The valve is crucial and comprises two kinds of valves, namely, the intake valve and exhaust valve. Its primary purpose is to regulate the opening and closing of the intake and exhaust passages and is made of a head and a rod. While the head is responsible for controlling the intake and exhaust channels, the rod acts as a guide for the valve's movement. The intake valve material is generally alloy steel, while the exhaust valve is crafted using heat-resistant alloy steel. The reason behind using heat-resistant alloy steel is that the exhaust valve's head comes in direct contact with the combustion gas and, therefore, requires a tougher material to prevent any damage.
To make sure that the valve head and valve seat fit tightly and allow for efficient heat conduction, a grinding process is used to create a tapered joint surface between them. The angle formed between the cone surface and the top plane is known as the valve cone angle, with commonly used angles of 30° and 45°. The valve stem serves as a guide for the valve's movement, and typically features grooves on its end to accommodate tapered cleats.
When it comes to the internal components of an engine, the valve seat is an essential part. It is responsible for sealing the valve and maintaining proper compression. The valve seat is a circular hole that is directly processed on the cylinder block or cover, depending on the type of valve system used. It works in cooperation with the valve to create a tight seal that prevents leakage or loss of pressure. To enhance the wear resistance of some valve seats, seat rings can be crafted from alloy cast iron and embedded on the cylinder block or cylinder head. Regardless of its design, the valve seat is a critical component that must function effectively for optimal engine performance.
The valve guide is an essential component of the engine as it is responsible for guiding the valve in its correct axial movement. It also indirectly transfers the heat from the valve stem to the water jacket. To facilitate repair and replacement, valve guides are manufactured separately and pressed into the cylinder block or cylinder head. During installation, it is crucial to ensure a certain level of interference and pressing depth to guarantee optimal heat transfer.
One of the crucial components of the valve mechanism is the valve spring. Its primary function is to maintain a tight seal between the valve and valve seat. Additionally, it slows down and counters the inertial forces created by the valve and other transmission parts, preventing damage to the valve mechanism during normal operations.
A valve lifter is responsible for transmitting the pushing motion from the cam to the valve or push rod in order to control the valve's opening and closing. This component comes in either a side type or overhead type, and it plays a critical role in ensuring optimal engine performance. Without it, the proper timing of the valve's movements may not be achieved, leading to a decrease in engine power and efficiency. Therefore, it is important to maintain the valve lifter to ensure that the engine runs smoothly.
The push rod plays a significant role in the gas distribution mechanism of the overhead valve type. It transmits the tappet's movement to the rocker arm. This straight rod is typically made of hollow steel pipe with dissimilarly shaped ends, which are welded at either end. The upper end is concave spherical, accommodating the ball head of the adjusting screw on the rocker arm. Meanwhile, the lower end is a ball head for insertion into the jig that contains concave ball bearings for rods.
The valve rocker arm plays a crucial role in the engine's operation by altering the movement of the tappet to the valve. This mechanism consists of a dual-armed lever with varying arm lengths and a circular hole in the middle. The long arm connects to the valve's tail with an arc-shaped working surface while the short arm has screw holes for adjustment screws and lock nuts to regulate the valve clearance. The rocker arm bearing, which contains a bronze bushing, is positioned in the middle area.
The rocker arm shaft is a circular and hollow component that is fitted onto the cylinder head by various supports. The shaft allows for the rocker arm to be positioned on it, and this arm can then move in a circular motion along the shaft. The internal hole of the shaft is linked to the main oil passage to provide the lubricating oil that the valve mechanism requires.
The camshaft plays a crucial role in regulating the timing of each cylinder valve opening and closing. In addition, it drives various accessories like the oil pump, gasoline pump, and distributor. Consisting of an intake cam, exhaust cam, journal, gears that power the distributor and oil pump, and an eccentric wheel that powers the rocker arm of the petrol pump, the camshaft operates as a single unit. Overall, this component significantly contributes to the performance and efficiency of the engine.
The camshaft in an engine is typically powered by a pair of timing gears connected to the crankshaft. These timing gears consist of a pinion gear, called the crankshaft timing gear, located at the front of the crankshaft, and a larger gear, known as the camshaft timing gear, mounted on the camshaft's front end. The ratio of these gears is set at 2:1, meaning that for every two rotations of the crankshaft, the camshaft rotates once. This ensures that the engine's valves open and close at precisely the right time.