Does your engine need a valve adjustment? It depends on the age, condition and brand of vehicle you’re driving. Due to the popularization of roller-follower valve train designs that reduce friction and hydraulic tappets (valve lifters) that help maintain optimal valve clearance, valve adjustment isn’t necessary as frequently, if at all, in modern vehicles as in older ones.
Where relevant, valve clearance specifications and valve adjustment procedures vary widely among manufacturers. The maintenance schedules for some recent Hyundai engines, for example, call for a valve clearance inspection at 60,000 miles; some Hondas call for an inspection at 110,000 miles; some manufacturers advise valves should be inspected only if there is excessive valve noise; others don’t mention valve clearance in their maintenance schedules at all. Your vehicle’s maintenance schedule should be detailed in the owner’s manual, so check there first if you’re not sure.
Types of Valves and How They Work
Valves look like spring-tensioned inverted golf tees that are opened by lobes on rotating camshafts, either directly in overhead-cam engines or by means of pushrods acting on rocker arms in overhead-valve (pushrod) engines. With extended time and use, the clearances between the lobes or rocker arms and the valve stems they act on can become greater. That often leads to a clattering noise or more engine vibration that a driver might not notice for quite a while, because it increases gradually, but which will be necessary to adjust in order to correct. With exhaust valves, the clearance can become tighter over time as the valves or valve seats wear down, diminishing the clearance, known as the lash, between the valves and the valve train components.
Intake valves open and close to let the air-fuel mixture (or just air in some modern engines) enter the cylinders, and the exhaust valves allow exhaust gases to escape. Too much or too little valve clearance can result in poor performance or a rough idle because the engine can’t “breathe” normally and operate at peak efficiency. Too much clearance means the valves will likely clatter and, over the long term, cause damage to the valves, camshaft lobes or rocker arms. If there’s too little valve clearance, the valves won’t fully close, causing excessive heat, and the engine will lose power.
How to Check Your Valves (and When to Get Them Fixed)
If your engine generates a loud clatter, it could be time for a valve clearance adjustment, though a tapping noise could also be caused by a loose rocker arm or some other component; the mechanic won’t know for sure without inspecting the valves. On some engines, the valves don’t generate noise when there’s too much clearance, but valve issues may manifest in other ways. Loss of power could be a sign of a weak or broken valve spring, for example.
Checking valve clearance requires removing the valve cover (or two valve covers on V-type engines) and measuring the space between both intake and exhaust valves and their lobes or rocker arms using thin feeler gauges as pictured above. (The camshaft must be in the proper position and each valve fully closed for each measurement.) If necessary, adjustment requires installing or replacing shims using special tools, and it isn’t a quick in-and-out maintenance item like an oil change, especially on engines that have three or four valves per cylinder. Plan on paying for at least a few hours of labor at the shop and a charge just for the inspection.
Eliminating valve clatter is one benefit of having properly adjusted valves, but the engine will also likely become smoother and more responsive. In addition, proper adjustment can extend the life of the valve train.
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