Q. Explain the process to achieve "controlled valve float". How to measure it. How to adjust it by machining the valve spring pockets. And how to measure and set the coil bind.

A. The term "Controlled Valve Float" gets thrown around constantly in the realm of Karting.  But what the heck is "Controlled Valve Float" anyway?  And why is it so important?

Let's start with the basics...

A 4 Cycle motor uses a rotating camshaft to raise and lower the intake and exhaust valves. The "profile" of the lobe determines the height and duration that the valves will be opened.  This is important, because the higher and longer that you can open the valves the greater the performance. The class that you race in determines actual physical limitations of the camshaft. For instance, in the stock classes, you are allowed a maximum lift of .233 inches on the camshaft lobes.  Right to start with, it appears as though you are limited in the amount of lift that the cam can create.  But we all know that there's a way around this physical limitation right?  It's called "Controlled Valve Float".  Because of the way that we engineered our cams, an interesting thing occurs when the motor reaches a certain rpm.  Normally, the valves ride on the surface of the lobe at all times, but with our Controlled Valve Float cams, the valve gets "thrown" higher than it's normal path and if all goes well, will land safely on the falling side of the lobe, producing noticeable increased HP!  How well the motor handles this task is determined by the motor's setup, particularly your spring setup.  Because while it is your camshaft that is throwing the valve, it is your spring's pressure that is "controlling" it, keeping the valve on it's intended path.

Read this next sentence, think about it, and then reread it.

The spring's pressure at installed height is the most crucial factor in configuring a proper controlled valve setup.

Side Note: Realistically you cannot rely on any set number for installed spring height. Why? Unfortunately no two springs have the exact same tension at a given height.  Using a suggested spring height without testing could produce mixed results, always use a proven measurement device when determining what the installed spring height should be.

Let's get started...

Things you'll need:

1. Spring Tester
For maximum HP, don't rely on a homemade fish scale reader, they're just not very accurate.  Two good products that come to mind are Intercomp's digital spring tester and Ez-Bore's Spring Tester.  (Both are great products, Their only drawbacks are they tend to be pricey.)
2. Controlled Valve Float capable cam (Model # depends on your application)
3. A good set of Springs (Again, your race class will determine what you are allowed to use). If your class allows, we stock the chrome silicon wire springs, they are very reliable as far as tension goes. These springs are extremely constant and resilient. 
3. Back Face Cutter Bit and Pilot
4. Block and Stop Gauge for cutter bit (Not required, but sure makes things easier) 
5. Standard Feeler Gauge (.170" works good) 

Procedure:

Fortunately, the math has been taken care of. For all of our stock cams we provide recommended spring pressures and coil bind figures (DynoCams Stock Profiles).  In our example we'll be using the 00-3 cam.  Recommended settings are:

Spring Pressure (Intake / Exhaust):   17lbs / 18lbs 
             Coil Bind (Intake / Exhaust):   .370   / .350

The spring pressures are the numbers we're concerned with, the coil bind numbers are what you would use to set spring height if you didn't have a spring tester. Let's use the spring tester to determine our spring height and see how close our estimated coil bind figures are.

1. Zero out the scale on the tester. Take the spring you will be using for the exhaust and position it in the center of the tester and crank the handle down until the spring bottoms out (coil bind). Reset your linear movement indicator (dial caliper) value to zero.  Now, loosen tension on the spring until you achieve a reading of 18 pounds. Read your linear movement indicator.  The value is the proper installed spring height.  Record the value and remove the spring.  Take the spring you will use for the intake side and repeat the above process to achieve a reading of 17 pounds. Record your results.

Scale calibration for the intake spring
Inset 1. Spring at Coil Bind, notice linear gauge set to zero Inset 2. Release the tension until weight indicator is at 18 Lbs  Inset 3. Linear reading at 18 Lbs. 



This installed spring height for this particular spring should be .376"

2. Now we'll need to modify the block to obtain the correct spring height. It will be necessary for the block to be recessed where the spring seats against the top of the block. There will ALWAYS be some amount of removal required to the block for this process so begin by using your back face cutter bit to remove just enough material to provide a smooth level surface for the spring to mate against the block. 


Back Face Cutter and pilot in position and ready to attach drill motor. 

3. Next we'll want to partially reassemble our motor to check the current spring height and to determine how much more material should be removed from the block. Insert the crank, valves, valve retainers, springs, lifters, and camshaft.  Take your feeler gauge and insert it between the lifter and valve you'll be measuring. Affix your dial indicator to the top of the block and position it on the valve that you will be measuring. Turn crank to position motor at top dead center, we want the valve that we're testing to be seated (at its lowest point).  Reset the dial indicator to zero. Now, turn the crank moving the valve up until the valve spring binds. 

(This picture shows feeler gauge between lifter and valve, also notice dial indicator at max lift.)

4.The reading from the dial indicator PLUS the actual height of the feeler gauge is your current installed spring height. In our example at this stage the dial indicator reads .146

.146 (actual reading) + .170 (feeler gauge height)= .316 (current installed spring height)

Therefore we need to face the block approximately .060 more
Record this value and repeat for the other valve

4.Disassemble the motor to allow for facing.  Reposition your facing bit and pilot as shown in step 2.  At this point you should use an adjustment block to properly calibrate the remaining stock to be removed. Adjust the stop to allow just under .070" to be removed (for our example). If you don't have the block and stop gauge to accurately set the amount of facing, remaining minute height adjustments can be made using a 300 grit sandpaper on the surface of the valve that mates the lifter shaft. Finally, reassemble your motor and go win a race!

Back Face Cutter shown with Block and Stop Gauge

Well, that's that.  We hope you've enjoyed this months installment of "The DynoCams Tech Question of the Month".  Join us next month as we delve into other mysteries of Karting issues.