Resetting the clearance between the mechanism that opens the valves and the tops of the valve stems, also referred to as adjusting tappets, is accomplished by fitting shims of specific size into the gaps. This is a very precise project that should be handled by a professional mechanic unless the car owner has access to specific tools to accurately measure the gap.
Adjusting tappets only requires a few steps.
Step 1: Schedule your checks
Checking the measurements of the valve clearances should be a part of regular vehicle maintenance. In order to do this effectively, the car owner must understand the firing order of the cylinders in the engine, which rockers or cams operate the valves, and which valves are inlet and which are exhaust. It is also important to determine if the valves should be checked when the engine is "hot," which means it has been turned on, allowed to warm up, and then turned off, or "cold," which means it has not been on in at least 6 hours.
Step 2: Check your clearances
Clearance is measured using a device called a feeler blade. This blade should fit firmly into the clearance. If the blade will not go in or there is enough space that it feels loose within the gap, the tappets should be adjusted.
Step 3: Adjust the tappets
Adjust the tappets by removing the rocker or camshaft and using the adjuster screw to widen the clearance or a shim to lessen the space. Carefully mark or organize each piece as it is removed to ensure they are returned to the appropriate place.