DANGER - ALL COIL BIND IS BAD
Progressive springs do not make contact with each other..danger
Once assembled on the cylinder head a MINIMUM clearance OF .010"
should be used between EACH spring coil at minimum installed height ( max cam lift).
Reason to change Valve Springs
The reasons that a cam would require a change of valve springs are: 1. more valve lift than the OE spring can accommodate before coil bind. 2. A quicker valve opening and closing rate that requires more spring force to keep the valve from floating. Several other factors that dramatically affect valve spring choice are maximum RPM and valve weight. The force produced by the spring must control the kinetic energy of the valve. Kinetic energy is equal to mass times velocity squared. If you increase your rev limit by only 500 RPM, spring force at full lift must increase by approximately 10%. Usually the spring safety is 10% or slightly more but if you changed the cam and also increased the rev limit you may now have created a valve float problem. It is the same when you replace an OE titanium valve with a steel valve. The steel valve weighs 75% more than the titanium valve that the spring was designed for. Your spring must now be 75% stiffer or you must lower your rev limit by 15%!
The Valve Spring
A valve spring's job description is pretty cut and dry: It has to store energy so that the valve and its companion hardware can return to the seat. Sounds simple enough, and it is—until engine speeds increase. At higher rpm levels, a spring is taxed. This can eventually lead to valve float.
Most people envision valve float in a pushrod engine as the valve lifter physically parting company with the camshaft lobe. While that might (and often does) happen in severe situations, the first phase of the problem actually involves the valve bouncing off the seat. This bouncing action is virtually uncontrolled, and the end result is extended (and unintended) periods of valve overlap. Since the valves bounce open and closed during the compression stroke, horsepower is diluted by a dramatic margin. This rapid bouncing action (coupled with the invasion into the compression stroke) typically causes the engine to pop, bang and miss.
The valve springs perform the following functions;
Lifting the weight of the valve
Overcoming friction on the valve shaft when the valve closes Creating enough friction, or drag, to keep the valve train and valve following the camshaft profile accurately, by always providing (slightly) greater force than the inertial force of the accelerated mass of the valve. At the same time, the valve-spring forces must not be so large as to create excessive friction on the camshaft and potential loss of performance.
The sole purpose of the valve spring is to force the valve to follow the path of motion that is dictated by the camshaft lobe. Excessively stiff springs will steal torque from the engine and increase component wear while a spring that is not stiff enough will allow the valve to “float” or loose contact with the camshaft lobe. Valve float will eventually lead to component failure. The spring must also have enough available compression distance to allow the full amount of valve lift that is produced by the cam. Coil Bind is the term used to describe a condition of too little compression distance where the spring “bottoms out”. Coil bind will also lead to component failure. More on coil bind later..
The force required to keep the valve closed (for a length L1) is referred to as the preload force F1. The force required to maintain accurate camshaft tracking at high revs (for a length L2) is referred to as the spring force F2.
With regard to the dynamic behavior of a valve spring, it must be considered that they have a lower resonant frequency than other components, meaning that they can easily be stimulated to undergo resonant vibration. This means that the spring, in the presence of an appropriate stimulus, no longer follows the cam profile exactly, which leads to periodic excess tension and variations in the contact forces - including possible failure - and thereby results in a loss of function which leads to a loss of performance. In the worst case, the excess tension can lead to the spring breaking. It can, however, also be observed when there is no resonance, that at higher RPM, the springs do not follow the cam profile exactly. There are two main effects that must be considered. Firstly there is the additional lift past the cam (known as loft), which leads to excess tension and secondly there is the bounce after the down stroke of the cam pitch, which results in the valve reopening for a short period.
There are two options for examining the movement of the springs at different RPM. A laser can be used to record the movement of the valve, as this coincides with that of the spring. The second, more precise option is to measure the behavior of the springs using wire-resistance strain gauges affixed to the springs. The gauges change their resistance as they are stretched and relaxed during the oscillation of the springs. The changing resistance is recorded, making it possible to calculate the deformation of the material and therefore the motion of the springs. These methods allow us to design springs with smaller excess tensions, resulting in increased dependability and reduced performance losses.
