How To Adjust Valves on a Big Block Chevy

There’s still an engine that is raced, built and loved today that harkens back to an age where mechanics didn’t need an array of computers to determine what was wrong with your car. The big block Chevy may be a dying breed, but one that many a racer still turns to when horsepower is needed without a lot of the hassle.

The technology that drives many of today’s performance vehicles as yet to impact the big block as it has for the smaller LS1 engines. Many enthusiasts argue that the advances that the new motors of today enjoy just might make the big block obsolete. Engines such as the GEN III and GEN IV Chevy LS engines, or the cutting edge flat plane 5.2 liter engine in the new Ford Shelby are taking 8 cylinder performance and redefining it.

Chevy big blocks have been around since the mid 50’s, and today we’ll be showing you how to adjust valves on a big block Chevy just like your dad did. Before we go over our how to adjust valves on a big block Chevy Guide, let’s take some time to discuss what you’ll be adjusting, namely Valve Lash.

What is Valve Lash?

This term refers to the tolerance between the valve stem tip and the top of the rocker arm. This tolerance is set by Chevy to ensure proper seating and positive combustion chamber pressures.

Usually this valve lash tolerance is given to you in a range, meaning the lowest number is the minimum number at which you should run an engine, and the range goes to the highest you should have your lash adjusted to.

What’s the difference?

Excessively low valve lash or tolerances that are too loose can cause your engine to run roughly and lose power. Because your combustion chamber is not properly sealing as Chevy intended, your engine may run poorly.

Excessively high lash or tighter tolerances can significantly decrease the life of your valvetrain components. If you are unsure  of what range to adjust your big block Chevy, give us a call at 1-888-776-7022 to speak to a rep or ask your local mechanic.

How To Adjust Valves on a Big Block Chevy

Our How to adjust valves tutorial assumes you know the inner workings of your big block Chevy, and are comfortable removing parts and accessing your valvetrain. If you are in need of further assistance, please leave us a question in the comment box below.

Tools you will need

• Socket set
• Allen set
• Breaker bar
• feeler gauges
• Dial tool (if needed)

To begin our How To Adjust Valves on a Big Block Chevy article, you will need to rotate the camshaft until the lifters rest on the back of the cam. To tell this outside of the car, you can tell when you are rotating the cam when these lifters “click over” as it were. On most big block setups, this means that the alignment dot on your cam gear sprocket will be at the 12 o’clock position and the alignment dot on your crank gear is at six oclock.

Get a preliminary measurement by checking the rocker arm for excessive play between the valve stem and the arm. If there is you will need to eliminate this gap by tightening the bolt on your valve stem until there’s sufficient contact and resistance. You are looking to set your lifter to zero lash with zero preload, this is setting the stage for you to check the rest of your tolerances.

With your lifter set to zero preload you can now set a socket wrench onto the bolt and in the UP position, and then rotate a full turn. You must do this for cylinder 2, 5 as well as 7 on the intake side and match the exhaust side to 3, 4, and 8.

Continue until you have completed valve adjustment for all cylinders, and when you are ready to tighten it down carefully use your Allen and spanner wrenches. Use the allen and insert it into the center of the bolt and the spanner wrench will prevent you from losing your adjustment. Tighten it down and torque to specification for your motor in question.

Double check your work after tightening each bolt to ensure that you have dialed in the preload correctly. Rotate the engine until the engine rests in the number 1 firing position. Double check your cam gear and crank gear alignment dots again. This time you will be tightening cylinder 3, 4, 6 as well as 8 by hand, and then giving it another full turn using the spanner wrench.

Rinse and repeat for cylinders 2, 5, 6 and 7 on the exhaust side of the big block Chevy engine. Don’t forget to carefully use the allen and spanner to tighten your tolerances and double check after each adjustment. Do not strip or overtighten your poly-nut, replace if you see any abnormal wear or damage to this nut.

Now that you know how to adjust valves on a big block Chevy, you’ll need to replace the manifolds and valve covers and fire up the vehicle to listen for any further valvetrain noise. Have any questions about valve lash, or adjusting the valves on a big block V8 Chevy? Leave them for us below.