Adjusting the valves in an engine seems to be a simple chore. And it can be simple with plenty of practice, but adjusting valve lash (or clearance) without experience and patience can be frustrating. It can also be less than accurate.
Types Of Adjustment
Let's look at the different types of adjusting mechanisms that you might encounter. First are the valves that cannot be adjusted, including those on some Fords with rockers that look like those on a Chevy but are bolted solid. The intent is for the hydraulic lifters to take up any clearance. When that's the case, valve lash can only be adjusted by using aftermarket parts that allow adjustment.
The common Chevrolet adjustable rocker uses a pivot ball. This rocker can pivot any direction. Its side angle or tilt is located by the pushrod and the valve. Adjustment is performed by tightening or loosening a pinch-type locknut-one that has been pinched together slightly on one end. This makes it tight enough that it will stay where it's put.
The trouble with this arrangement is that after being removed and replaced a few times, the pinch is stretched and the nut becomes loose. This can allow the valve lash adjustment to change. Be aware, however, that plastic insert locknuts will fail from heat.
There are several solutions. One is to throw away the nuts after three or four adjustments and/or each removal from the stud. I have a large collection. Many years ago, I would re-pinch the locknuts with a hammer and a punch. I won't bore you with stories about what I messed up by doing this.
Another solution-and a better one, I might add-is to use what are commonly called poly locks. These are hardened nuts that are several times longer than standard nuts. One end is screwed onto the rocker stud and adjusts the rocker's lash setting. A set screw is then threaded into the other end and tightened down against the stud. This locks the nut to the stud by wedging the threads. It takes some patience to do this and get the lash setting you want. When the set screw is tightened, it often moves the nut and/or pulls against the threads, so you have to do this several times to get it right.
Another thing you might encounter is the adjustable pushrod, which is made mostly in the aftermarket for applications in which the engine did not originally have any adjustment. They adjust with a screw on end and a nut for locking.
There are also some rocker arms that have an adjusting screw on one end. Here the adjusting screw usually has a screwdriver slot so it can be turned. The nut then locks the screw in place.
How To Adjust
It would be simple to insert the appropriate feeler gauge between the valve and rocker, then tighten the adjuster to it. But that's easier said than done. Feeler gauges are thin strips of metal, usually in a set, of an exact thickness. They get their name from being used as a feeler between two parts. If the gauge feels loose between the valve and rocker, then clearance is looser than its thickness. If the gauge is tight and can't be easily moved between the valve and rocker, then clearance will be too tight. With a little experience, you will develop a feel for where the gauge can be moved without having slack in its movement.
I have used a technique with two feeler gauge strips. If the desired adjustment is 0.020 inch, select one gauge of 0.019 inch and another of 0.021 inch. When the larger drags hard going in and the thinner one slides easily, you have it right. This method is less dependent on feel and might be easier for someone learning the skills. However, with experience, using the single gauge of the correct thickness will be faster.
What Lash Setting Do You Really Want?The first setting a racer should be concerned with is the one recommended by the cam grinder. Let's begin with hydraulic lifter cams. Many mechanics working with stock application vehicles make a preliminary adjustment to get the engine running. Then they allow the lifter to pump up with the engine running and tighten the adjustment just until the rattle stops, then turn the adjuster one more full round. This is not only quieter, but gives the lifter some internal movement that compensates for wear. Racers often do it another way. When rules call for the use of hydraulic lifters, other methods of adjustment can slightly increase performance. Hydraulic lifters need oil pressure to work. Setting them can be done with the engine on or off. Spin the oil pump to pressurize the lifter.
What you want is zero lash, which takes full advantage of the cam's lift. Because there is no feeler gauge that is zero thickness, other means must be used to achieve this setting. Don't substitute hydraulics for solid lifters because the hydraulic lifter will leak down slightly or not hold against valvespring pressure.
To get zero lash with the engine off, the lifter must be pressurized. Do this by spinning the oil pump with a driver, usually a drill or air ratchet. Twirl the pushrod with your fingers until the adjuster tightens it. Stop there.
I have used this method with the engine running when adjusting hydraulics. It can be used on any engine using a threaded rocker stud. When using stock Chevy 1.5 rockers (actually somewhere around 1.46:1 ratio), I can set the clearance, engine running, at 0.016 inch. Then by turning the hex adjusting nut one flat, I am at zero lash. When you have other rocker arm ratios such as a true 1.5:1 or a 1.6:1, you will need to establish the measurement for your ratio.