Both procedures are used a Valve Train Dyno, which is able to spin at up to 15,000 rpm and which provides crucial information for optimal valve spring design and performance.
Because the resonant frequency is directly related to the spring rate and the mass of the spring, it is desirable to select as high a rate as possible, thereby increasing the resonant frequency, in order to avoid the occurrence of resonance within the engine´s working revolution range. Since, however, the limits of the stress range must be considered in designing the spring, in certain cases it is not possible to prevent the resonant frequency of the spring from falling within the working RPM range. There are many options for ensuring that the springs function correctly across the entire RPM range:
Shim the stock Spring
Stock springs float around 4500 rpm, on a stock cam, so it's pretty obvious they won't work with a performance camshaft. Back in the good old days, shade tree mechanics simply installed a handful of shims under the valve springs to increase pressure, but this lead to a host of other problems, which usually resulted in valve train failure.
Replace Stock spring with a stiffer one
It's much better to use a Single stiffer spring to avoid any possibility of coil bind. Single spring with a damper to reduce damaging harmonics in the valve train. The only drawback to using dampers, is that they usually require machining the valve spring seat.
The spring damper (if so equipped) is designed to absorb spring vibration. To oversimplify, spring vibration is much like a sound resonance traveling through the valve spring. If this resonance is timed just right, then the valve spring actually loses its effectiveness as a spring. Any time the actual spring is stiffened, then the natural resonance is increased. The spring damper counteracts this phenomenon. Dampers are not for street car use and are not used in production engines, typically because they produce friction and wear by design.
Typically, a damper will be constructed with flat sides. The sides of the damper fit tightly against the inner portion of the spring. As the valve spring goes through its motion, the damper actually rubs the side of the outer spring. In turn, it "damps" out the resonance or vibration (to a certain degree).
Damper failure is more common that we'd like to think—especially on high-lift, radical-profile camshafts. Occasionally, a damper will physically "unwind," and the lower portion of the assembly will work its way between two lower coils of the outer spring. Naturally, this stacks the spring into coil bind. When that happens, all kinds of carnage can occur if you don't catch the problem immediately. In most cases, selecting the correct length of damper will suffice, but if the problem plagues your application, it can be solved by slightly shortening the damper. Beyond this, and old racer trick is to glass-bead the damper after it's deburred and chamfered.Progressive springs
For progressive springs, the spring rate increases within the stress range, which also changes the resonant frequency. This means that the individual resonant frequencies are passed through for such a short period that no resonance occurs. However, because of fitting constraints, progressive set ups are not always possible.
Dual Springs with frictional damping
Inner and outer springs are used which rub together slightly, providing an engineered damping factor. If one of the two starts to resonate, the other damps out the motion before it can cause damage. This damping factor utilizes controlled friction, which can lead to a reduction in the life span of the springs. The inner spring in a dual-spring package can accomplish almost the same job as a damper. Typically, the inner spring will feature much lighter construction than the outer spring. Because of this, it vibrates or resonates at a much different (higher) rate than the outer spring. With different points of resonance or vibration for the inner and outer springs, then the ultimate RPM potential for the spring is increased over a single spring—even if the dual-spring package has identical open and seat pressures when compared to the single spring. Of course, this is seldom the case: In almost all applications, the added inner spring serves to increase both the open pressure and the seat pressure of the overall spring package.Dual Springs with Damper
A common combination is a dual spring with a damper. Essentially, the use of a damper with a dual spring allows the spring package to deliver more RPM without excessive spring pressure. However, the damper won't account for major gains over and above a common dual-spring setup without a damper. And where the dual valve spring is perfectly matched to the camshaft application, a damper isn't totally necessary. On the other hand, past experience has shown that a dual-spring package complete with a damper provides better spring life over the long haul. Given a choice (and if your application can accept it), use the dual-spring/damper combination.
