LO 9-10 Outline the service procedure used to adjust the clearances of intake and exhaust valves

Performing a Valve Adjustment

As valve seats, faces, and the tip of a valve stem wear, the clearances between the valve stem and the rocker lever change. The camshaft and other valve train parts can wear as well, which changes the timing of valve opening and closing. As this happens, the engine’s ability to move air in and exhaust gases out is altered. The duration of each stroke changes and engine operation deteriorates, with power output dropping, engine brakes not working as effectively, and fuel consumption and emissions increasing. Today’s engines use valve angles and valve train materials that are extremely wear resistant, which means the need to adjust the valves is less frequent than just a few years ago. In fact, adjusting valve lash is a procedure done less frequently than simply checking the valve lash. Today’s valve bridges are universally nonadjustable, and few engines in service use adjustable bridges or crossheads.

To perform a valve adjustment for an in-line six-cylinder engine with a firing sequence of 1-5-3-6-2-4, follow the steps in Skill Drill 9-2. This generic procedure uses the concept of identifying paired cylinders to determine which valves can be adjusted. This procedure is outlined with the assumption that there is no engine compression release brake on the engine.