GM Corvette 1963-1982 Repair Guide

Valve Lash

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ADJUSTMENT



See Figures 1 and 2

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Fig. Fig. 1: Valve lash adjustment on a hydraulic lifter engine



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Fig. Fig. 2: Adjusting the solid valve lifters

Engines equipped with hydraulic lifters VERY rarely need adjustment of the valve lash. If the vehicle runs well and there is no audible "clicking" in the valvetrain, leave it alone. This is because removal of the valve covers on vehicles equipped with air conditioning, various emission controls, cruise control, etc., can be a major project in itself.

On air conditioned models, the A/C compressor must be moved out of the way to gain access to one of the valve covers. Do not disconnect the refrigerant lines to move the compressor. After the cover is removed, either move the compressor to retighten the belt or remove the belt completely so that it will not tangle while the engine is running.

On early models equipped with fuel injection, removal of the left valve cover requires removal of the air cleaner hose, air meter adaptor, and pyrometer housing.

If wiring is attached to metal clips on the valve cover, carefully bend each clip to free the wire from the valve cover. If corrugated plastic tubing containing wiring is attached to the valve cover with plastic clips, the clips can be undone by gently twisting the upper part of the clip while holding the lower section. If the clip must be removed, press the lowermost arms of the clips together with needle nose pliers and push upward.

If the vehicle uses a PCV valve pressed into the valve cover grommet, pull the valve from the grommet and remove the valve from the hose. Plug the hose with an old bolt to prevent a vacuum leak. Models having a hose running from the air cleaner to the exhaust manifold require removal of the air cleaner assembly and the hose. Plug any vacuum lines which must be disconnected.

Should it be necessary to remove additional components to gain access to the valve covers, note the wire and/or vacuum hose connection locations and sizes of the bolts which retain the component(s).

  1. Purchase oil stopper clips for the rocker arms. These are available at most auto parts stores. These clips are installed either over (metal style) or in (plastic style) the rocker arm oiling hole located at the pushrod end of the rocker arm. If these clips are not installed, both you and your Corvette will become oil soaked when the engine is started.
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  3. Start the engine and allow it to reach normal operating temperature.
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  5. Remove the valve covers. If you have only 8 oil stopper clips, remove only one valve cover and adjust the valves. Then adjust the valves on the other side after the first cover has been reinstalled.
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  7. Start the engine and allow it to idle.
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  9. FOR HYDRAULIC LIFTER ENGINES: Slowly loosen the rocker arm nut until the rocker arm starts to clatter. Tighten the nut (clockwise) just until the clatter stops. This position is what is termed "zero lash." Slowly tighten the nut 1 / 4 turn then wait about ten seconds for the idle to smooth out. Repeat this until the nut is tightened one full turn past zero lash.
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CAUTION
You must wait until the engine smooths out after each1/4turn past zero lash. Impatience in this case can cause engine damage due to valve interference.

Repeat step 5 for each remaining valve.

  1. FOR MECHANICAL (SOLID) LIFTER ENGINES: Find your intake and exhaust valve adjusting specs in the Tune-Up chart. Use feeler gauges the same thickness as the adjusting specs. Insert the appropriate feeler gauge between the rocker arm and the valve. The feeler gauge should fit with a slight drag. If the gauge does not fit, loosen the rocker adjusting nut until it does. Tighten the adjusting nut until the gauge can be moved with a slight pull. Repeat step 6 for each remaining valve.
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  3. Remove the oil stopper clips and reinstall the valve covers.
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  5. Reinstall and/or reconnect any related items.
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