Mind The Gap: Why Valve Lash Is Important And How To Set It

The valvetrain of an engine is responsible for talking to the camshaft — it makes sure air enters and leaves the engine on time during the combustion process. If you want to keep the valvetrain of your engine happy, it’s important to check the valve lash on a regular basis. We talk with Brad Rounds from T&D Machine Products to learn more about valve lash, why it’s so important, and how to lash valves properly.

Project Number Cruncher uses a set of solid lifters from COMP CAMS, along with a camshaft from COMP, and stud mount rocker arms from T&D. When SAM Tech was finished with our engine, it provided us with an engine care guide so the engine would perform at its best. The valve lash settings were the first thing listed on the guide — that right there should tell you how important valve lash is to an engine. SAM Tech worked with COMP to get the valve lash settings right, and it worked with T&D to make sure the rocker arms were set up right when they were installed. All of this plays a role in making sure your lash is set properly when our building an engine.

Setting valve lash the right way will help your valvetrain last longer and perform better.

Valve Lash Basics

So what is valve lash exactly? There’s always going to be a small gap between the components of the valvetrain, and that’s what valve lash really is. This gap is there so the metal parts of the valvetrain can expand when they warm up and not move the valves in any way. The camshaft’s rotation will move the lifter, and that will close the lash gap right before the valve is opened.

Brad explains why valve lash is so important to any high-performance engine.

“Valve lash has a couple of important functions. First, valve lash gives some room for the engine to grow and shrink during a complete heat cycle. Valve lash must be set properly to keep the valves from being held open when the engine is at its coldest or hottest temperature. Second, lash allows for the lifter to be applied to the cam lobe as gently as possible.”

If you're building an engine yourself make sure you pay close attention to the valve lash numbers provided by each company.

If your engine uses hydraulic lifters, you don’t have to check the lash nearly as often as a solid lifter set up. This is because the hydraulic lifter has a plunger inside that will take up the lash distance. Engines that use solid lifters need to have the lash checked often, since you’re creating the lash yourself.

You really want to be sure that you set the lash the same way each time and you are paying attention to how you do it. – Brad Rounds

Valve lash, though, needs to be checked regularly to catch any possible issues. Each engine will have a different interval when the lash needs to be checked. Project Number Cruncher’s naturally-aspirated 427 cubic-inch LS engine will need its lash checked every time the engine gets an oil change. Your engine will be different based on the parts used, how you use it, and how the engine builder set it up.

You can set valve lash when an engine is hot or cold, but which is the most optimal time? According to Brad, you want to set the final lash when the engine has reached operating temperature.

“Lash should only be set cold after final assemble of the engine. Final lash adjustments should be made when the engine is at its operating temperature. If the final lash is set when the engine is cold, after the engine heats up, the change in lash will alter the duration of the camshaft. Setting lash when the engine is hot guarantees that the camshaft will perform as the cam manufacturer intended.”

Getting Your Valve Lash On

It’s important that you have the right tools for any job, and lashing valves is no different. If you’ve been working with high-performance engines for a while you probably already have the required tools to run valves, but if you’re new to this elevated level of engine maintenance, you might not have what’s needed.

To set valve lash you'll need a simple feeler gauge and a few other basic tools. A special valve lash tool like the one made by LSM Racing Products has a built-in torque wrench to make sure you've tightened everything up correctly.

The good news is that you don’t need a lot of expensive tools to lash valves on most engines. You can actually lash valves with a box-end wrench that’s the appropriate size for the poly-locks on your rocker arms and a T-handle Allen key. There are tools that are made specifically for lashing valves that make the job easier. These tools will be L-shaped with the correct size wrench end to it over the poly-lock. The tool will also have a guide to hold the T-handle Allen key in place while you make adjustments.

If you want the ultimate valve lashing weapon, you can pick up a tool that has an integrated torque wrench that will prevent you from tightening the adjuster nut too much. You’ll also need a set of feeler gauges to make sure you’ve got the right amount of clearance when you set the valve lash.

So, how do you set valve lash on a fresh build? Brad explains how he sets valve lash the first time.

“When the rocker gear is installed during final assembly, I rough in the lash. I will set the lash 0.010-inch tighter than what the manufacturer calls for when the engine is hot. If the engine has aluminum heads on an iron block, typically my rough lash gets very close to manufacturer specs at temperature. After the engine is broken in and up to temp, I will set the lash to the spec on the cam card.”

When you’re building a new engine its important to follow the manufacturer’s guidelines on how to set lash.

There are several different schools of thought about how you should go through the valve lashing process. It doesn’t matter what technique you use, what does matter is that you’re very precise in how you approach the task.

“I will set the exhaust valve lash just as the intake valve for that cylinder is starting to close. I set the intake valve lash when the exhaust valve for that same cylinder is about halfway through its lift cycle. This is the best method to use because you are setting lash when the lifter is on the base circle of the cam,” Brad says.

The biggest thing that you should work on is being consistent with how you set valve lash. -Brad Rounds

Valve lash really isn’t that hard to set, but it’s also very easy to do incorrectly if you’re not careful. There are some common mistakes that you can avoid no matter if you’re a veteran at engine maintenance, or just learning how to do it the right way.

“You really want to be sure that you set the lash the same way each time and are paying attention to how you do it. People will set the lash when the lifter isn’t on the base circle of the cam, that’s something you really want to avoid doing. Racers won’t torque the locknut the same each time they lash valves and that’s going to cause problems. Another thing that will get you in trouble is not setting the lash at the same engine temperature each time…that will lead to all kinds of problems, too,” Brad explains.

When you set valve lash it's vital to do it the same each time.

If you follow a routine it’s easy to avoid these common mistakes when you’re setting valve lash on any engine. There are some best practices that you should use that will ensure you have good results.

“The biggest thing that you should work on is being consistent with how you set valve lash. Some people prefer a fair bit of drag on the feeler gauge; others prefer a very light load on the gauge when checking lash. Whichever you prefer, do it the same every time. The next thing you should work on is how precise you are when setting the lash. When turning the engine over to get to the next valve that needs to be set, make sure to take the time needed to get the valve you’re using as the key is very close to the same position for each cylinder. For example, when setting the exhaust lash, make sure that the intake valve comes back up to the same height after it gets to full lift,” Brad says.

Valve lash isn’t a “set it and forget it” type of thing — you have to check it regularly as a part of your engine maintenance program. When you take the time to set valve lash properly it will not only help your engine run its best, it will also make sure you catch any potentially catastrophic issues in advance.

Article Sources

About the author

Brian Wagner

Spending his childhood at different race tracks around Ohio with his family’s 1967 Nova, Brian developed a true love for drag racing. When Brian is not writing, you can find him at the track as a crew chief, doing freelance photography, or beating on his nitrous-fed 2000 Trans Am.
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