It may not be pleasant, but setting the valve lash on a high-performance engine is a skill that must be learned. The reality is that even the most savvy engine masters had to learn about lash at one time or another. Whilehands-on experience is invaluable, with a little guidance you can easily learn to lash valves without breaking a sweat. Follow along as we run through the valve lash procedure on a typical small-block Chevy.
It all starts beneath the valve covers, where 16 rockers (two per cylinder) are responsible for taking up the valvetrain slack during engine operation. Whether lashing valves is performed in a vehicle or on an engine stand, it's best to remove all of the rockers and spark plugs first. Depending on where the engine stops its rotation, a minimum of two cylinders will be left attempting to open or close their valves. This places those rockers and valvesprings in a compressed state, and the rocker nut should not be removed until the spring is relaxed to its resting installed height. Removing the rocker nut while under valvespring pressure will cause the rocker stud to strip its threads. Before removing a pressurized rocker nut, rotate the engine until the valvespring comes to a complete rest against its valve lock.
From here we moved on to the installation of our 16 rockers. Our hydraulic lifter-equipped engine was rotated until the No. 1 exhaust lifter had risen and began to fall. Several degrees into the exhaust lifter's falling cycle we stopped the engine and began work on the No. 1 cylinder's intake valve. We placed the new rocker over its stud with the flat part of the rocker's center facing upward. Next we used one hand to move the pushrod up and down while the other hand tightened the nut until the rocker's pushrod cup lightly touched the pushrod. With minimal vertical pushrod movement being set by hand, there are three methods of setting various valve lash.
Intake Open/ Exhaust Close
The operation of any four-cycle valvetrain-equipped engine will follow the intake open/exhaust closed (IO/EC) formula, regardless of the engine manufacturer. The four-cycle camshaft design dictates that each lobe of the camshaft within the same cylinder be positioned roughly 180 engine degrees apart. With reference to the first-generation small-block Chevy camshaft in the captions, it's easy to see that the first group of lobes operates the intake and exhaust valves of the No. 1 and No. 2 cylinders. With this visual understanding it's easier to see how the resting valve can move across the backside of the camshaft lobe while its neighboring valve reaches its peak lift and begins to fall. The backside of the cam lobe places minimal pressure on the individual valvetrain piece, making it possible to adjust hydraulic or solid lash.