From Century Performance:
Valve Adjustment Procedure - The Quick and Accurate Way:

    First, view this little chart below for Small and Big Block Chevy Engines that I made and see if you can understand it. There is more of an explanation below the chart. For other engines you will use the firing order that matches your engine to create a similar chart. This chart is based upon "opposite" cylinders of your firing order. (see below)

Intake Valve Adjustment:   ENGINE OFF!

                +
                  with #1 cylinder Intake Valve at full valve lift .... Adjust #6 Intake Valve
                +
                  with #8 cylinder Intake Valve at full valve lift .... Adjust #5 Intake Valve
                +
                  with #4 cylinder Intake Valve at full valve lift .... Adjust #7 Intake Valve
                +
                  with #3 cylinder Intake Valve at full valve lift .... Adjust #2 Intake Valve
                +
                  with #6 cylinder Intake Valve at full valve lift .... Adjust #1 Intake Valve
                +
                  with #5 cylinder Intake Valve at full valve lift .... Adjust #8 Intake Valve
                +
                  with #7 cylinder Intake Valve at full valve lift .... Adjust #4 Intake Valve
                +
                  with #2 cylinder Intake Valve at full valve lift .... Adjust #3 Intake Valve 

Exhaust Valve Adjustment:   ENGINE OFF!

        You will notice that this is the same procedure and sequence as the intake valves listed above. Only now you are adjusting ONLY the exhaust valves the same way.

                + with #1 cylinder Exhaust Valve at full valve lift .... Adjust #6 Exhaust Valve
                + with #8 cylinder Exhaust Valve at full valve lift .... Adjust #5 Exhaust Valve
                + with #4 cylinder Exhaust Valve at full valve lift .... Adjust #7 Exhaust Valve
                + with #3 cylinder Exhaust Valve at full valve lift .... Adjust #2 Exhaust Valve
                + with #6 cylinder Exhaust Valve at full valve lift .... Adjust #1 Exhaust Valve
                + with #5 cylinder Exhaust Valve at full valve lift .... Adjust #8 Exhaust Valve
                + with #7 cylinder Exhaust Valve at full valve lift .... Adjust #4 Exhaust Valve
                + with #2 cylinder Exhaust Valve at full valve lift .... Adjust #3 Exhaust Valve 

 
Now I'll Provide an Explanation:
 
What you see above is adjustments being made on "opposite" valves on the engine cycle. The small and big block Chevy engines use a firing order of 1-8-4-3-6-5-7-2. What you do is separate the order into the two sides of the firing order. These are "exact" opposites that put the opposing valve at the correct location for adjustment, meaning the back side (base circle, or heal) of the cam lobe (see image at left).
 
Looking at the chart below you will see that #1 is opposite #6, and vice-verse, on through the firing order. This holds true for both intake and exhaust valves.
 
This procedure works on most V8 and V6 engines.
 
1  « - »  6
8  « - »  5
4  « - »  7
3  « - »  2
 
 
 
If the lifter is anywhere other than on the heal of the camshaft where there is NO ramp contact you will have incorrect lash. This position is required for each valve before you attempt to perform adjustments. The chart and procedure above ensures that the lifter is on the backside of the cam lobe for each valve. When you were previously instructed by the auto shop teach or service manual to position each cylinder at TDC (piston at Top Dead Center) you will find often times that this is not the correct procedure to obtain the proper lash setting. View the image at right and you can see the required position of the cam lobe to be able to correctly adjust the valve lash.
 
You want to be sure that the lifter is positioned on the heel of the cam lobe which will guarantee that the valve you are adjusting is fully closed. Any other position and your adjustments will not be accurate.
   

 
What about the actual adjustment procedure?
 
Hydraulic Cams:
 
Let's get to the actual wrench turning ... how many of you read or were taught that with a hydraulic lifter camshaft, you adjust it down to where there is pushrod resistance (zero lash) and then turn it down 1/2 to 3/4 turn?  Well, if you did this, you more than likely have the valves not closing all the way!
 
Neutral and with Pre-LoadThe typical hydraulic lifter requires an adjustment that is roughly half the available travel of the plunger. If an average hydraulic lifter plunger has a range of 0.060" of travel from fully compressed to its static height with the pushrod seat against the retaining ring, half of that distance will be 0.030". This means that you adjust valves by the depth that the plunger in the lifter drops. If adjusted too tight (the plunger fully compressed) the valves do not close all the way, and if too loose the pushrod seat will rattle and do not open properly, damaging the lifter. How do you get to a 0.030" plunger depth? On newly assembled engines I will actually use a dial indicator and measure the distance of travel on the new lifter. On an engine in the car this is a bit different, and harder to do..
 
