What is the principle of the engine valve train?
2 Answers
The principle of the engine valve train is: according to the working cycle and ignition sequence requirements of each cylinder of the engine, it opens and closes the intake and exhaust valves of each cylinder on time, draws fresh air into the cylinder, and exhausts the burned gas from the cylinder. The engine valve train mostly adopts overhead valves, which are divided into lower-mounted, mid-mounted, and upper-mounted types based on the position of the camshaft. The engine valve train consists of the valve drive group and the valve group. The valve drive group includes the crankshaft timing gear, camshaft timing gear, camshaft, tappet, push rod, rocker arm, valve clearance adjustment screw and lock nut, and rocker arm shaft. The valve group includes the valve, valve guide, valve spring, valve spring seat, valve oil seal, valve seat, etc.
The valve train of an engine is like its respiratory system, a part I frequently deal with when repairing vehicles. Simply put, it's the control mechanism that allows air to enter the cylinders for combustion and then expels the exhaust gases. The core principle relies on the coordinated operation of the camshaft and crankshaft: as the camshaft rotates, its cams push the rocker arms or lifters to open and close the valves; meanwhile, the crankshaft's rotation drives the pistons up and down. These movements must be synchronized to ensure the intake valves open as the pistons descend, drawing in the air-fuel mixture, and the exhaust valves open as the pistons ascend to expel the exhaust gases. If the timing is off—due to worn cams or a loose timing belt, for example—the engine may lose power, consume more fuel, or vibrate excessively. During routine maintenance, I always check valve clearance adjustments and the condition of the timing chain, as looseness can increase noise or even damage the pistons. To extend component lifespan, I recommend regular oil changes to maintain lubrication and prevent carbon buildup from clogging and affecting performance. These details are fundamental in auto repair; without understanding them, drivers may notice sluggish acceleration.
