TECHNICAL TIPS

WMR SERVICE BULLETIN 05 (Sept 28, 2006)

FOUR STROKE VALVE SPRINGS - CONICAL SPRING TECHNOLOGY

WMR Competition Performance has been testing and developing four stroke engine components for several years. We have introduced many new products into the market such as one piece titanium and stainless steel valves, high compression pistons, valve buckets, replacement valve seats, manual cam chain tensioners and Dual Valve Springs. All of these products have been designed to improve performance and extend engine life.

One common design challenge for all four strokes is valve train life. It has become evident that small bore four strokes have very vulnerable valves systems. Partly because of the high RPM's and excessive heat. Most valves trains will experience problems early in the motors life.

At WMR our focus has always been performance, we look at all parts of a motor to see where improvements can be made. One of the first things we looked at was valve springs. Improper spring performance hinders motor performance and can cause valve and seat damage. This condition is commonly known as "valve float" The traditional cure for valve float has been to add spring pressure, in an attempt to harness out of control valves, increasing pressure is not a guarantee that the spring will be able to control the valve. There is a very delicate balance between the perfect pressure and too much pressure. Adding to much valve spring pressure in an attempt to stop valve float can add unwanted friction and heat to an already hot running motor.

After thousands of hours on the track and Dyno testing various springs and pressures, it became very clear that the real problem was SPRING SURGE or spring harmonics. All springs have a propensity to vibrate at a certain frequency. The higher the RPM's the more likely the vibration. The less mass a motor has, the more damaging the vibrations can be. The principle factors affecting the frequency of the vibrations on a spring are the springs mass and its stiffness. When a spring is exposed to a damaging frequency as the motors rpm's increase, the vibration will rapidly build up to such an extent that the spring will no longer be able to control its own motion. So the question is, how do you keep valve spring pressure low enough while at the same time controlling valve surge and harmonics? One answer has been the use of Dual Springs. With the dual spring there is an outer and inner spring each having a distinctly different resonant frequency because of the coil and wire size. The two springs rub together during opening and closing to dampen and counter unwanted spring vibration, this is intended to deaden the vibrations and eliminate the harmonics. This concept works to a certain extent and sounds good, however the two springs rubbing together will generate excessive unwanted friction, drag and heat.

Spring surge was the driving force behind the adoption of air springs (pneumatic springs) on the 19000 rpm Formula One race engines. Formula One used Conical springs for a few years until they developed the pneumatic systems. The problem with small bore four stroke dirt bikes is, that it's not currently feasible to install air springs. If we want to come up with the perfect valve spring for the four stroke single cylinder motocross bike, then the primary goal is to find a way of eliminating surge (harmonics) without introducing destructive friction damping into the equation.

WMR has found a solution to this question, we have designed a Conical shaped spring. Using super clean valve spring quality wire that has been Eddy Current tested to eliminate impurities, our new Conical Valve Springs are the answer for the single cylinder cast aluminum, high revving four stroke motors.

HOW WMR CONICAL SPRINGS WORK

We have talked about how proper valve spring design stops the spring from vibrating and harmonizing. If not stopped, the spring will surge and be unable to recover to its designed pressure at a specific installed height. WMR has found the best way to do this is to design a spring that has different size coils at each winding,  that way the coils can not vibrate at the same resonant frequency. That is how the WMR Conical Spring is designed. The reason a conventional spring harmonizes is because every coil is the same size and for the most part equally spaced. A conventional spring is the perfect environment for the vibrations to become amplified, causing the spring to act as if it were sacked out. To demonstrate this, next time you start your bike, stand to the side and rev up the motor. You will see the seat squat down from the shock spring surging. This is the same thing that happens to your valve springs, they vibrate and squat down to the point that they no longer have the pressure needed to close the valve.

It is important to understand how critical it is for the spring to keep the cam lobe in contact with the valve at all times. If the springs are squatting or surging, they will be unable to recover to their designed closed pressure, this will leave the valve floating above the seat as the cam falls away from the valve. The combustion cycle will then slam the valve shut with thousands of times more pressure than the valve was designed to handle. Remember the valve is intended to be gently set onto the seat by the cam not slammed into the seat by combustion. If the valve is set gently onto the seat, then the seat is able to pull heat out of the valve head keeping the valves heat range at acceptable levels. If the valve is "floating" it never really gets enough time on the seat because it is bouncing vigorously before it is lifted again by the cam. If a valve does not have the ability to dissipate heat it will continue to get hotter and eventually start to deteriorate. After examining thousands of worn out KX250 and 450F’s, RMZ250 and 450’s,YZF250 and 450’s and CRF250 and 450 valve trains, it is obvious that the valves were floating and being beaten into the seats. The faster more aggressive rider will see problems earlier than a rider that shifts more often and keeps the motor in the lower RPM ranges, however every rider will eventually rev the bike and cause the stock springs to surge. Each time this happens, the valves will experience accelerated wear and can eventually fail.

