Has The Science Changed Over The Years?

Valve lash. In certain engines, it’s a requirement to smooth-running performance. In others, it could indicate a problem. In case you didn’t know, valve lash is the “gap” measured between the rocker arm and valve. It creates a ticking noise that can either be a hint to an engine packing a few extra ponies under the hood, or an engine that needs some serious maintenance. The telltale tick of a solid-lifter cam is not the same as the “lifter noise” of a valvetrain out of adjustment.

When it comes to actually setting valves, there is no shortage of opinions about completing the task, and that includes misinformation. We wanted to be sure to deliver you guys the right information, so we reached out to Mark Campbell, Sales Director at COMP Cams. Mark has been with the company for several years and knows more than a thing or two about camshafts and valvetrains. But, before we get into the do’s and don’ts of adjusting valves, we should probably cover a few basics for you new guys.

setting valves

To keep it simple; a solid lifter (right) is as its name implies, one piece of metal. There are no internal components like there are in a hydraulic lifter (left).

To Oil Or Not To Oil

First off, a valve lifter (also called a tappet or cam follower) rides on the lobe of the camshaft. It then transfers the lifter’s up-and-down motion to open and close the valves. Also, when discussing lifters, you are either referring to a hydraulic or solid unit. A hydraulic lifter has a spring-loaded internal allowing for variations in operation by compressing and releasing the lifter’s internals. This is required for proper engine function (more on that later).

From the factory, most domestic V8 engines were equipped with hydraulic lifters. These “oil-filled” lifters are designed to accommodate variations in valvetrain clearance in order to continuously maintain zero lash under all operating conditions. This is accomplished by the filling and emptying of the lifter with engine oil through a metering orifice and a check valve. When the lifter is filling with oil, it is pumping up. When the oil is exiting the lifter, it is bleeding-off (leaking down).

A solid-lifter on the other hand, does not fill with oil. Unlike a hydraulic lifter which has a spring-loaded mechanism inside, a solid lifter has no moving internal mechanism to take up clearance, and in fact, requires a small amount of clearance be inserted between the lifter, pushrod, and rocker arm to operate properly. A solid lifter does not have the “give” of a spring-loaded internal mechanism and requires clearance to allow for those variations that occur during operation. This clearance is called the valve lash.

Generically speaking, the tried-and-true method of eliminating all clearance and then giving the adjuster a 1/4- or 1/2-turn works okay, but you should really be setting the preload specific to the lifter type, valve spring pressure, intended RPM range, and cam profile.” – Mark Campbell

But, when setting valves, why does a solid lifter require lash? As the cam rotates, the lifter must allow the valve to close. With a spring-filled hydraulic lifter, the internal spring compensates for the high-revving action of the moving components, and the lifter’s movement of the internal spring allows the valve to close and fully seat. Since a solid lifter does not have the ability to compress, some clearance must be entered into the system to allow the valve to fully close (seat). Theoretically, this should occur at zero lash, but with the introduction of heat while the engine is running, some additional clearance is needed to give the solid-lifter valvetrain a little room to compensate for dimensional changes due to heat expansion.

setting valves

A specified amount of clearance must be set when using solid lifters. If no clearance is utilized, not only will the engine not run correctly—especially after getting warm—but damage to the valvetrain could occur.

As mentioned, a solid lifter requires a predetermined amount of lash, while an engine with a hydraulic cam requires zero lash. In reality, when adjusting the valves on an engine using hydraulic lifters, some might call the process setting lash, but you are not actually setting the lash or clearance – you’re actually setting the preload on the lifter’s internal mechanism.

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To understand how the hydraulic lifter is able to accommodate valvetrain slack while maintaining zero lash, we should look at its inner workings. When the valve is closed, the plunger spring in the hydraulic lifter takes up all clearance in the valvetrain. At this time, oil enters the lifter body through feed holes, and flows inside to the lifter’s plunger. The oil continues to flow down through the hole in the bottom of the plunger, around the check valve, and through the holes in the check-valve retainer to completely fill the cavity below.

setting valves

As the lifter begins to ride up the cam lobe, the oil below the plunger tries to escape past the check valve. This sudden flow of oil forces the check valve to seat, which seals the hole at the bottom of the plunger. At this time, the full load of the valvetrain is being applied on the lifter. But, since fluid cannot be compressed, the lifter now acts as if it is a solid design.

In a mild to slightly modified engine, hydraulic-valve lifters offers several advantages over a solid lifter. Some of these are: no need for frequent valve adjustments, quieter operation since there is no lash, increased valve and camshaft life, smoother engine operation, and the continuous ability to compensate for expansion and contraction of the valvetrain parts due to temperature change.

Getting It Right

If you ask four different people about adjusting valve lash or preload, you’ll likely get three to four different instructions about how to do it.

“When setting valves, some still think that using the TDC method is okay with a performance camshaft,” said Mark. “It can work in some cases, but using the intake closed/exhaust open method is 100-percent foolproof.” The TDC-method Mark referenced is the old-school train of thought to position the piston at top dead center (TDC). Once the piston was at TDC, you would then adjust both valves for that cylinder. However, as Mark stated, current thinking finds this to be the incorrect procedure to obtain the proper lash—especially in engines with an aggressive camshaft profile.

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We asked Mark if there were any misconceptions about adjusting hydraulic-lifter preload. “Generically speaking, the tried-and-true method of eliminating all clearance and then giving the adjuster a 1/4- or 1/2-turn works okay, but you should really be setting the preload specific to the lifter type, valve spring pressure, intended RPM range, and cam profile. This takes more knowledge of the whole combination, and can net much better results for the given application.

