How to Check and Set Valve Lash
Running the valves should be done after every night if racing. This is a good way to detect any early signs of possible engine failure. To get started, you need to remove the valve covers. Once valve covers are removed, inspect it to make sure the cylinder head is free of any debris. Pay close attention to make sure there are no metal flakes or pieces laying in the head. Also, take note of the oil in the head, it should be the same color as when oil was poured into the engine. If the oil has a milky color, this can be caused by an engine where the fuel system was not set correctly. Or if any water is present, you could have more serious issues. There may be some traces of moisture if the air was humid when the engine last ran.
The next step is to remove spark plugs. You do not have to remove the plugs, but it makes it easier to rotate the engine if you do. I like to inspect the plugs once they've been removed. They should have a nice tan or light brown color if the engine was tuned correctly. If plugs are ghost white, the engine was too lean. Dark brown or wet means too rich and black is possibly burning oil.
Now that the plugs and valve covers are removed, we are ready to check valve lash. I like to check by starting with the intake of the number one cylinder and going in the firing order of the engine. This makes it easy to keep track of which valves have been checked with minimal rotating of the engine. Rotate the engine so that the number one exhaust valve just starts to move. You can now check the intake valve. I first spin the pushrod to make sure it spins free. If the pushrod does not spin, it can be caused by no valve lash or being bent. If the pushrod is bent, you need to investigate further what the cause was.
The most common causes are the valve hit a piston, the valve lash is too loose, or there is a lifter issue. As long as the pushrod spun freely, you can check lash. Check with the engine builder or cam manufacturer for the correct lash. Next, insert the correct feeler gauge in between the top of the valve stem and under rocker tip. Speedway Motors offers these Valve Lash Feeler Gauges. This should be a snug fit. If you can spin push rod when the feeler gauge is inserted, the valve lash is too loose. If you have to force feeler gauge in, the valve lash is too tight.
If the lash needs to be adjusted, you will need to loosen the lockset screw inside of the poly lock with your wrench turn poly lock. Once you have the desired lash tighten set, screw inside of the poly lock. Speedway Motors offers this Valve Lash Rocker Wrench and Valve Lash Torque Wrench to make this easier. Adjust the shaft mount rockers by loosening the nut and adjusting with hex key wrench. Make sure the set screw or jam nut is tight when lash adjustment is done. Repeat this step for all intake valves.
Now we move to the exhaust valves. Rotate the engine so the number one intake is ¾ of the way closed. Spin the exhaust pushrod to make sure it is free. Once again, insert the proper feeler gauge above the exhaust valve stem and below the rocker tip. You want the fit to be the same as how we checked the intake, snug, not too tight not to loose.
Repeat this for all seven exhaust valves. After all the valves are set, install the plugs and valve covers. Some cams may require to set lash that the intake is fully open to check exhaust and exhaust is fully open to check the intake. You want the lifter to be on the backside of the cam and not on the ramp of the cam when checking lash. Whichever setting gives you the largest lash is the one you will want to use.