I have two ways that I use to adjust hydraulic lifters. One uses the "clean" method with the engine turned off, and the other is the messy way with the engine running and squirting oil everywhere.
 
 
Engine "OFF" Hydraulic Lifter Adjustment:
 
Warm the engine by running it until it gets to operating temperature (15-minutes or so). Have all your tools ready and then quickly remove the valve cover(s) and start the adjustment procedure by using the chart above. With the #1 Intake valve at FULL LIFT (this means that you spin the engine until the Intake valve on the #1 cylinder is fully open ... you can tell this by the rocker arm pushing the down until it goes no further) you can now adjust the "opposite in firing order" cylinder (see the above chart). In the small and big block Chevy engines this is the #6 cylinder. Loosen the rocker (if using roller rockers there is a Jam Nut that you must loosen with an Allen Wrench). Now, with two fingers spinning the pushrod between them to feel for resistance you easily snug the adjustment nut. When you feel resistance STOP, now you will adjust the nut down "Only" 1/8-1/2 turn. If you operate your engine a consistent high RPM, use the lighter setting (1/8 turn).
 
 
What is 1/4 turn? (see image below)
 
what constitutes 1/4 of a turn?Imagine the hands on a clock. You have the obvious 12:00, 3:00, 6:00, and 9:00 o'clock positions as well as the numbers in-between those. If you start with your wrench at the 12:00 position and turn it clockwise to the 6:00 position you have just made 1/2 turn. Going from 12:00 to the 3:00 position would be 1/4 turn.
 
Now, you will do this for all the intake valves and then do the exhaust valves the same way.

        PRECAUTION: If you have an older high mileage engine which the lifters bleed off pressure (drain the oil out of the lifter body), you can improperly adjust your valves. You need oil in the hydraulic lifter to be able to get an accurate setting. If you repeatedly adjust the valves by this procedure and they are still not correct, you probably have lifters bleeding off during adjustment. You have two options: Replace the Lifters  -= or =- adjust the valves using the "HOT" running method described below.

 
 
 
Engine RUNNING Hydraulic Lifter Adjustment:
 
So you really like messes? This has to be one of the most miserable maintenance procedures if you do not properly plan ahead.
 
Some helpful hints:

    * Adjust only one side of the engine at a time.
    * Use oil restrictors on the rocker arms, or better yet a butchered up valve cover that has an access cut into the top of it to facilitate adjustment access.
    * Stay calm ... you WILL get burnt, you WILL make a mess and you WILL not look forward to doing this again, especially if you screw up the first time.
    * Using a mechanic's stethoscope can substantially make this procedure easier.

Adjusting hydraulic lifters with the engine running is not one of my favorite activities (as you can tell). With the above considerations addressed, start the engine and allow it to warm up. Begin to loosen one of the rocker arm adjusting nuts. You should hear the valvetrain just start to "clatter". Slowing tighten it down until the "clatter" just stops and then turn it 1/4 - 1/2 turn additional to set the plunger depth (lifter preload). Continue this procedure on all the valves. If you hear excessive noises or the vehicle runs crappy you will be doing the procedure again. As stated above, if you have access to a mechanic's stethoscope, you can set the end at the top of the rocker stud to listen to the noise a loose adjustment makes, which will make finding "zero" lash easier.
 
IMPORTANT WARNING: If you make a mess, PLEASE use environmentally conscious methods to clean up any oil spills and then check your oil level. You would be surprised at how quickly, and how much oil can spill when performing valve adjustments with the engine running.
 
 
Solid Lifter Adjustment:
 
First warm the engine to operating temperature (about 15-minutes) and then quickly remove the valve covers. Follow the chart above. With the #1 Intake valve at FULL LIFT (this means that you spin the engine until the Intake valve on the #1 cylinder is fully open ... you can tell this by the rocker arm pushing the down until it goes no further) you can now adjust the "opposite in firing order" cylinder. In the small and big block Chevy engines this is the #6 cylinder. Loosen the rocker (if using roller rockers there is a Jam Nut that you must loosen with an Allen Wrench).
 
