By Dave Monyhan
Originally published in Engine Builder Magazine
Valve Spring: Almost all engines use valve springs to close the intake and exhaust valve during combustion cycles for internal or diesel combustion engines. Keep in mind the cam, pushrods, lifters, and rocker arms do all the work in opening these same valves, but it is the spring that closes and keeps that valve closed during the operation of the engine. These valve springs will be compressed and expanded over and over through their life cycle sometimes at more than 70,000 times in an hour for most high-performance engines, and over its life a valve spring could be compressed million, billions, or even trillion or more times during their life. Kind of like our current national dept. A valve spring also pushes back against all the other parts like the rocker arm, pushrod and lifter to maintain pressure on the cam lobe. Without valve springs, go fast engines, or any engine for that matter simply would not work. Well that statement may be argued by the fact that there is research going on as to having the valves completely eliminated and installing solenoids but we can discuss that in the future, so let’s stay on subject for now.
Valve Springs come in a (variety) cornucopia of sizes, configurations. Some are single springs with dampeners, others incorporate an inner spring and become a double spring, and then there is the extreme or the “Triple Spring.” Straight springs or beehive springs are also another choice.
Spring pressure is the key element to determine which spring should be used for what application. The camshaft design plays an all important role in determining which spring you need for that application. Lift is the critical spec or element when matching valve springs to the camshaft. The more lift you have the greater the pressure needs to be. The application of drag racing versus roundy-round or oval track racing also plays a role. Street car versus track only must be considered. I say that only because unlike a race car where we can and will change out valve spring at the end of every race, for a street application we want the long life so those springs must deliver the durability we need. Nobody wants to change out the valve springs on the Sunday Hot Rod every time we take the hot rod out for a ride. The quality of the valve spring you choose is also very important, broken valve springs are a nightmare for engine builders, because when the spring breaks, the valve drops, it hits the piston, and KA-BLUEY………….our oil pan is now a device for holding all the little fragments that just disintegrated themselves by that valve spring failing, and our race day is over, or our Sunday ride is now…….sitting by the side of the road waiting for the tow truck.
Springs not only come in different lengths and pressures they also come in different diameters. Generally speaking when you increase the spring pressure you will also increase the diameter of the valve spring itself. Now the cylinder head may not be machined for this increase in diameter so you will need to machine the spring seat to accommodate the larger spring. Fixed tooling is available to machine the spring seat, or you can also get an adjustable spring seat cutter to perform this operation right on your seat and guide machine.
Certain procedures are required for all applications of all valve springs, regardless of what you choose for your particular application. All valves springs need to be measured for specific opened and closed heights. All valve spring need to be confirmed that the pressure is what the manufacture says it is. And all High performance valve springs should be pre-cycled prior to being installed on the cylinder head.
I read a really cool article about “spring cycling” a method in which you “cycle” the valve springs to full coil bind several times so as to “break in” these high performance springs prior to final pressure testing, and measuring before installing them into the cylinder head. The claimed that they were able to measure almost 10 pounds of lost spring seat pressure by following this spring cycling procedure resulting in more accurate installed heights, that will result in less pressure loss when the engine is ran at its racing RPM range.
This cycling process is only for brand new high-performance springs and is not needed for the plain old stock or grocery getter type of applications. I also spoke to Joe Mondello and he stated that he cycles all of his race springs and then he also takes it one step further, by submitting them to a cycle of stress relieving, followed by a cycle of cryogenics freezing. You can learn more about Joe’s procedure here.
Measure, measure, measure!
Free length: this measurement is the first one you need to make. Free length is measured by placing the springs in a row, separating intake from exhaust if they are different (if they are rotator caps then they will be of different lengths) and measuring the overall length with no pressure being applied. If the variation is more than .025” the spring should be tossed. Next inspect your spring closely to ensure the top and bottom are parallel and that they are square. Also line them all in a row to check overall height with a straight edge. You can use a square to ensure the spring is straight by placing the spring on a flat surface and placing the square vertically next to the spring. Make sure the spring is square top to bottom and straight to with-in .062”.
Installed Height: This closed pressure is critical due to the fact that the spring must close and seal against vacuum and pressure. Weak spring pressures can allow the valve to bounce off the valve seat and this will cause a loss of power and excessive seat and valve wear. Closed valve spring pressure should be within 5 to 10 pounds of each other to be serviceable or approximately 10% from weakest to strongest measurement.
Open Valve Spring: This pressure must be enough to keep the lifter in contact with the camshaft during high RPMs. The valve must also maintain contact with the rocker arm and the rocker arm to the pushrod and the pushrod to the lifter and the lifter to the camshaft; if any of these clearances increase you will have engine failure.
Shims, VSIs, or Spring Washers are all the same thing with different names. These shims are used on mostly stock applications to increase the pressures, and are available in .015″, .030″ and .060″ thicknesses. They come in regular steel and hardened steel for high-performance applications. They allow you to fine tune the closed and open valve spring pressures to achieve correct installed height. If you find the need to shim past .060″………….replace that stock valve spring.
After you have laid out the springs and checked the free length, find the spec sheet you received with your new valve springs, or look up the spec in the manuals if you are re-using valve springs.
As with any component, you need to write everything down on the work order. Open height, Installed height, pressures at both settings and overall length. This way you have a paper trail to reference when it comes time to freshen up a race motor or in the event of failure. Probably the most important factor in selecting a valve spring is: Correct seat pressure, open pressure, and spring rate for the camshaft you are using.
Analog versus Digital
Now we all have a spring tester or tester in our shop right? Of course you do. But which type of tester do you have? Some models come only as a analog style of measuring pressure and height, and others in recent times have evolved to digital readouts for pressure down to the 1/10th of a pound, height can now be measured in .001″ (thousandths of an inch), choosing which spring tester is your first challenge to determine which type is best for you and your customers. I will start with the unit we all grew up with….the analog style of spring tester.
These units have been the backbone of the engine building trade for many years. They are fast, pretty accurate, and very easy to use. They are subject to the eye of the beholder. You have to insure you are looking correctly at the dial on the face to make sure pressure is read correctly and you have to look correctly at the measuring scale to insure your height is right. These units have an option to upgrade the measuring height to either a dial indicator or a digital readout. I highly recommend the digital readout to measure specific height. No options to upgrade the analog pressure dial, so calibration is very critical to insure your pressure is correct.
Whichever machine you have is the one you are going to use, so I am not here to tell you which to buy or say one is better than the other, but if you are shopping or in the mood to upgrade to a new machine, then I say check them all out. Contact your favorite shop supply company and compare the features and benefits. Find out what is, what isn’t, and who is going to be there for re-calibration, technical support before you buy, then select the machine that is best suited for you and your customers needs.
See ya in the shop!