansion of the valve and its transmission parts will inevitably cause the valve to close tightly, causing the engine to leak during the compression stroke and the power stroke Gas, so that the power drops, even in severe cases, it is not easy to start. In order to eliminate this phenomenon, when the engine is coldly assembled, a certain gap is left in the valve and its transmission mechanism to compensate for the expansion of the valve after heating. This gap is called the valve gap.
What happens if the exhaust valve clearance is too large or too small
Engine valve phase
The gap of the exhaust valve cannot be adjusted when the intake valve has just opened, because the exhaust valve is not completely closed at this time.
Most people would think that 4-stroke engines, of course, intake, compression, work, and exhaust each occupy 180 °. The intake and exhaust valves are opened and closed at the top and bottom dead centers, and the duration is 180 ° crank angle. But this is not the case. Due to the high engine speed, a travel time is very short. In addition, it takes a process to drive the valve to open by the cam, and the time for the valve to fully open is shorter, so it is difficult to achieve sufficient intake and exhaust exhaust in such a short time. In order to improve the ventilation process and improve the engine performance, the actual engine valve opening and closing is not exactly at the top dead center and bottom dead center of the piston, but appropriate advance and lag to extend the intake and exhaust time. This is the valve phase of the engine.
In actual engine operation, the intake valve is opened before the piston runs to the top dead center of the exhaust stroke, and is closed after the piston runs to the bottom dead center of the intake stroke; the exhaust valve is In the latter part of the power stroke, the piston starts to open before reaching the bottom dead center, and then closes after the piston runs to the top dead center of the exhaust stroke.
Because the intake valve opens before top dead center. The exhaust valve closes after top dead center. This phenomenon occurs when the exhaust valve and the intake valve open simultaneously for a period of time. This phenomenon is called valve overlap. The crank angle during the overlap period is called the valve overlap angle. Because of the valve overlap angle, fresh gas can be used to impact the residual exhaust gas in the combustion chamber, which can make the engine intake air more complete and exhaust more exhaustive, effectively improving the efficiency of the engine.
Therefore, when the intake valve has just opened, the exhaust valve has not been completely closed, and the valve is in the overlapping state at this time, and the intake and exhaust valves are not adjustable.
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