There has been much talk about why it seems to always be the intake valves that have the premature failure. Keep in mind that the force causing the valve failure is happening during the combustion cycle, at that point the exhaust valves are already closed and not affected by the combustion. The intake valves are supposed to be closed also however because they are floating they are negatively affected by the unwanted forces. Exhaust valves experience more heat that can affect the guides and seats but typically exhaust valves last much longer than intakes.

With conventionally wound springs the coil size and spacing are all equal, the spring designer has little control over the springs open or over the nose pressure because he is most likely designing the spring for a desired closed pressure. For example a spring with a designed closed pressure of 28 pounds will have an open pressure of over 100 pounds. There is no control over the open pressure because all the coils are the same size. A valve spring will experience float at the lower end of the pressure range and rarely requires more pressure over the nose. It is beneficial to have the pressure as low as possible to allow the motor to rev easier and experience less unwanted forces witch act against its ability to be efficient.

With WMR Conical Valve springs we are able to control the open and closed pressures because of the spring’s unique design. A Conical spring with a closed pressure of 32 pounds can de designed to have an open pressure as low as 88 pounds. A conventional spring at 32 pounds would have an open pressure over 105 pounds. Any time you can lessen spring pressures you are helping the motor run better and be more efficient.

The way a Conical Spring operates is somewhat different from that of a conventional spring. On Conical Springs the coils become progressively smaller from base to top. As with any spring, given a particular wire size, the smaller the coil the stiffer the spring becomes. Because of this, a conical springs top coils are not only smaller and lighter but also stiffer.

While working the bigger coils at the bottom, being less stiff, compress before those at the top. As the spring is compressed during opening of the valve the bottom coils progressively settle down onto the one below. Soon as each part of the coil has settled on the neighboring coil beneath, it is removed from the effective valve mass equation as far as mass in motion and spring weight are concerned.

By the time a valve controlled by a Conical Spring reaches full lift, only the small top coils are actually being moved and the spring’s stiffness has escalated considerably. In basic terms this means that at full lift the effective spring mass is a little less than 10% of the springs total mass. That is 10% as compared to 30% of a conventional spring. So with Conical Springs, a typical 100 gram spring reacts in the valve train as if it were 10 grams. This savings can be as much as the equivalent of a steel valve versus a titanium valve.

Now this all sounds pretty good, but it gets better. Since the top coil is smaller you can use a  smaller and lighter retainer. That means, the over the nose weight savings of a Conical Spring is substantial. At 13000rpm's even a feather on the top of a valve would feel heavy.

I have tried to explain in simple terms how WMR's new Conical Valve Springs can eliminate spring surge, and valve train mass, but I cant stress enough how important that is to your engine and valve train life, especially in a single cylinder 250cc & 450cc motocross bike that is constantly operating at different loads and RPM's. The fact that a single cylinder lightweight MX motor is built for maximum strength at minimum weight actually works against eliminating unwanted resonant frequencies, there is very little mass in the motor to help combat against vibration. As the rpm's increase so does the potential for harmonics and valve spring failure. We believe the stock springs have been the cause of many of the heating issues as well as the valve train failures.

We are very excited about our Conical Valve Springs. They have proven they will reduce heat and friction, and control the fragile valve trains in all brands of four strokes. WMR makes Conical Valve Springs for Honda, Suzuki, Kawasaki, Yamaha, and KTM. You can call the shop to learn more @ 1-866-WMR-RACE

Continue to the second part of this bulletin - "Why They Work"

WMR - WITH EXPERIENCE COMES POWER

PREVIOUS SERVICE BULLETINS:

1. Plug Cap for new four stroke KAWASAKI & SUZUKI KX250F& RMZ250F

2. Air Box Ring

3. Four Stroke Valve Springs - Conical Spring Technology

4. KX250F & RM-Z250 Cam Seizing

Check out our web site at www.wmr1.com for all your Motocross performance needs.

WE BUILD THE BEST RACE EQUIPMENT,
WINNING IS UP TO YOU.

1-866-WMR-RACE
(866-967-7223)
(772) 426-3000 local