Setting and adjusting the valve lash is often overlooked as a simplistic and unsophisticated task for proper engine maintenance, yet much can be gained by paying attention to valve lash. Good initial set up and keeping a close eye on the valve lash can alert you to a problem before it leads to a pernicious death of your powerplant. We checked with some of the industry’s top engine builders to find out what everyone should know about setting and adjusting valve lash.
About Our Experts
We wanted to know everything there was to know about setting valve lash so we contacted some of the most respected high performance engine builders whose combined experience in building top notch racing engines is over 110 years and whose resumes read like lifetime achievement members in the International Drag Racing Hall of Fame. These long-time engine builders are well known for their experience and engine knowledge, so we stacked the deck on this one to come up with the ultimate guide to setting valve lash. Lets take a look at our experts:
Scott Shafiroff has over thirty years of involvement in both racing and race engine building. Currently the owner of Shafiroff Race Engines and Components.
Pat Musi got into racing in 1969 and along the way became a eight-time Pro Street Champion with over 40 years of engine building experience. Owner of Pat Musi Performance.
David Reher started building engines with Buddy Morrison in 1971 in the back of an auto parts store in Mansfield, Texas. Master engine builder Reher leads the Reher-Morrison Racing Engines company and has for almost 40 years.
We also checked in with Ashley Newman, Technical Advisor at COMP Cams to get a manufacturer’s perspective on setting valve lash. Newman is also an accomplished circle track racer that understands the real world, “get ‘er dun” attitude of pit area maintenance as well as the maintenance in a laboratory type environment.
Understanding The Reason For Proper Valve Lash
Valve lash, which is the clearance between the tip of the rocker arm and valve stem tip, is a delicate balancing act between durability and maximum power. Most camshafts will come with a cam spec card that has a recommended valve lash setting. Scott Shafiroff explained, “Your cam card isn’t the number where your car will run the best, that’s just a starting place. Some cam companies publish a number on the cam card that is the minimum lash number, because if you run them any tighter than that, there’s no ramp or they run too rough. If you run them too loose though, it’s harder on the valve train. So there’s always a trade off between durability and power.”
Shafrioff continued to illustrate the point by saying, “If you can run the cam tighter and get the same performance, you’re better off as long as you haven’t gotten below the minimum lash. The looser you run it, the harder it is on the lifters. You’ve got to find that sweet spot where your car runs the best and back it off just a bit. That increases durability a lot and takes almost nothing away from the power. That’s the smart way to race.”
David Reher echoed the warning about checking your valve lash carefully. Too much gap between the rocker arm and valve stem can tear up a lifter. According to Reher, “A broken lifter is the most destructive component failure short of a broken connecting rod. Every time we overhaul a motor, we examine the used roller lifters very carefully. A simple act of preventive maintenance like routinely checking valve lash can save a racer a lot of money.”
Musi’s valve lash tricks start at the assembly of the valvetrain. “Making sure that there are no burrs in the lifter bore and the lifters turn in the bore” is critical in Musi’s book. “Just run a lifter bore hone through the bores to remove any nicks, burrs or corrosion,” he continued.
Regardless of what you’ve heard, there’s no mystery to setting valve lash on flat-tappet cams. Whether you’re dealing with hydraulic or mechanical flat tappet cams, we’ve got the procedure that will make this very important task as smooth as butter.
Starting with rocker arm installation, check to make sure that the pushrods have been installed through the guide plate into the center of the lifter. COMP Cam’s Ashley Newman recommends that “all pushrods be pre-oiled or primed, through the pushrod holes.”
Next, apply a small amount of assembly lube to both the valve stem tips and the rocker arm’s pushrod seats. We’ve had great success with COMP Cams assembly lube and it has become a staple in the powerTV garage. Once the valve stem tips and rocker arm seats are coated with assembly lube, the rocker arms can be installed on the rocker stud. Applying a generous amount of assembly lube to the rocker arm ball, position it on the rocker stud with the flat side of the trunnion facing up. Double-check to make sure that the pushrods are seated correctly in the lifters and the rocker arm seats. Using this exact process, install all the rocker arms. Newman told us, “It is extremely important to install the rocker arms without rotating the engine because you can accidentally bend a pushrod without knowing it.”
Install the adjusting nut by tighten the nut “finger tight” to the point where the pushrod has no lash, but will still spin with your fingers. Repeat this process until all pushrods are seated and all rocker arms are installed.