Based upon your cam card (cam specs provided by the camshaft manufacturer) you should know what the valve lash setting should be in thousandths of an inch. Let's say that your recommended valve lash setting is .022". Get out the .022" feeler gauge and place it between the top of the valve stem and the rocker arm tip. Snug down the rocker "just" until you begin to fell resistance. You should be sliding the feeler gauge back and forth gently on stock style slotted rocker arms, or gently side-to-side if using roller tip rockers. The valve lash setting should not be tight ... the feeling should be about the same as putting a table knife through a stick of cold butter. Not too hard, not too soft. Hopefully you are using "positive-lock" rocker arm retention fasteners instead of just cheap pinched rocker nuts or Nylox. If using rocker nuts your job is done, go to the next valve. If using positive-locks, hold the body of the lock in place with a box end or open end wrench (there are special tools for this available) and then tighten the Allen set screw in the center of the posi-lock.
 
NOTE: In most cases the Allen set screw will make a slight "click" when it is tight.
 
 
Compensating for a Cold Engine When Adjusting the Valve Lash
 
When installing a new camshaft, your engine will be cold. The problem is that the provided lash specifications are for an engine that has been running long enough to be at normal operating temperatures. So, what are you to do? There is a standard correction factor that can be used to get you close to the required settings. You must now consider the material alloys of the engine parts, because the thermal expansion of these components affect the valve lash in different ways. Therefore the correction factor used for your lash setting will depend upon whether the cylinder heads and block are made out of cast iron or aluminum.
 
Take the "hot" setting provided to you in the cam manufacturer's catalog or from the cam card that came with your camshaft. Use the figures below to alter the original lash specifications to get a "cold" lash setting.

          o Using iron block and iron heads, add .002"
          o Using iron block and aluminum heads, subtract .006"
          o Using both aluminum block and heads, subtract .012"

Remember this correction adjustment is only approximation, and it is only meant to get you close for the initial start up of your engine After the engine has been properly warmed up to normal operating temperatures you must go back and reset all the valves to the specified "hot" valve lash settings.
 
 
Using Valve Lash to Help Tune Your Engine
 
Most people do not realize that you can make subtle performance improvements by opening or closing the recommended lash settings.
 
The intake and exhaust valves cannot move until all the running clearance (valve lash) has been taken up. Therefore, the amount of valve lash you use affects the engine's performance. For example, if you decrease the amount of (hot) valve lash, the valve will open slightly sooner, provide slightly more lift (valve opening), and close later. This makes the camshaft look bigger to the engine, due to this slight increase of duration and lift. If you increase the amount of (hot) lash the opposite occurs. The valve will open later, provide slightly lift less, and close sooner. Now your engine sees a smaller cam with slightly less actual duration and lift.
 
You can use this tuning method to experiment with what the engine responds to, then keep the setting that works the best. Just remember, the more lash you run, the noisier the valve train will be. If the clearance is excessive it can be harsh or damaging to other valve train components. Therefore, for prolonged running of the engine it is not recommend to increase the amount of lash by more than +0.004" from the recommended setting. Nor is reducing the lash by more than -0.008" recommended.
 
The common gains that people see will be that by reducing the lash will increase top end (upper RPM power) horsepower, and increasing the lash can improve low end torque and acceleration.
 
 
Closing Remarks:

    * As mentioned above, you can change the power band a bit on an engine using a solid lifter camshaft by varying valve lash settings. A looser lash setting increases the low-end power of the engine where a tighter lash increases top-end power. Also, be careful because the valve lash is the "Cooling Time" that the valve needs on each cycle. If you have too little, or no lash, you take a chance of burning the valves.
    * Using roller rocker arms dramatically increases valve guide life, increases horsepower and also maintains better valve lash settings. Use them when you can! Shaft style rockers are best (less deflection). Stainless steel rockers provide less "over the valve weight", which is GOOD. Aluminum, though less expensive will deflect more and increase the actual weight over the valve stem. The added weight may not seem critical to you, but this is considered rotational weight, which slows down all the components related to it.
    * Additionally, too loose a valve lash setting can damage the valve stem and increase possibility of the roller rocker tips failing. If using OEM style stamped steel rocker arms you could fracture the arm or gall the fulcrum.
    * Engine materials, engine operating RPM, and valvetrain deflection contribute to varying valve lash settings. The higher the RPM, the cheaper the parts you use and the different types of materials contribute to sooner need for valve lash adjustments. (By the way, while you are in there ... test your valve spring pressures).
    * There is FREE horsepower when using a Roller Cam ... if you can afford it, do it. Plus, when using a roller cam, you can change camshafts without the need to change lifters, which is mandatory with Hydraulic or Solid "tappet" cams.