With extended time and use, the clearances between the lobes or rocker arms and the valve stems they act on can become greater.

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. Your vehicle’s maintenance schedule should be detailed in the owner’s manual, so check there first if you’re not sure. 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.

Where relevant, valve clearance specifications and valve adjustment procedures vary widely among manufacturers. Related: Are There Any Mechanical Benefits to Cleaning an Engine?

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. Does your engine need a valve adjustment? It depends on the age, condition and brand of vehicle you’re driving.

Cummins 350 big cam valve adjustment