Finally, it’s time to set the valve lash. Our experts have told us that the best way they have found is to set the lash, one cylinder at a time, in the correct firing order. Make sure that the dampener bolt is installed in the crankshaft, turn the engine over by hand in the direction of its normal rotation.
For Hydraulic Lifter Camshafts
When the exhaust valve just begins to open on the first cylinder in the firing order, adjust the intake valve by loosening the adjusting nut slightly while spinning the pushrod until you feel lash in the rocker arm. Tighten the adjusting nut until the slack is taken out of the rocker arm and pushrod. Lightly turn the pushrod with your fingers as you tighten the adjusting nut, and you should feel a point where there is a little resistance (this is called Zero Lash). Turn the adjusting nut ½-turn past this point, giving you optimal pre-load for the rocker arm, pushrod and lifter. According to Newman, “you should look for .030-.060 of preload in a typical hydraulic Lifter.” Follow this procedure by carefully adjusting each intake valve according to cylinder firing order.
When all of the intake valves have been set to the proper valve lash, you can adjust the exhaust valves. Utilizing the same procedure as with the intake valves, you need to turn the engine over until the intake pushrod moves all the way up and rotates just past maximum lift. Now the exhaust valve can be adjusted. When all of the intake and exhaust valves have been set with the proper lash, it is common for all the top engine builders to perform a double check by rotating the engine and checking each valve again, starting from the first cylinder in the firing order.
Solid Lifter Camshafts
Solid lifter or mechanical camshaft valve lashing is set very similar to hydraulic lifter camshafts. Once again, the most important part is to remember to adjust just one valve on one cylinder at a time – starting with the first cylinder in the firing order and working your way through to the last cylinder.
The only difference in setting the lash on solid lifter camshafts is once you achieve zero lash, you adjust the intake valve by loosening the adjusting nut until you feel some lash on the rocker arm. Then you can set the lash on the valves by the specs listed in your camshaft spec card that came with the camshaft. Spin the intake rocker nut down with the correct thickness feeler gauge inserted between the valve stem and the tip of the rocker arm. Tighten the adjusting nut until there’s a slight drag when moving the feeler gauge. Do not over-tighten or you will risk damage to the camshaft in a short period of time.
Top Engine Builders give us 7 Tips for Setting Valve Lash:
Find the sweet spot. David Reher explained, “You’ve got to find that sweet spot where your car runs the best and back it off just a bit. That increases durability a lot and takes almost nothing away from the power.”
Set the valve lash “cold.” Scott Shafrioff reminded, “Cylinders heat up at different rates but cold is cold.” Shafrioff told us to set the valve lash with a cold engine and check the valve lash weekly with the engine at ambient air temperature. This will give you the best indication of when the lash is changing in one of the cylinders.
Ignore the “Chilton Manual” method of setting valve lash. Reher and Musi agree that this method only works for mild street camshafts. The best sequence to use when setting valve lash is to go by the firing order. This requires less turning of the crankshaft and will help ensure that valve overlap is not an issue.
EO/IC rule (Exhaust Opening and Intake Closing). Set the intake valve lash when the exhaust valve is beginning to open. This will put the intake lifter at the base circle which is where you want it to be. Then set the exhaust valve lash when the intake valve is about halfway down on the closing side.
Be Consistent. According to Musi, “Setting valve lash is not rocket science but you can help yourself by being consistent. Check the lash the same way every time otherwise it will be all over the place. You won’t know when you have a problem.”
Check valve lash weekly. David Reher says, “My number one rule of prevention is to never ignore a significant change in valve lash. If one valve suddenly has 20-thousandths more lash than the other valves, find out why. Is the valve bent, is the lifter broken, is the pushrod tip burned up? If you check the valve lash religiously, you can spot these problems before they cause further damage.”
Know what you are dealing with. If you are using trick aftermarket parts like aluminum blocks or titanium valves, follow the manufactures recommendations for maintenance like setting valve lash. The manufacture has already calculated the special compensations for these exotic materials.
Setting valve lash may be intimidating for the average Joe, but talking with top engine builders, valve lash is a simple and basic maintenance procedure that when done with a purpose, is a walk in the park. Finding the sweet spot, being consistent, and following a routine are keys in setting valve lash like a pro. Using these valve lash tips from our experts, you can amaze your family and friends and influence other gear heads with your newly found expertise. With this knowledge, you might become the fastest guy at the track. At bare minimum, you’ll be the fastest guy in the neighborhood, plus you’ll having bragging rights to having the most precise valve lash around. Either way, you earn bonus “cool” points with family and friends.