Proper valve lash adjustment is critical for proper engine performance. As an engine runs, the valves open and close to admit air and fuel, and release exhaust. While the valves are closed, they transfer excess heat to the valve seat, thereby maintaining an acceptable operating temperature. If the valves are adjusted too tight, they will not stay closed long enough or may not close at all, and could overheat or burn. If the valves are adjusted too loose, a distinct tapping noise is heard as the rocker arms beat on the valve tips, causing premature wear. Also, too loose an adjustment decreases the distance the valve opens, thereby reducing the amount of air/fuel admitted, and/or the amount of exhaust released, causing a lack of engine power.
To properly adjust the valves, follow the appropriate adjustment procedure below. Insert the proper size feeler gauge between the valve tip and the rocker arm. A slight drag should be felt. If the gauge will not fit, the valve is too tight. Loosen the locknut, then loosen the adjusting screw until the feeler gauge can be inserted. If you cannot feel a slight drag on the feeler gauge, the valve is too loose. Loosen the locknut, then tighten the adjuster until a slight drag is felt. Tighten the locknut while holding the adjuster, then recheck the clearance.
If the engine is equipped with a rear window in the timing belt cover, use Procedure A. If there is no rear window in the cover, use Procedure B.PROCEDURE A
- Rotate the crankshaft clockwise and align the number one piston TDC mark with the notch in the FRONT cover window. Remember, #1 piston is at the flywheel end.
- Rotate the crankshaft clockwise until the first mark appears in the REAR cover window. Align that mark with the cover notch. Loosen the locknut and adjust the #2 intake and #4 exhaust valves to give a clearance of 0.004-0.008 in. for intakes and 0.008-0.010 in. for exhaust. Repeat the procedure as follows:
A special tool is needed for this procedure.
- Remove the distributor cap and rotor.
- Rotate the crankshaft clockwise and align the #1 piston TDC mark with the notch in the timing cover window.
- Position Alignment Rotor Ms.1774 or equivalent tool on the distributor shaft. Position flexible pointer Mot.591 or equivalent tool on the #10 head bolt (nearest the distributor on the left).
- Align the pointer with the TDC index (hole) on the alignment rotor.
- Rotate the crankshaft clockwise two complete turns and re-align the pointer with the TDC index.
- Rotate the crankshaft, slowly, until the #1 index on the alignment rotor is aligned with the pointer. Loosen the locknut and adjust the #2 intake and #4 exhaust valves to provide a clearance of 0.004-0.006 in. for intakes and .008-.010 in. for exhausts. Tighten the locknuts. Rotate the crankshaft to each cylinder number in turn and adjust the valves as follows: