Re: Wanna see valve float in action?
I did a little research and this is probably the bes explaination I found
""Valve float" is really valve train separation. All of the various components of the valve train (lifters, pushrods, rockers, valves, etc) are designed to move as a single entity, following the cams profile with all the components "held together" by constant spring pressure.
To produce maximum power, it would be desirable to bang the valves wide open almost instantaneously at the right moment, and slam them shut equally quickly when required. In the real world that won't work, because the valve train components cannot withstand those physical stresses. To cushion these violent forces, there are "lash ramps" (mechanical cams) or "acceleration/deceleration ramps" (hydraulic cams) that begin the acceleration of the valve off the seat more gently, and also set it back down on the seat more gently. Once accelerating, the cam ramp speed increases in a progressive fashion to achieve a lot of movement in a little distance (lift under the curve).
As the cam follower approaches the nose of the cam, it must decelerate, stop, and start down the other side of the cam lobe. The valve spring pressure works against the inertia created by the speeding mass of all the valve train components. As long as valve spring pressure is greater than component inertia, the valve train components track the profile of the cam lobe, stopping, starting, accelerating and decelerating in proper fashion.
The problem comes when the speed of the valve train components becomes great enough that the inertia created is stronger than the valve spring pressure. Then, as the cam follower approaches the nose of the cam, the spring is unable to stop the motion in the opening direction, and the cam follower is "launched" right off the nose of the cam. Kinda' like flinging mud off of a stick.
With no cam pressure now pushing on the cam follower, the spring finally "catches up" and overcomes the opening inertia, and starts to close the valve train again. The problem is, the cam lobe has continued to turn and now the lifter will be accelerated violently closed by the valve spring until it slams back into the cam lobe at some point, causing severe shocks throughout the valve train, excessive wear, and often breakage. The valve usually bounces off the side of the lobe once or more, keeping it out of proper contact with the lobe. If the cam follower is "out of control" or bouncing in the air as the valve approaches the seat, the cam cannot set the valve gently back on the seat with the deceleration ramp. Instead, the valve slams hard into the seat, and bounces again.
So, you get valve train separation typically at two points...over the nose of the cam, and setting the valve back onto the seat. The valve spring SEAT pressure must be adequate to maintain integrity of valve train motion as it approaches the closed position (to prevent valve bounce off the seat). The valve spring OPEN pressure must be adequate to control the valve train deceleration over the nose of the cam. That's why it's important to use a spring with proper pressure specs at both points.
Valve train separation and the resulting "bouncing" introduces unnatural, high frequency undulations or harmonics into the valve springs, and will eventually cause breakage of springs, throwing of valve spring retainer keepers, or just plain allow a valve to crash into a piston....any of which spoils your day.
Spring pressure required to avoid valve train separation is dependent on several factors, including peak rpm required, weight of all the valve train components (and therefore inertia), acceleration and deceleration rates of the cam ramps, and even proper rocker arm geometry to avoid side loading and frictional resistance from the valve guides. Bottom line, listen to your cam manufacturer on spring recommendations. They get paid to do all those calculations, and they can do it better than we can by the seat of our pants.
We all know that unnecessarily heavy valve springs rob horsepower and increase wear; however, too weak springs almost always eventually result in breakage. Saved horsepower doesn't help when it won't run anymore. Don't let 'em "float!""
Basically, if you are experiencing this, your going to end up breaking stuff alot faster then normal since your slamming the valves back in place and such. For "e" cars, this is something that can happen when you start revving past the stock redline since they have a single valve spring setup. I cars can run higher since they have the dual springs and have the ability to overcome the forces the valves place on them and keep them in contact with the cam lobes at all times instead of launching them off. Besides, if you watch the vids, you can see how the valves are wobbling and such, I can imagine that is just not good.....
Hope that helps! VALVE FLOAT......NO BUENO!!!!