Adjusting Valves

 

Adjusting Valves

 

 

There are several methods of adjusting valves, rockers, setting lash, or whatever you want to call it, on older chevy V8's. The following is a tried and true, accurate and non-messy way to do it. Both hydraulic and solid lifters are covered. Unless you're a glutton for punishment, you DO NOT need to have the engine running to accurately adjust the valves. When was the last time anyone saw Warren Johnson or Bruce Allen adjusting rockers with the engine running on their NHRA Pro Stockers? The engine can even be cold as I'll explain! There is enough range in the plunger of a hydraulic lifter(at least two full turns of the adjusting nut past zero lash) that it makes no difference whether the engine is hot or cold. With solid lifters you can warm the engine first or add .002 to .003 to the hot lash specification for iron heads to adjust them cold. For an aluminum head subtract .003 to .005 from the hot lash specification to adjust cold. It's more important to be precise, with solid lifters, so it's better to warm the engine first, unless you know exactly how much your lash changes between hot and cold. With either type lifter, there is one truly accurate way to position the engine internals to adjust each rocker. It's called the "exhaust open/intake closed" method. This ensures the lifter is on the center of the base circle of the cam lobe for the rocker you're adjusting. This is especially important with solid lifters due to the long take up ramps on the lobes. To perform this, bump the starter until the exhaust valve for the cylinder just starts to open. The intake valve is now ready to adjust. To adjust the exhaust rocker bump the starter until the intake valve for the cylinder fully opens and just starts to close. To properly adjust hydraulic lifters, position the valve as previously stated, then loosen the rocker just to the point of zero lash. That's where ther would be clearance between the rocker and valve if it were loosened any further. To determine this point, loosen it past that point until you can wiggle the rocker and freely spin the pushrod with your fingers. Then tighten it slowly until you feel a slight drag on the pushrod when spinning it with your fingers. It will take a little practice. Then tighten the rocker arm adjusting nut 1/4 turn (for high performance engines) to one full turn (per Chevy service manuals) more. For serious race-only engines you can even lash hydraulics at .002 (hot) to prevent lifter pump-up at high RPM. Those with solid lifters already know, or should know, how to adjust their rockers with feeler gauges with the valves positioned as previously explained. With these methods you can be sure you're setting your rockers as accurately as possible while keeping everything neat and clean. Of course, if you like giving yourself, your car and garage floor a hot oil bath, then feel free to do it with the engine running.