“For example, a high RPM, high spring-pressure application with a hydraulic-roller lifter should have a short-travel lifter to start, but also have the preload set to the bottom third of the lifter travel. This will reduce the plunger travel and increase the lifter’s ability to recover when it may run out of control. Effectively, by setting the lifter like that, it is turning more into a solid lifter (with a small amount of cushion), so no lash is required like a solid. This is how we achieve 9,000 rpm in an LS engine with a hydraulic roller. This is in conjunction with our new lobe-profile technology, conical valve-spring package, and new rocker arm technology.”

Setting preload on hydraulic lifters is done by tightening the rocker arm nut while twisting the pushrod until it feels snug. It’s a little easier with the intake manifold off the engine.

Turning Wrenches

The best way to adjust preload on a hydraulic lifter, is to first have the engine at operating temperature. Adjusting an engine that is not “warmed-up” should only be done on new engines as a preliminary adjustment while on the engine stand. After a new engine has been started and the initial break-in procedures complete, re-adjust the valves with it at operating temperature.

“Work on one cylinder at a time,” says Mark. “Setting the intake valve and the exhaust valve for one cylinder at a time is ultimately the best way, and works no matter the engine or the camshaft. Set the intake valve when the exhaust valve just starts to open. Set the exhaust valve after the intake fully opens and is about halfway closed. This is how we recommend setting valves on any engine, and is foolproof.”

setting valves

Exploded view of hydraulic lifter.

Begin by spinning the pushrod and feeling for resistance while tightening the rocker-arm nut. Once a small amount of resistance is felt, this is considered zero lash. Next, turn the wrench 1/8- to 1/4-turn (if this is a performance, racing, or other high-RPM-use engine). For a mild street engine, turn the wrench 1/4- to 1/2-turn after zero lash is achieved. Continue this procedure through all the intake valves and then start on the exhaust valves.

Setting valves with solid lifters is similar to hydraulic-lifter adjustments, however, instead of feeling for resistance while spinning the pushrod, you will be using a feeler gauge to verify the lash setting (clearance) between the rocker arm and valve. Remember, with a solid lifter, you need clearance, not preload. Again, the engine should be at operating temperature. Again, Mark recommends working on one cylinder at a time.

The cam card that came with your camshaft will tell you the lash setting to achieve. Typically, the lash setting will be slightly larger on the exhaust than the intake. As an example, if your card specifies a valve lash setting of .022-inch, place the appropriate feeler gauge between the top of the valve stem and the rocker arm tip. Then, snug the rocker-arm nut until you begin to feel resistance. You should still be able to slide the feeler gauge back and forth. Remember, this is a lash setting and should not be overly tight.

setting valves

When the lifter is filling with oil through the feed hole (arrow), it is pumping up. Oil then travels through the lifter and then through the push rod to the rocker arm.

“The lash required is really determined by the lobe design and the application,” Mark stated. “We have solid-roller lobe designs that have as low as .005- to .007-inch lash, and some with up to .028-inch or more. A typical street or endurance application with a solid roller will typically have tighter lash, and a race engine might have a bit more lash. The trend is certainly towards utilizing a tighter lash, as it has shown to be easier overall on valvetrain parts. Also, a customer can adjust the lash on a camshaft +/- a few thousands of an inch to effectively move the cam timing a bit to see if there are any gains to be had with a particular grind.”

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If you have installed a new camshaft, the engine will obviously be cold, but you still need to set the valves. A problem arises at this time, because the lash specifications on your cam card call for an engine that is at normal operating temperature. When this is the case, take the setting provided on the cam card, and adjust as follows: with an iron block and iron heads, add .002-inch to the lash. If you are using an iron block and aluminum heads, subtract .006-inch.

setting valves

By increasing or decreasing the gap between the rocker arm and valve, you can move the powerband of the engine. Just be careful to adjust the gap minimally.

Adjusting Lash For Increased Performance

When setting valves while adjusting the lash on a solid-lifter, some performance gains can be had by adjusting the amount of lash. Since the valves cannot move until the clearance (valve lash) is eliminated, reducing the amount of lash, will cause the valve to open slightly sooner. Although minimal, this will provide slightly more lift. This will make the camshaft appear to be larger to the engine, due to this slight increase in duration and lift.

If you increase the amount of lash, the opposite occurs. The valve will open later, providing slightly less lift. These adjustments should be minimal (start with 0.001- to 0.003-inch). By reducing the lash, top-end horsepower will show a slight increase. Increasing the lash can improve bottom-end torque and therefore, acceleration.

“How you set the lash is the most important,” Mark affirmed. “Having an engine at a consistent temperature—as close to the operating temperature at which the engine will be run—and the method used to set the lash are the most important. Again, the proper method is to do one cylinder at a time, and to set the intake valve as the exhaust valve just starts to open. Then, set the exhaust valve as the intake has opened all the way and is about half way closed. This method will work on a farm tractor, Pro Stock engine, and everything in between.”

setting valves

If you are not using pushrod guide-plates, self-aligning rocker arms are a great choice. But if used in a solid-lifter application, then a feeler gauge will need to be trimmed to fit between the guide washers.

Hopefully, this simple tutorial into adjusting the valves of your engine can eliminate some of the myths and misconceptions that surround this seemingly easy maintenance task. Now it’s time for you to go reset your valves and enjoy that hot rod sitting in your garage.



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