It depends on the age, condition, and brand of the vehicle you drive. Due to the popularization of roller follower valve train designs that reduce friction and hydraulic lifters (valve lifters) that help maintain optimal valve clearance, valve adjustment is not needed as often, if at all, in modern vehicles as in older ones.
When applicable, valve clearance specifications and valve adjustment procedures vary significantly by manufacturer. Maintenance schedules for some recent Hyundai engines, for example, require a valve clearance inspection at 60,000 miles; some Hondas call for an inspection at 110,000 miles; some manufacturers advise that valves only be inspected if there is excessive noise; others do not mention valve clearance at all in their maintenance schedules. Your vehicle’s maintenance schedule should be detailed in the owner’s manual, so check it first if you are unsure.
Types of Valves and Operation
Valves resemble inverted, spring-loaded golf tees that are opened by lobes on rotating camshafts, either directly in overhead cam engines or via pushrods acting on rocker arms in overhead valve (pushrod) engines. With prolonged duration and use, the clearances between the lobes or rockers and the valve stems they act upon can become larger. This often leads to a tapping noise or more engine vibration that a driver may not notice for a while, as it increases gradually, but will need adjustment to correct. With exhaust valves, the clearance can become tighter over time as the valves or valve seats wear down, decreasing the clearance, known as lash, between the valves and 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 exhaust valves allow exhaust gases to escape. Too much or too little valve clearance can lead to poor performance or rough idling, as the engine cannot “breathe” normally and operate at its peak efficiency. Too much clearance means the valves will likely tap and, in the long term, damage the valves, camshaft lobes, or rocker arms. If the valve clearance is insufficient, the valves do not close fully, causing excessive heat and the engine will lose power.
How to Check Your Valves (and When to Have Them Repaired)
If your engine produces a tapping noise, it might be time to adjust the valve clearance, although a tapping noise can also be caused by a loose rocker arm or another component; the mechanic won’t know for sure without inspecting the valves. On some engines, valves do not produce noise when there is too much clearance, but valve issues can manifest in other ways. A loss of power can 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 gap between the intake and exhaust valves and their lobes or rockers using thin feeler gauges as shown above. (The camshaft must be in the correct position and each valve must be completely closed for each measurement.) If necessary, adjustment requires installing or replacing shims using special tools, and it is not a quick maintenance item like an oil change, especially on engines with three or four valves per cylinder. Expect to pay at least a few hours of labor at the shop and fees just for the inspection.
Eliminating valve tapping is one benefit of having properly adjusted valves, but the engine will likely become smoother and more responsive. Additionally, proper adjustment can extend the life of the valve train.