How To Set Valve Lash

(Prototype/Jeff Smith)

The designers of late model engines similar the GM LS, Ford Modular engine, and the Chrysler Gen 3 Hemi accept in many ways made it easy for performance enthusiasts.

Not the least of which is the internet lash organisation where the engine builder doesn't have to run through setting hydraulic lifter preload on all 16 valves.

In a internet lash system, a set distance betwixt the lifter (on the cam lobe'southward base circle) and the rocker arm creates the preload on the lifter based on pushrod length. To set the preload, all that's necessary is to torque the bolts down on the rocker arm. It's that simple.

This is not the example with older engines like small- and large-block Chevys and Fords. These engines and many others require adjusting either the preload on the hydraulic lifter, or setting mechanical cam lash (clearance) for each individual valve.

In prehistoric times, tuners ready lash or preload with the valve cover removed and the engine running — creating an oil-flinging mess. There'due south a much cleaner, more efficient way to accomplish this with the engine not running.

Let's showtime by reviewing why lash is needed on mechanical cams and preload is necessary for hydraulic lifters.

Mechanical camshafts, both flat tappet and rollers, crave clearance between the cam lobe and the follower. Older camshafts were designed with much wider clearances than modernistic camshafts. For example, the original 302 c.i.d. Z-28 engines used a mechanical flat tappet camshaft that required 0.030-inch of clearance when the engine was hot. Current performance mechanical rollers have reduced that effigy to as little as 0.010- to 0.12-inch.

Hydraulic lifters operate differently. These use a small piston inside the lifter body supported by a short column of oil. The lifter is designed to exist preloaded or compressed for a given amount. This creates a brusk cavalcade of pressurized oil underneath the piston that automatically compensates for expansion as the engine reaches operating temperature. This column of oil maintains the proper valve opening and closing human relationship throughout the entire engine temperature operating range. That is not the case with mechanical camshafts where the lash will change when the engine is common cold compared to at normal operating temperature.

There are actually several procedures for adjusting lash with the engine not running, but we'll show y'all the ane that is easiest to remember.

This procedure does not require you to memorize the engine'southward firing gild. The originator of this idea is lost to history, only he was probably a cam designer or a racer who was interested in a elementary process that's easy to execute.

The of import part of setting lash or preload is to ensure the lifter y'all will be working with is on the base circle of the lobe. This is very important. We'll use a big-block Chevy for this sit-in. While nosotros're using this particular engine, this process tin can exist used on any 4-stroke internal combustion engine because they all operate the same style.

We call this procedure Exhaust Opening-Intake Closing (EO-IC). If you turn the engine over slowly clockwise, watch the valves as they operate. When the exhaust valve begins to open, this places the intake lifter on the same cylinder on the base circle of the intake lobe. This allows you lot to ready the lash or preload on the intake lobe.

Then if you plough the engine roughly 1½ revolutions, the intake valve will begin its lift cycle. When the intake rocker is more halfway down the closing side, this will place the exhaust valve on its base circle so that it can be set up.

If you're not sure of the intake or exhaust valve, a unproblematic way to do that is to line upwards the frazzle port with its valve. This is sometimes easier than tracing the intake port. If you find the exhaust valve, the other valve with be the intake.

We'll run through ane cylinder on our large-block to evidence how this works.

With the engine not running and the valve covers off, we like to get-go with the Number One cylinder which is, in this case, the leading cylinder on the driver side. If the engine is in the car, you tin can crash-land the engine over with the starter motor. Of course, y'all can besides turn the engine over using the creepo commodities.

The procedure starts by turning the engine and watching for the frazzle valve to open. Once the exhaust valve begins to open (EO), we can now move over to set up the preload on the intake valve for that cylinder. Our detail big-block is running a hydraulic flat tappet camshaft, so we volition want to set roughly a one-half-turn of preload into the lifter.

Permit's assume we're setting the preload for the first time. With the rocker arm loose, tighten the adjuster on the rocker stud while feeling clearance with the rocker arm and there's no tension on the pushrod. You can also twirl or spin the pushrod with your fingers on your left manus as you tighten the rocker stud adjuster with your right. If this is a brand new engine, nosotros like to perform this lash adjustment before we install the intake manifold so we can sentry the cup in the lifter to see exactly when zilch lash is achieved. If the engine is fully assembled, pay close attention to when pushrod clearance is eliminated. This is aught lash.

