Valve Lash 101


Drag Race 101: What’s Best for your Small Block Chevy

Part X; Lashing Out—Solid-Lifter Valve Lash Adjustments for Power

To the uneducated, adjusting the valve lash of a solid-lifter camshaft seems like an unsophisticated task of simple maintenance. But, there is a lot of information—and power, to be gained by paying attention to the lashing of your valves. For instance, properly setting the lash, and keeping a watchful eye can not only affect power, but can give early warning to a problem before it leads to a more serious issue.

Simply put, valve lash, is the clearance that is measured between the tip of the rocker arm, and tip of the valve stem. Properly setting this lash has a direct correlation not only with power, but also durability. Solid-lifter camshafts will come with a cam card that lists a recommended valve-lash setting. But, while the camshaft manufacturer’s recommendations are a safe setting, the number on the cam card might not be the number where your engine runs at its best. Some manufacturers even publish a “minimum” number on the cam card that is the minimum amount of acceptable lash. If you run the lash any tighter than that, performance—and durability could be severely hampered. Conversely, if you run the lash too loose, it’s even harder on the valve train. So, how do you know what your lash should be?

Many engine builders believe that if you tighten the lash—and get the same performance as when it is a little looser, you’re better off. This is as long as your lash setting isn’t below the minimum lash requirement. What you need to do is to find the right setting where your engine runs its best. Once you find that setting, then back the lash off just a bit (.002 – .005 inch). Doing this increases durability, and takes almost nothing away from the power that you have found.

There is no magic formula to setting valve lash on solid-lifter camshafts. Every engine will like something different. The best way to set the lash is to set one cylinder at a time. To set proper valve lash requires that each lifter be on the base circle of the camshaft to ensure the valve is completely closed when you adjust the rocker arm. Many “gurus” have “shortcut” methods for setting lash, but the most foolproof method is to remember EO/IC. This stands for exhaust opening/intake closing. With the valve covers removed, turn over the engine. While doing this, keep your eye on the exhaust valve. When the exhaust valve starts to open, stop turning the engine, and adjust the lash on that cylinder’s intake valve. Then, turn the engine over again, keeping your eye on the intake valve of the same cylinder. When the intake valve is fully open, and the rocker tip is at the bottom of its travel, continue to turn the engine over until the valve is about 2/3 of the way closed. Stop and adjust the exhaust valve on that cylinder. Repeat on each of the remaining cylinders.

To get the proper lash, the feeler gauge should pass the “go/no-go” test. This means that if .020-inch lash is what you want, a .020-inch feeler gauge will slide through, but a .021-inch gauge will not. The time at which you set your lash also has a dramatic affect on performance. Your engine is made of metals. Metal expands and contracts with hot and cold conditions. Camshaft manufacturers list there lash settings as a hot number, this means that each cylinder should be checked with the engine oil around 200 degrees. The problem is, how fast do you think the engine starts to cool when it stops running? Because of this, some enthusiasts will set the lash of one cylinder while the engine is hot, and then let the engine completely cool to ambient temperature. Once the engine cools, they can now get a setting of lash in a cold state. Since the engine temperature isn’t constantly changing while it is ambient, a more “stable” lash setting can be achieved.

But, what affect does lash have on an engine’s performance? By changing the lash, you can effectively alter the camshaft’s profile—albeit a small amount. Let’s take for example, that your engine has a cam with .500-inch valve lift. If you set the lash at .020-inch, it actually only opens the valve a total of .480 inch (the first .020 inch of movement is used to take up the lash). Now, tighten the lash to .010 inch, and the valve then opens .490 inch. Tightening the lash also has a small affect on duration, as it increases slightly as the lash is tightened. This is because less clearance means that the valve opens earlier and closes later as the lifter rides on the cam lobe.

Let’s think about a few preset conditions for a particular valve lash. At a particular setting, the valve event has a certain amount of degrees of duration that begins when the valve starts to move off its seat, goes thru the length of duration, and then returns to the valve seat. If you increase the lash, the experienced duration gets shorter, and you lose valve lift by about the same rate. This is of course subject to the rocker-arm ratio at the valve. In this instance, the engine’s low-end torque would increase, but the peak realization of horsepower will occur at a lower rpm point. If you tighten the lash, this has the opposite effect, as your realized torque will be decreased, and your horsepower will be achieved at a higher rpm.

So, while it is proven that adjustments in valve lash can affect the torque and power of your engine, is it really enough of an affect to make it worthwhile. That depends on your perspective. Some guys feel that adjusting the lash while at the track can help their launch by moving the realized torque of the engine. If you have time to make those adjustments, it might be worthwhile. But, if you feel that you have to make changes in your valve lash to gain power or torque—depending on the situation, maybe what you really need to look into, is getting a better camshaft for your application.

Using the EO/IC method of adjusting lash is the best way to accomplish the task. EO/IC stands for exhaust opening/intake closing. When the exhaust valve starts to open, adjust the lash on that cylinder’s intake valve. Next, when the intake valve is fully open, and the rocker tip is at the bottom of its travel, turn the engine over until the valve is about 2/3 of the way closed. Stop and adjust the exhaust valve on that cylinder. Repeat on each of the remaining cylinders.

You will need the proper tolls to adjust the lash. While a standard wrench and a set of feeler gauges will do, a rocker arm adjusting wrench is a luxury that when you finally use, you’ll wonder how you did without.

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