What is an Engine Valves: The function of the valve is to help in completing the processes of the intake stroke and exhaust stroke by opening and closing. Each engine cylinder has at least two valves an intake valve and an exhaust valve; the intake valve opens just before the intake stroke begins. This allows air-fuel to enter the cylinder. (air only in diesel engines) The exhaust valve opens just before the exhaust stroke begins so that the burnt gases can exit the cylinder.
The valves are driven by a valve train, there are two basic types of valve train: overhead camshaft bucket with tappets arms and in the block with camshaft push-rods.
The intake valve is usually larger than the exhaust valve because when the intake wall is open the only force moving the air-fuel mixture into the cylinders is atmospheric pressure. When the exhaust valve opens at the exhaust stroke, still high pressure in the engine cylinder lives. A small exhaust valve provides enough room for the high-pressure exhaust gas to exit the cylinder. There is a special coating on the face of the valve. valve face is coated with stellite for severe service. Some valves have a hard alloy tip chrome plated and welded to the stem end. This minimizes Wear on these two areas. The second valve has a hollow stem to reduce weight. Lighter valves reduce the effect of inertia. This increases engine power and responsiveness.
Valve Cooling
The intake valve runs relatively cold.
It only passes the air-fuel mixture but the exhaust wall passes very hot exhaust gases.
The typical temperature pattern for an exhaust wall is the exhaust wall becomes red hot for us with temperatures up to 1600°F, the wall steam being the coldest and the area in between the steam being the hottest.
The wall seat and steam are cooled by the engine cooling system. And this is what the coolant water jacket and the coolant wall pass around the wall seat and the steam is cooled by the engine cooling system. And this coolant passes around the valve seat and valve guide in the water jacket or coolant cylinder head.
Valve Seat
The valve seat is the surface of the machine on which the valve face rests when the valve is closed.
There are two types of valve seats
integral and replaceable
valve: A device that can be opened or closed to allow or stop the flow of a liquid or gas. the word preceding valve usually designates the type of valve needle valve or the function it performs check valve.
valve body: A casting located in the oil pan which contains most of the valve for the hydraulic control system of an automatic transmission.
valve clearance: The clearance in the valve train for when the valve is closed. the lash, or air gap, that allows for expansion due to heat.
valve guide: In the cylinder head a cylinder part or hole in which the valve is assembled and moves up and down
the valve lifter: in an OHV engine the cylinder part that transmits cam lobe movement to the pushrod causing the rocker arm to rock and open the valve may be fixed length or adjustable solid lifters or oil pressure operated hydraulic lifter which are non-adjustable see hydraulic valve lifter
valve overlap: the number of degrees of crankshaft rotation during which the intake and exhaust valve are open at the same time.
valve rotator: A device often installed in place of the valve spring retainer which turns the valve slightly as it opens
the valve spring: The coil spring attached to each valve closes the valve after the cam lobe has rotated past the valve open position.
valve timing: The timing of the opening and closing of the valve in relation t the piston position.
valve train: The series of the part that open and closes the valve by transferring cam lobe movement to the vales.