Setting valve lash isn’t hot rod voodoo. It’s not some sort of mechanical magic or wrenching witchcraft reserved for the automotive illuminati either.
So why do some people seem so spooked when you bring up the topic of adjusting valve lash?
Proper valve lash, which is the clearance between the rocker arm and valve tip in pushrod engines, is a critical way to reduce valvetrain wear and ensure optimum performance. Lash adjustments can also help you tune your engine for more low- or top-end horsepower, depending on the lash settings. With so many potential benefits, hot rodders should embrace the idea of adjusting valve lash—not fear it!
As our friends at COMP Cams explain perfectly in this video, there’s no need to shy away from making valve lash adjustments. The job can be done right in your home garage with the proper tools—valve lash adjusting wrench and feeler gauges—and the procedure shown below.
No hot rod hocus-pocus required.
“Valve lash is the mechanical clearance in the valvetrain from the valve tip to the rocker in a pushrod engine using solid lifters. Excessive lash will cause noise in the engine and wear in the valvetrain, while lashing the valve too tightly will cause the valve to hang open and the cylinder won’t run. Instead of making compression, air will blow through the valve—thus, proper valve lash is critical to optimum engine performance.
We use EOIC, which stands for ‘Exhaust Opening Intake Closing.’ This is just one method, but there are others. The EOIC method works with any pushrod engine using solid lifters.
With the valve covers and spark plugs removed, screw the poly-locks of the rocker arms until they just finger tight. Then, rotate the engine until the exhaust pushrod on the cylinder you are working on begins to move upward. You’ll be looking for any rocker arm movement. This is the process of exhaust opening. At this point, you can adjust the intake because the intake valve will be closed, ensuring that the intake lifter is on the base circle of the cam. This is particularly important as you run the risk of hanging open a valve if lash is adjusted when the lifter is not in this position. Place a feeler gauge between the valve tip and the rocker arm. Tighten the poly-lock of the rocker arm until the proper lash is found. When you get to your preferred lash, hold the adjuster nut in place and set it with the inner screw using an Allen wrench. The poly-lock adjuster nut adjusts the amount of valve lash while the set screw locks it into place. Finally, tighten with an adjustable torque wrench until it clicks at 20 foot-pounds of torque. This tightens the adjuster nut to the inner set screw and ensures that they do not come apart.
The lash on most engines is set anywhere from .012 inches to .022 inches. Check your cam card for exact valve lash settings.
To set lash on exhaust, rotate the engine again until you see the intake valve open to full lift and start to come back up. Again, simply watch for rocker arm movement. You then can set lash for exhaust the same way you did with your intake valve.
Some engine builders and racers use valve lash as a tool for tuning at the track. Tighter lash gives an engine more bottom end or torque, while greater lash creates more top end or horsepower, which is typically made in the higher rpm range. However, lashing a valve too tightly can hang open a valve while excessive lash will decrease duration of lift—in essence, making a cam smaller. Again, it is critically important to make sure that the lifter is on the base circle of the camshaft so that you can set lash. If you have lift, the lash will be incorrect and you can hang open a valve.”
How about one for us hydro lifter guys.
[…] Valve Lash You can also compensate for higher temperatures and altitude by adjusting valve lash. Increasing valve lash effectively shortens camshaft duration and decreases valve opening overlap. […]
[…] project, visit the Tools & Shop Equipment department on SummitRacing.com. Also, check out this video from COMP Cams—it takes you through the valve lash adjustment process step by […]
[…] Car Craft Magazine Now I can;t believe that both of these articles can be wrong and you be right. ( Lashing Out: How to Adjust Valve Lash – OnAllCylinders ) With the valve covers and spark plugs removed, screw the poly-locks of the rocker arms until they […]
tighter lash increases top end power , the article says the opposite. tighter lash = more duration & lift, the properties of a bigger camshaft
Yes the article is backwards.
Loose lash maks cam behave smaller making more bottom end power.
And vise versa..
That’s what I always thought!
But trying to understand the opposite, I figured that because at lower rpm it takes more time to fill the cylinder, the tighter lash gets the valve off the seat sooner which increases overlap which increases torque at low and mid rpm. BUT… at high rpm the increased overlap of tighter lash bleeds off some compression which decreases power. At high rpm the column of air in the intake has enough velocity that you don’t need that extra overlap to fill the cylinder. If you look at VE (volumetric efficiency) of an engine it’s always greater at high rpm. Sometimes more than 100% on a race/performance engine.
They did state at the end that if you go too far and have too much lash you will decrease overall duration and effectively make the cam look smaller, so reduce power.
Any other ideas?
One thing they omitted from this article is the feel of tightening the nut with the feeler gauge in place. You want to get to the point of just snug. And after setting with the screw and torquing the nut, you should be able to insert the feeler gauge back between valve and rocker with a little shove. If it goes in too easy lash is too loose. If it’s very hard or impossible to get back in then lash is too tight.
That’s really the only ‘magic’ to setting valve lash.
Another critique is the way they describe doing the adjustments one cylinder/valve at a time which would require you to spin the motor 16 times (for an 8 cyl). If you get a lash setting chart for your engine you can set lash for several valves at a time. This saves time when trying to make adjustments between rounds at the track or on a dyno.
And you will want a remote starter switch. Either one that clips to starter solenoid or if you’re doing adjustments often, a permanent one mounted in the engine compartment somewhere. Otherwise you’ll have to rotate the engine by hand.
You’ll only rotate the engine 1440 degrees if you go through the firing order. Also re: Volumetric efficiency will decrease with RPM as the cylinder has less time to fill.
If your cam is on the small side, tightening the lash will give a little duration and more high end. I the cam is correct for the application it won’t gain anything. Too tight can hit a piston or hang a valve open. If the cam is in the big side, loosening the lash will make the cam seem a little smaller and the valves can toss as well as the lifter bounce on the lobe if too loose. The best choice is the right cam as close as you can get to what you need. If you are having to change the lash more than .003 or .004 either way. a different cam is needed to prevent having to take the engine down and clean it up for a cam swap anyway. .003-.004 sure, but more than that is spanking your monkey.
If you have to much lash can you break a lifter or something?