More on adjusting hydraulic valves

May 1, 2008 | By Richard Prince


Concerning the question in a previous issue about adjusting hydraulic valves on a Chevy (March), it is not necessary to use a vacuum gauge to adjust the valves. Once you have turned the valve even one-quarter turn past the point where there is no play, you are now at zero clearance due to the hydraulic action of the lifter.

No matter how far down you turn the valve, as long as you don’t hit bottom,

the hydraulic action will be exactly the same. The only reason they say one full turn on most Chevy V-8s is to put you in the middle of the travel of the lifter. Thus, you could sustain the greatest amount of wear in the system before you reached a point where the valve was out of adjustment. They do this because they know that most motorists will never check valve clearance over the life of an engine.

Some racers adjust their valves only the one-quarter turn down on the theory that if their lifters pump up at very high RPM, they can’t pump up very far. They don’t worry about the wear factor because they know they will check their valves more often.

With a 3/8-24 stud, one turn, the stock setting, equals .041-inch movement into the lifter.

The difference in length of a hot or cold pushrod is only a few thousandths, so cold, warm or hot makes no difference. I prefer not to work on a hot-oil spitting engine, so I always adjust valves on a cool, non-running engine and have never had a problem.


Thank you for taking the time to share your opinion with other readers.

I do, however, disagree with your assertion that, “No matter how far down you turn the valve, as long as you don’t hit bottom, the hydraulic action will be exactly the same.”

The distance that the pushrod seat in a hydraulic lifter moves down from its retaining lock ring is called preload, and the hydraulic action of the lifter will vary as the preload varies.

Too much preload, which is normally defined as a distance from the underside of the lock ring to the top side of the pushrod seat that’s greater than .060inches, can be harmful.

As engine rpm increases, engine oil pressure normally increases as well. The hydraulic action of the lifter will “pumpup” the pushrod seat and can cause the valve to open higher and remain open longer. If this happens, cylinder pressure decreases and engine performance decreases as well.

A manifold vacuum gauge is a convenient way to get an idea of how cylinder pressure is changing, and this helps explain why a vacuum gauge is a reliable indicator for when hydraulic valves are properly adjusted.

It is not the only way to accurately adjust hydraulic valves, however.

They can be adjusted cold with the engine not running as you indicated, but

simply turning the rocker arm nut a set distance after all play between the push rod and lifter is taken up is not a correct technique. In order to obtain proper adjustment for each lifter, it should be located on the base circle of the cam lobe.

An easy rule of thumb for determining when a lifter is on the base circle is as follows: rotate the engine by hand in its normal direction of rotation and observe the action of the exhaust valve. When the exhaust valve just begins to open, the lifter for the corresponding intake valve is on its base circle and can be adjusted.

To adjust it, loosen the rocker nut until the pushrod spins freely. Wait a couple of minutes for the spring in the hydraulic lifter to move the pushrod seat up and against the lock ring (this is called the “neutral” position). Once the lifter is in neutral position, simultaneously spin the pushrod and slowly tighten down the rocker nut.

Once you feel slight resistance to the rotation of the pushrod, you have taken up the play between the pushrod and lifter and are at zero lash.

Tighten the rocker nut one-half to one full turn from zero lash and the lifter will be within the desired range of .020-.060 inches of preload.

Once the intake is adjusted, rotate the engine again and watch the intake valve. It will open and then close as the engine is rotated.

When it is almost completely closed, that cylinder’s exhaust valve lifter is on the cam lobe’s base circle and is, therefore, correctly positioned for adjustment.