841020A08 Mercury CYLINDER HEAD ASSEMBLY, Port

If the valve lash requires adjustment several times in a short period of time, excessive wear exists in a different part of the engine. Repair the problem in order to prevent more damage to the engine.Not enough valve lash can be the cause of rapid wear of the camshaft and valve lifters. Not enough valve lash can indicate that the seats for the valves are damaged.Valves become damaged due to the following causes:
The fuel injection nozzles do not operate correctly.
Excessive dirt and oil are present on the filters for the air inlet.
Incorrect fuel settings on the fuel injection pump.
The load capacity of the engine is frequently exceeded.Too much valve lash can cause broken valve stems, springs, and spring retainers. Too much valve lash can be an indication of the following problems:
Worn camshaft and valve lifters
Worn rocker arms
Bent pushrods
Broken socket on the upper end of a pushrod
Loose adjustment screw for the valve lashIf the camshaft and valve lifters show rapid wear, look for fuel in the lubrication oil or dirty lubrication oil as a possible cause.The valve lash is measured between the top of the valve stem and the rocker arm lever.Valve Lash Check
The valve lash setting is for a cold engine.Valve Lash Setting Inlet valve ... 0.35 mm (0.014 inch) Exhaust valve ... 0.35 mm (0.014 inch)If the measurement is not within the acceptable clearance, adjustment is necessary. Refer to "Valve Lash Adjustment".Valve Lash Adjustment
Note: The No. 1 cylinder is at the front of the engine.
Illustration 1 g00323903
Setting the valve lash (1) Adjustment screw (2) Feeler gauge
Accidental engine starting can cause injury or death to personnel.To prevent accidental engine starting, turn the ignition switch to the OFF position, place a do not operate tag at the ignition switch location and disconnect and tape the electrical connection to the stop solenoid that is located on the fuel injection pump.
Remove the valve mechanism cover and perform the following procedure in order to adjust the valve lash:Note: Later engines may require the use of a TORX T27 driver to adjust valve lash.
Rotate the crankshaft in the normal rotation of the engine. When the inlet valve of the No. 4 cylinder has opened and the exhaust valve of the No. 4 cylinder has not completely closed measure the valve lash of the inlet valve and the exhaust valve of No. 1 cylinder. If necessary, make adjustment.
Loosen the valve adjustment screw locknut that is on adjustment screw (1) .
Place the appropriate feeler gauge (2) between the rocker arm and the valve stem. Turn adjustment screw (1) while the valve adjustment screw locknut is being held from turning. Adjust the valve lash until the correct specification is achieved.
After each adjustment, tighten the valve adjustment screw locknut while adjustment screw (1) is being held from turning.
Rotate the crankshaft in the normal rotation of the engine. When the inlet valve of the No. 2 cylinder has opened and the exhaust valve of the No. 2 cylinder has not completely closed measure the valve lash of the inlet valve and the exhaust valve of No. 3 cylinder.If adjustment is necessary, refer to Steps 1.a, 1.b, and 1.c.
Rotate the crankshaft in the normal rotation of the engine. When the inlet valve of the No. 1 cylinder has opened and the exhaust valve of the No. 1 cylinder has not completely closed measure the valve lash of the inlet valve and the exhaust valve of No. 4 cylinder.If adjustment is necessary, refer to Steps 1.a, 1.b, and 1.c.
Rotate the crankshaft in the normal rotation of the engine. When the inlet valve of the No. 3 cylinder has opened and the exhaust valve of the No. 3 cylinder has not completely closed measure the valve lash of the inlet valve and the exhaust valve of No. 2 cylinder.If adjustment is necessary, refer to Steps 1.a, 1.b, and 1.c.