TECHNICAL TIPS

WMR SERVICE BULLETIN 005.1 (Sept 28, 2006)

CONICAL VALVE SPRINGS - MORE INFO ABOUT WHY THEY WORK

In service bulletin 005 we began to explain how  WMR Conical Valve Springs work, the following information will explain Why they work!

Let’s talk about spring Surge or Harmonics. As we stated before spring surge begins at different points for any given spring, depending on the springs mass and stiffness. The stiffness is determined by the type and size of wire and the size of the coils. For example at a given wire size, a small diameter coil is stiffer than a large diameter coil and each size coil will have a different resonant frequency.  In simple terms each size coil will vibrate at a different point. Each time the cam lobe strikes the top of the valve a vibration is sent through spring downward and then back up. As the wire vibrates it losses its natural ability to recover and return to its original position.

Now imagine the vibrations caused when the spring is being struck about 200 times every second plus add the vibration caused by the rest of the motor, the spring will end up vibrating out of control. When this happens, the valve will float and cause loss of power as well as excessive heat and wear. We call this problem Valve Float. Sometimes the valve head may even strike the piston and send more unwanted vibrations through the valve train, piston and to the crankshaft.

With a conventional valve spring, each coil is the same diameter, as the spring compresses, it moves all the coils together proportionately from the top to the bottom. All coils are in motion at all times, this adds to the effective valve mass (we will discuss this further below) Since all the coils are the same size, they all have the same resonant frequency therefore they will all vibrate together and will actually "harmonize" with each other amplifying the negative effect of the vibration. That's why it is called spring" Harmonics". If you have ever played a guitar you know that if you place your finger against a vibrating string you will deaden the vibration. With a conventional valve spring all the coils are free to vibrate and there is no way to stop them .One way to stop the unwanted vibration is to deaden the wire with contact from an outside force like your finger does with the guitar string. The most common way to do this has been with a Dual Spring. Dual springs consist of two constant wound springs one inside the other. Each spring has different size wire and therefore a different resonant frequency.

The inside spring is meant to rub against the outside spring and deaden the vibration. This works pretty well at reasonable rpm's but looses some effect as the rpm's increase. The main problem with this kind of spring is the excessive friction and heat generated as they rub together as well as the extra weight from the two springs. This can cause more problems in the motor than the original harmonics did.

With the new WMR Conical Springs everything I have just told you about the conventional spring changes. First since the coils at the bottom are bigger and get smaller as they go up, the bottom of the spring compress first. As the bottom coils compress they settle onto each other and deaden themselves. Now with a conventional spring this would be called coil bind and is not a good thing, but with the WMR Conical Spring it is a very good thing. The spring is not coil bound because the top coils are still in play. The bottom coils have been deadened from vibration and have also been removed from the effective valve mass.

Notice the size difference of a conical spring (on left) compared to a dual spring. Conical spring is 32% lighter.

It may be hard to see in this photo, but notice how the bottom coils have compressed and been removed from the effective mass of the spring, leaving the smaller lighter coils on top to do the work. The entire spring is used to eliminate surge.

A heavy effective valve mass is a valve trains biggest enemy, motor builders are always looking for ways to lessen effective valve mass because by doing so they will eliminate stress on the motor. Less pressure means more power, rpm's and torque, less heat and longer engine life.

It has long been conventional wisdom to increase spring pressure to lessen valve surge. This works to a certain extent, because as the springs mass and stiffness go up so does its ability to resist vibration The only problem is the stiffer the spring the more stress on the motor. Also if you were to make a conventional spring stiff enough to stop all harmonics at 13000 rpm's it would be too stiff for the valves, seats, cams, cam chain, buckets etc. The effect could ultimately be worse than the original surging valves.

It is easy to build a low revving four stroke motor such as a lawn mower, because you can run very light valve spring pressures and balance all the forces so they work together. The problem we have with the new high performance four stroke motocross bikes is we need high rpms, good horse power, torque and light engine weight. All of these things work against the old way of thinking when it comes to valve springs.

In Formula One the best engineers in the world have been working on these issues for a long time, the concept of a conical spring was born in F1 and was working very well until they invented air driven valves.

F1 motors are revving over 19000rpm's for long periods of time and engineers needed to remove valve spring surge from the equation. They were able to do that very effectively with Conical springs. With our light weight MX bikes air springs may be a long way down the road but WMR Conical Springs are here now. At 13000rpm's the conical spring will do a super job of eliminating valve spring surge and help lengthen the life of our valve trains.

Because the spring is working more effectively and because we no longer need to increase pressure to combat harmonics, we are able to use a smaller wire size and open up the coils. This result is a lighter spring creating less effective valve spring mass. Can you imagine the forces that develop from the valve opening and closing? Just like Newton's law of motion states "An object in motion stays in motion until an equal and opposite force acts upon it" In other words, The cam is pushing on a valve in motion trying to change its direction hundreds of times a second. The heavier the effective valve mass the harder it is to change directions, heat and pressure will increase. That is why it is so important to get the "over the nose pressure"  and the valve train weight down as low as possible.

Remember how the top coils of the WMR Conical Springs are smaller than the bottom ones? The smaller top coils are the only ones in play at full lift and because they are smaller they are lighter. Also because the bigger bottom coils are less stiff, they have already compressed and are no longer in play. This result is the effective mass of a conical spring is reduced to about 10% of the spring’s original mass. This is in sharp contrast to a conventional spring that sees about 30% of its original  mass. When you combine the Conical spring’s lighter weight with the greatly reduced effective mass it's easy to see how beneficial the Conical design is.

The last piece of the puzzle is the retainers and keepers. If you can reduce the weight of these items you can further improve the entire system. Because the top coil is smaller than a conventionally wound coils, the retainer can be smaller. WMR offers lighter Titanium retainers for Honda, Suzuki, Kawasaki and Yamaha.

WMR Competition Performance has risen to the top as the Premier Four Stroke Motocross Race Shop on the East Coast. We offer everything for Motocross such as full bike services, modified motors and suspension, parts and accessories, riding gear, pit bikes and more. Our full machine shop specializes in head work, installing bronze seats and guides as well as repairing damaged heads and making custom components that improve the performance and handling of your machine...

We are very excited about the Conical Spring technology and are proud to be at the fore front of its development in the motocross market.

You can call and talk to a technician at 1-866-WMR-RACE toll free if you have any more questions, our visit our web site at www.wmr1.com for frequent updates.

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WMR - WITH EXPERIENCE COMES POWER

PREVIOUS SERVICE BULLETINS:

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

2. 2004 Kawasaki & Suzuki KX250F & RMZ250F

3. Air Box Ring (Coming Soon!)

4. Ignition Cover Plugs (Coming Soon!)

5. Four Stroke Valve Springs - Conical Spring Technology

6. KX250F & RM-Z250 Cam Seizing

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

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