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.