To set up preload, just tighten the adjuster nut another half-turn after zero lash. If yous are setting the lash on a mechanical lifter camshaft, use the appropriate feeler judge between the valve tip and the rocker arm and adjust the lash until there is a reasonable tug or pull on the feeler judge. With both the intake and frazzle valves set on this cylinder, we can motility downwardly the line to each side by side cylinder. I adopt to do 1 cylinder at a time in sequence. This minimizes mistakes from overlooking a pair of valves.

1 variable is the question of the amount of preload. For decades, older engines required a preload of three-quarters to 1 full turn of the adjuster. After, the performance manufacture evolved to a reduced setting of quarter-plow. If we read the COMP instruction however, they recommend a three-quarter or ane full turn much like the OE'south.

I fashion to decide the actual amount of preload is by the thread count on the rocker stud. For example a 7/xvi-inch rocker stud uses a fine thread which is twenty threads per inch. This means one full plough on the adjuster nut is worth 0.050-inch. Once null lash is determined, a half-turn of the adjuster nut volition depress the lifter piston 0.025-inch. A full plow will produce 0.050-inch.

It's across the scope of this story to dive into a full investigation into hydraulic lifter preload hither. Let'due south but say that one full turn of preload by and large tends to amend operation on hydraulic lifter engines. The reason for this is that the greater preload pushes the internal piston closer to the bottom of its travel. This reduces the volume of oil underneath the piston.

This minimizes the amount of air entrained in the oil that will let the piston to compress.

Remember, a liquid cannot be compressed while air is easily squeezed. Past reducing the volume under the lifter piston, this creates a situation where the lifter acts more than similar a solid lifter — which is a good thing. Of course, this assumes that the valvetrain will remain stable at loftier rpm and not feel valve bladder.

If valvetrain separation occurs (due to loss of control or valve float), the lifter piston volition instantly push upward, concur the valve open up and the engine loses big power. Then lifter preload is a double-edged sword. With this short explanation, at least you empathize all the related factors.

By following this elementary process to setting valves on an independent rocker stud style engine, you can at present quickly gear up the valves without having to look upwards reference materials, setting sequences, or memorize a firing society.

Just remember Exhaust Open up – Intake Endmost – EO – IC and you're halfway to completing the project.

Start by removing the valve cover and exist able to easily plough the engine over either with the starter motor or by hand with a socket and ratchet on the crankshaft. Yous volition also need the proper wrenches to adjust the rockers. Poly locks will require a wrench for the adjuster and an Allen wrench for the lock. (Image/Jeff Smith)

When we refer to the base circle, information technology references the concentric portion of the lobe (the bottom portion). This is the zero lift point which is the standard reference position for setting lifter preload or lash. (Prototype/Jeff Smith)

With the exhaust rocker (foreground) just beginning to open, this places the intake lobe on the base circumvolve and allows us to set the intake preload by finding zero lash and calculation ¾-plow. (Image/Jeff Smith)

Setting preload on some hydraulic lifter can be tricky because the piston may depress very easily. Equally you tighten the adjuster, approach zero lash by twirling the pushrod with your fingers to plant naught lash. This is important. (Image/Jeff Smith)

With the intake preload set, rotate the engine until the intake valve runs is on the closing side. Stop when the intake is by and large closed and at present yous can adjust preload on the exhaust side. (Epitome/Jeff Smith)

Setting lash on a mechanical roller cam is accomplished using the same EO-IC procedure except that you volition add in the required hot clearance. Almost current technology cams are somewhere between 0.010- and 0.020-inch of clearance with the engine at normal operating temperature.

Author: Jeff Smith Jeff Smith has had a passion for cars since he began working at his grandfather'south gas station at the historic period 10. Later on graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod mag before returning to his beginning love of writing technical stories. Since 2003, Jeff has held diverse positions at Automobile Craft (including editor), has written books on minor block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves equally a regular contributor to OnAllCylinders.

Source: https://www.onallcylinders.com/2020/06/25/the-basics-of-setting-and-adjusting-valve-lash/

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