Triple Springs
What about triple springs? For the most part, triples are best used in roller camshaft applications. They work very well in short bursts of extreme RPM, but in many mild applications, a run-of-the-mill double-spring/damper combination will work just as well. Furthermore, the design and construction of an optimized triple-spring package is totally another story in itself.
Why can't you just slide in the biggest available springs and be done with it? That'll work with a roller camshaft designed for drag racing only, but for use with a flat tappet camshaft of any sort (hydraulic or solid), too much spring can be worse than too little. Typically, a spring with anything more than 335 pounds of pressure on the nose (open pressure) will rapidly increase the wear on a flat tappet camshaft (along with wear in other areas such as cast-iron guides). Depending on the engine design, the cam profile and the valvetrain geometry, the practical limit for open pressure on a flat tappet cam is approximately 375 pounds. Any more and you'll probably be faced with a pile of broken camshaft pieces.
But there's more to the "too much is just right" scenario. If (and it's a big IF) the engine can physically live with a large amount of open spring pressure, you're still behind the 8 Ball. Why? Large amounts of valve spring pressure can eat horsepower. Increasing the open pressure by 50% also increases the amount of friction inside the engine. Simply stated, heavier springs require more horsepower to move the valvetrain. In the end, oil temperature increases and power levels can drop by five, six or more horsepower.
There are three primary spring shapes:
cylindrical
conical (tapered)
beehive (cylindrical with conical spring part on one side)
Both conical springs and beehive springs make it possible to reduce the masses being moved - on the one hand simply through the spring´s tapered shape and on the other through the smaller upper spring retainer, which again leads to an improvement in dynamics within the valve train. In comparison with conical springs, beehive springs offer the ability to operate with frictional damping for spring sets in the cylindrical parts of the inner/outer springs.
Myth- Too much spring pressure is hard on valves – In truth, what’s hard on valves is the speed at which they contact the valve seat when closing. What dictates how hard the valve hits the seat? It’s supposed to be the camshaft closing ramp (shape of the cam lobe), but when the spring pressures are too low, the valve does not follow it’s intended path and instead slams into the seat and actually bounces. Hence higher spring pressures can actually aid the valve by forcing it to more closely follow the shape of the cam lobe. On the other hand, to much pressure adds horsepower robbing friction. It also increases the wear and tear on valve spring components. IE: broken rocker arms and valve springs, bent push rods, worn valve guides, and so on. Therefore it is important to match the spring pressure to the profile of the camshaft. However you also need to take into consideration the intended RPM range of the motor. Basically... faster ramp speeds (more lift for a given duration), and/or higher rpm's, require increased spring pressures.
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Coil Bind myth -
Coil Bind is the term used to describe a condition of too little compression distance where the spring “bottoms out”. It also applies ANY TIME coils come in contact with each other during spring compression. It should be avoided at all costs. Contrary to common belief, progressive springs do not make contact with each other during compression.
Any spring installation should require you to examine the relationship between the inner spring and the damper to both the cylinder head seat and the valve spring retainer. Due to different designs in springs, retainers and spring seats, there might be coil bind at these locations, but no coil bind on the outer spring. Have a close look as the engine is turned through a cycle (by hand). In the case of a poorly selected spring (or spring retainer), don't be surprised if you see coil bind on the inner spring(s). If that's the case, you have to tear everything apart and install an inner spring that suits both the application and the spring retainer.
If you buzz the power plant on a regular basis and the engine goes into early valve float (or bounce), the spring material can actually become annealed by the heat buildup. The majority of valve springs are heat-tempered at 400 degrees during construction. Valve float can cause the spring to exceed that temperature by a significant margin. In most cases of valve float, the spring gets so hot that it glows red. This increased heat eventually kills the valve spring. This is magnified considerable when you have these hot coils making contact with each other during coil bind. This makes lubrication of the valve train critical but this is another discussion.
Once assembled on the cylinder head a MINIMUM clearance OF .010"
should be used between EACH spring coil at minimum installed height ( max cam lift).