Setting Valve Lash

Setting valve lash is something that seems to be often over looked when it comes to weekly maintenance. Ideally, it is something that needs to be checked every week before heading to the track but it is recommended to run your valves at least every two to three races. A big reason this is usually skipped on the weekly maintenance list is because a lot of racers do not know how. We put a little something together that will hopefully give you some insight on the proper way to set your valve lash.

The first step in this process is cleaning the entire top of the engine off with compressed air to make sure you have a clean work area that will not allow any dirt or debris into the engine. Gather all the tools needed for the job and get them ready to use on the car. Using quality feeler gauges is a must, to keep from accidentally using the wrong size gauges, bend the correct gauges on a 45° angle. Take the spark plugs out and lay them in order so they can be returned to the same cylinders when the job is complete. Next, take off the valve covers and put all the nuts and bolts far enough from the motor so you don't have to worry about them falling into the engine. Take a flashlight and look over the springs and any other mechanical parts very closely for any cracked or missing parts. Intake and exhaust valve lash settings should be written in a book, as well as on the intake, along with the lash settings. Writing spark plug gap and timing settings on the intake is recommended also. The reason for this is so you will have all of the necessary information nearby when things get hectic at the track.

The valve lash is always measured between the tip of the valve stem and the bottom surface of the rocker that pushes the valve. Start at the number one cylinder, which is on the left side (driver's side) at the front of a GM engine (on Ford motors, the number one cylinder is the front cylinder on the passenger side.) Adjust the exhaust first. Don't try to get the intake and exhaust at the top together, but rather do them one at a time. Bump the engine over until the exhaust valve (the header pipe is below this valve) is at the top of its stroke. At the same time the intake valve should be down and just starting to come up. You will be able to wiggle the exhaust rocker, unless the setting is way too tight. You might have to turn the engine over several times until you hit it just right. Place the correct thickness feeler gauge between the rocker and tip of the valve. The feeler gauge should go in with a little bit of pressure applied, not too easy and not too hard, just a light drag. The shaft mounted rockers have the adjustment screw on the push rod end. Stud mounted rockers are adjusted at the stud in the middle of the rocker.

After adjusting each rocker, tighten the lock nut and check it again. If the adjustment still feels right with the adjuster locked down, you can move on to the intake valve. To get the intake valve in the right position bump the engine until the exhaust valve just begins. With many cams, the setting for the intake and exhaust valves are different, so be sure you use the right feeler gauge. Continue through all the valves using the same procedures. You can also make it a practice to check the valve spring pressure with a valve spring gauge. This is a good way to see if your springs are getting soft, or if you have a broken or cracked spring. When you complete setting all the valves, check all the adjusters one more time. Now is a good time to check the header bolts since they are often more accessible with the valve covers off and spark plug wires out of the way.

Next, reinstall the spark plugs. If you have aluminum heads put a small amount of anti-seize on the threads to make them easier to remove next time. Attach the plug wires making sure they are on the right plugs (a very common mistake, especially when in a hurry) and hear them snap. Check the top of the heads once more for anything that is not supposed to be in there, and then reinstall the valve covers.