The valve train system in an automotive engine is responsible for the precise control of airflow, fuel delivery, and exhaust gas expulsion into and out of the combustion chamber. The valve train is comprised of multiple components, including the camshaft, rocker arms, pushrods, lifters, and valves, that work together to achieve the proper engine performance.
The camshaft is a long shaft located within the engine block that is responsible for operating the engine valves. It is typically driven by the engine's crankshaft through a timing belt or chain. The camshaft has a series of uniquely shaped lobes, and as the camshaft rotates, the lobes come in contact with the rocker arms.
The rocker arms are mounted on pivots and sit on top of the engine's cylinder head. When the camshaft lobes push the rocker arms, they pivot, and in turn, push down on the pushrods.
The pushrods are slender rods that transmit the force from the rocker arms to the lifters. The lifters are small cylinders that sit on top of the engine's cylinder head and ride on the camshaft lobes. As the pushrods push the lifters, they open and close the engine's valves, allowing air and fuel to enter the combustion chamber and exhaust gases to exit.
During the engine's combustion cycle, the camshaft rotates, and the lobes push the rocker arms, causing the pushrods and lifters to operate the valves. The camshaft's unique lobe shape determines when the valves open and close, and this timing is critical for the engine's proper operation.
Common problems that can occur in the valve train system include worn camshafts or lifters, bent pushrods, and valve spring failure. Timing belts and chains can fail due to overheating, incorrect installation, or prolonged high speed. Oil leaks often lead to valve stem seal wear. Valves can become stuck because of a lack of lubrication, incorrect valve adjustment, or overheating. These issues can lead to reduced engine performance, increased emissions, engine misfires, and even engine damage.
Valve train system repairs can range from simple adjustments to replacing major components such as the camshaft or lifters. Regular maintenance, including oil changes and valve adjustments, can help prolong the valve train system's life and prevent some of the common issues. During a valve adjustment, the mechanic checks and corrects the clearance between the valve stem and the rocker arm or lifter.