It's a skill that every hot rodder should know by heart. It can also be one of the more confusing aspects of engine assembly. We're talking about setting valves. We'll show you a very simple way to set valves that can be used on any four-stroke engine of any make, model, or description from a Briggs & Stratton to a monster Pratt & Whitney radial aircraft engine. Once you commit this simple procedure to memory, you'll be able to amaze and impress your friends with your engine knowledge and prowess.
EO-IC
That cryptic sequence of four letters is all you have to remember when it comes to setting valves on a four-stroke engine. More specifically, it refers to Exhaust Opening-Intake Closing (EO-IC). The plan behind setting valve lash is the same whether it's for a solid-lifter-style camshaft or lifter preload for a hydraulic-lifter camshaft. In the prehistoric days, you roughly set the valves, started the engine, and then set the >> lash with the engine running, splashing oil all over the engine compartment.
This was messy and required you to work very quickly. The easier way to do this is to set the lash or preload with the engine static. That way you can take your time. Setting lash requires that the lifter be on the heel, or base circle, of the camshaft. Since the cam is impossible to see installed in the engine, we have to rely on other cues.
Ready, Set, Go
Before you start, make sure the transmission is in Park with the emergency brake set, or if the car is equipped with a manual transmission, make sure the trans is in Neutral with the parking brake set and the coil wire or distributer harness disconnected. The best way to crank is to use a Remote Starter Button to turn the engine over with the starter motor. If you don't have one of these tools, you can have a friend in the cockpit bump over the engine with the ignition switch.
We like to start at the front of the driver-side engine bank with No. 1 cylinder. Contrary to what you might think, the first valve at the front of the left bank on the small-block Chevy is actually the exhaust valve. If you're not sure about whether a valve is an intake or an exhaust, the easiest way to tell is to line up the valve with either an intake or an exhaust port. If the engine has headers, the exhaust is easy to identify. Since our small-block only has two valves per cylinder, if the rocker is not lined up with an exhaust port, then it must be an intake port and vice versa.
To set the first pair of rockers, bump the engine over and watch the exhaust rocker arm. When it opens roughly a third of its total >> (exhaust opening--EO), stop and set the intake rocker arm. If you were to look at a cutaway of any four-stroke engine, when the exhaust valve just begins to open, the intake lobe would be on its base circle. That is when you want to set the intake.
To set the intake, back off the poly lock or adjustment nut until you know there is clearance. Then slowly tighten the nut until you can feel a slight resistance while twirling the pushrod between your fingers. This is zero clearance between the lifter, pushrod, rocker, and valve. If the engine is equipped with solid lifters, use a feeler gauge to establish the proper clearance between the rocker arm and the valve-stem tip. This is usually around 0.018 to 0.024 inch of clearance, but use the manufacturer's recommended lash. You want to establish a "feel" or slight tug on the feeler gauge and use that same amount of resistance for all 16 valves.
If you are setting preload on a hydraulic lifter-equipped engine, the process is a little different. Again, tighten the poly lock until all clearance is eliminated which is ZERO LASH, and then tighten the adjuster another half-turn. This preloads the small piston in the bore of the lifter. Hydraulic oil pressure inside the lifter will maintain this preload throughout engine operation. Some manufacturers may require more preload, but a half-turn is a safe setting that most companies use. This half-turn also reduces the amount of distance the lifter's internal piston travels if the lifter "pumps up" due to an engine over-speed condition.
Now that we've set the intake lobe, we're ready to set the exhaust. Bump the engine over again and watch the intake lobe this time. Continue to bump the engine past max intake valve lift and stop when the intake is about halfway down on the closing side (IC--intake closing).
Now set the lash or preload on the exhaust valve for the same cylinder. Once you've done that, you're ready to move to the next cylinder. You don't have to do the engine sequentially. In fact, you could set lash by the firing order. However, we like to run down the cylinders from front to back to make sure we don't lose track of which rockers we've set. We end up bumping the engine over a few extra times this way, but it minimizes the chance of losing track of where you are and possibly missing a valve or two.
To review, setting valves is actually pretty simple. You can set these valves starting with either the intake or exhaust. Start at the front of the driver side, bump the engine over until the exhaust valve just starts to open (EO), then set the intake valve. Once you've done that, bump the engine over again until the intake valve is roughly halfway down the closing side, then set the exhaust valve. Once those two valves are done, move on to the next pair.
The only thing to remember is to work on one pair of valves for a dedicated cylinder before moving on. Once we've set all the valves on one side, we like to go back over all the adjusting nuts to ensure they are all tight. That way, we know we didn't miss one.
Once you've set both sides, replace the valve covers and reconnect the ignition system. Then fire up the engine and listen for any clattering or noise that may indicate that you've missed one or more valves. If the engine runs smoothly and exhibits no excessive noise, you're done.