I did this by sacrificing an old pushrod. I cut off several inches on one end and then welded on a washer to keep it in place. Now the pushrod has a solid stop that is not dependent on the lifter. I set the lash to 0.005 inch, backed the adjuster nut off exactly one flat, and checked the lash, which read 0.021 inch. Note the difference (0.016 inch, in my case) between the two measurements. Now set the lash to this distance (0.016). Turn the adjuster nut one flat to achieve zero lash. Do this several times to make sure you're getting the correct measurement. Remove the test pushrod. Then set all of your valves to your established measurement and turn each adjuster nut one flat.
Setting the lash with solid lifters only requires the lash to be set with the recommended feeler gauge. The engine need not be running nor have oil pressure pumped up.
Many solid lifters look like hydraulics. These have an insert with a snap ring. To be sure that you have a solid lifter, use a soft tool and press on the lifter insert. If it compresses, it is hydraulic; if it doesn't move, it is a solid.
When setting lash on engines with used stock rocker arms, you should check the condition of the face of the rocker that contacts the valve. This face often has a groove worn by the valve. With this groove present, the feeler gauge will give you false readings. Additionally, if the rockers have been removed and re-installed in locations other than the original on the same head, the grooves won't align with the valves. This means the valve stem will be cutting a new groove in an already used rocker arm.
Aftermarket full roller or roller tip rocker arms have a roller bearing where the tip contacts the valve stem. Using these prevents a groove from being worn in the rocker. There can also be a reduction in friction, especially with strong racing valvesprings.
The aftermarket rockers are often used with a stud girdle. This usually consists of two parallel bars above the rockers that clamp around long adjuster nuts. The effect is minimized flex and stabilized rocker studs, resulting in the valve movement more closely following the cam design. With a stud girdle, the lash may change when it is tightened and loosened. This happens when the rocker studs are not in perfect alignment. So loosen the girdle, set the lash on the valves, and re-tighten the girdle. Then go back and check the lash. If any lash settings are more than 0.002 inch off from before, loosen the girdle and adjust to the variance.
I spoke at length with Mark Campbell, Crane Cams' director of camshaft and valvetrain research and development. He feels that one can spend too much time trying to get the lash setting to perfect accuracy, and that one or two thousandths doesn't make a real difference. We also discussed using lash setting to change cam characteristics. For instance, tightening the lash will advance the cam. Mark said this is an acceptable practice as long as the adjustment doesn't vary more than 0.007 inch from the original specs. If more adjustment than that increases performance, then a cam change is in order.
When To Set The Valve Lash
Set the lash when the cam lobes are pointed away from the lifters. In the absence of a clear glass engine block, we have to rely on the timing pointer on the crank balancer. There are other methods, but they all give a similar result. When the timing pointer points to top dead center (TDC) on the number one cylinder and both valves are closed, the cam lobes are pointing away from the lifter. Set both the intake and exhaust valve lash to the cam specifications.
Next follow the firing order sequence to find the next cylinder. It is a big help if the balancer is marked in 90-degree increments. If it is not, get a timing tape that goes on the balancer. After having found the number one cylinder's position, rotate the crank in the direction the engine runs to the next 90 degree mark. The second cylinder in the firing order will be in position to be adjusted. Do this through two complete rotations of the crank, setting the lash on a cylinder, each 90 degrees marked.
Bumping the engine over with the starter and trying to hit the marks can lead to frustration and the utterance of some ugly words. Try removing the plugs and using a long handle ratchet to turn the engine with the balancer bolt. If there is too much in the way to reach the bolt, such as a fan shroud, then try this: Put a V-belt around a crank pulley or the balancer. Tape it securely to a tube or strong stick. When pulled in the direction of rotation, it will tighten like a pipe wrench. Any way you do it, getting the cam lobe high point position away from the lifter is necessary to set the lash properly.
Use whatever method of adjustment is necessary for your engine type. Stock pinch nuts wear out quickly and stock rockers can have a groove that inhibits proper adjustments. Aftermarket roller rockers are good. Mark your balancer or wrap it with a timing tape for proper orientation. When using a stud girdle, re-check after tightening the girdle. Finally, get some practice and it will get easier with time.
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