Engine valve lash should be adjusted at the first oil change on a new engine. On Cat® Marine Engines, the first oil change is typically recommended at 250, 500 or 1000 hours.
A valve lash adjustment is critical because the valves of a diesel engine play a key role in the combustion process. Specifically, the intake valves control the flow of air entering the cylinder, while the exhaust valve controls the flow of exhaust gases exiting the cylinder. Both inlet and exhaust valves must close and seal completely during the combustion process.
Technically, the valve itself is not adjusted, but rather the valve mechanism, i.e., the lifter, push rod and rocker arm assembly. The valve mechanism is adjusted to provide a specific lash (or looseness) necessary to regulate the opening and closing of the valve. If the lash is too loose, the opening and closing of the valve becomes very abrupt which will eventually lead to damage to the valve and/or valve mechanism. If the lash is too tight, the valve cannot close and seal properly in the cylinder head and exhaust gases will leak past the valve. With incorrect lash adjustment, the engine may not operate at full power, fuel consumption may be high and the exhaust smoke and exhaust temperature may be excessive. If left uncorrected for an extended period of time, a catastrophic failure of the valve and engine is likely to occur.
Valve lash adjustment is a relatively uncomplicated procedure.Valve lash should be checked and adjusted as needed as a normal maintenance process every 1,000 to 3,000 hours after the initial adjustment. Consult your Operation and Maintenance Guide for the correct interval and procedure to adjust the valve lash for your engine.