Heat produced in the engine causes internal engine components to expand and contract. As the engine heats up, proper valve clearance is essential for optimal performance.
Engines are made of many different materials and metals. Each material expands at a different rate and each engine component is subjected to different levels of heat. Manufacturers design engines to have space between components so that the various components can rotate and function.
To avoid premature wear of internal engine components, it is critical to maintain correct valve clearance. Incorrect clearances can cause the engine’s intake and exhaust valves to fail prematurely, which can lead to engine idle and drivability problems, as well as excess pollution.
The recommended interval for checking valve clearance varies among manufacturers. To check and adjust the valve clearances, the valve cover is removed, the engine is manually rotated, and each valve clearance is measured and adjusted as required.
Mechanics' Corner: More Technical Detail
To ensure longevity and proper operation, the engine valves require a specific amount of clearance (sometimes referred to as "lash"). Extremes of insufficient or a lack of clearance will cause a valve to run hot and leak. A valve that is extremely loose with excessive clearance can suffer from mechanical wear and be noisy. Either insufficient or excessive clearance can cause poor engine performance or failure.
Valve clearance adjustment can be a regular maintenance procedure. On most modern vehicles, however, the proper adjustments are maintained automatically through the design of the valve train (specifically the hydraulic lifter).
The purpose of a valve adjustment is to bring the clearance between the tip of valve stem and the camshaft lobe or rocker arm back in to the specified clearance that was determined by the design engineer. As the camshaft rotates, it pushes on the valve stem either directly or by using a lever such as a rocker arm, to open the valves inside the combustion chambers at the proper time. The valves are closed automatically by the valve springs.
If the valve clearance is too small, the valves will never fully close when they should be doing so and this will eventually burn part of the valve surface off and cause a constantly misfiring engine. If the valves are too tight, the vehicle may also exhibit rough running characteristics either cold, hot or all the time. If the valve clearances get too loose, this will lead to a noisy running engine and will eventually damage the camshaft lobes, rocker arms ( if equipped ) and the tips of the valves themselves.