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. In this story, 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.
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). But before we let you in on the secret, let's go over some basic engine theory to put you in the proper frame of reference for our little valve-lash adventure.
In the four-stroke cycle, the piston moves downward as the intake valve opens to allow fresh air and fuel into the cylinder. Somewhere around Bottom Dead Center (BDC), the intake valve closes. The piston moves up, compresses the mixture and just before Top Dead Center (TDC), the spark plug fires and ignites the mixture resulting in the combustion that pushes the piston down the cylinder.
With the piston around BDC, the exhaust valve opens, and as the piston again moves upward, the exhaust valve begins to close. All of this is pretty basic stuff, but it's necessary to understand how and when the valves open in a four-stroke-cycle engine.
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.
The first thing to do is make sure the engine is fully warmed up. Then disconnect the coil wire from the distributor and ground the wire to the intake manifold. If your engine is equipped with an HEI distributor, disconnect the large red 12-volt feed wire to the cap to disable the ignition. Next, pull one valve cover to start the process. If you are installing new rocker arms or the engine is new, install all the rockers and run the jam nuts down until the rockers are snug. We suggest using poly locks rather than locking nuts, because the poly locks will lock into place and not move, and they are easier to set and don't tear up the threads like locking nuts do.
Be sure to choose the right poly lock for your application since there are several different styles from several companies such as ARP, Comp, Crane, and ProForm. The height of the poly lock can vary depending upon the style of roller rocker you are using. You want to avoid interference between the poly lock and the rocker arm.
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. The best way to crank is to use a momentary-switch 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 turn on 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, 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. After you congratulate yourself on a job well done, you can move on to that next project. See, that wasn't so hard, was it?
There are entirely too many rocker arms, poly locks, and stud combinations to list here. The best move is to consult the Comp Cams, Crane, or other valvetrain company catalog for a complete listing.
Once you've removed the valve...
Once you've removed the valve covers and disabled the ignition, the next thing to do is to identify which rocker is which. The front rocker on any small-block is an exhaust rocker, not an intake. The easiest way to tell exhaust from intake is to line up the rocker with either an intake or exhaust port.
With the car in Park or Neutral...
With the car in Park or Neutral and the emergency brake set, have a friend slowly bump the engine over and watch the exhaust rocker. When the exhaust rocker just starts to open the valve, stop. Now you can adjust the intake rocker. As you tighten the adjuster nut or poly lock, you can tell when you reach zero lash because the pushrod will tighten up as you spin it between your fingers. These are Crane Gold Race roller-rocker arms.
Now set the intake rocker...
Now set the intake rocker by achieving zero lash and adding an additional half-turn to preload the lifter. This is on a hydraulic-cam engine.
Now bump the engine over again...
Now bump the engine over again until you see the intake rocker go past max lift and start its way down. Roughly halfway through the closing side, stop. Now you can set the exhaust rocker by first finding zero lash and then adding an additional half-turn of preload.
These are stock rockers with...
These are stock rockers with stock pinch-type rocker nuts. We prefer to use poly locks on even stock rockers because the factory locking nuts tend to tear up the rocker-stud threads. They are also prone to loosening over time.
This is a slick ARP piece...
This is a slick ARP piece called a Perma-Loc that uses a 12-point head and a shoulder to prevent the wrench from slipping past the hex portion of the poly lock.
If you look in a Crane or...
If you look in a Crane or Comp Cams catalog, you will notice several different styles of poly locks. Be aware that the shank diameter and length are important since the poly lock must not touch the rocker arm as it moves through its travel.
If you find yourself checking...
If you find yourself checking lash often, you might want to invest in one of these slick tools from ProForm. There are several versions according to the size of the poly lock hex and Allen locking screw. The tool holds the Allen T-handle, which is nice when you need that third hand to set lash.
Also be aware that there are...
Also be aware that there are both 3/8-inch and 7/16-inch studs available for a small-block Chevy. Most stock or mild performance applications use a 3/8-inch stud. The best studs come from ARP.