Arturbo

I want to hear what you guys think "vavle float" is. So the question is, how do you define valve float? I am curious to see what people think it is.

art

TurBoTeG

Any time when the valve isnt in sequence with the rest of the roating assembly i consider valve float. Its when the spring cant pull the valve back quick enough due to not having enough tension on the spring

twkdCD595

I would say it is when the engine is revving so fast the valves remain open... this is because the valvetrain components can't maintain thier synchronous contact.

from what I understand.

Arturbo

Keep them coming.

art

Wo-Nelly

Because all mechanical things have a resonate frequency, when both the valve and valve springs operate at the same frequency, the valve spring will lose it's effecientcy and surge. hence the reason for dual springs

Unsung

From my understanding, although I am a complete idiot, valve float happens when the cam is rolling off the valve after lift, and the cam removes itself quicker than the valve can follow due to lack of spring stiffness, and the valve whacks the back of the rocker. Like I said, even if the smartest person (in this case Luke) tries to explain it to me, I'm usually wrong when I repeat it back.

Mista Bone

Valve float = when the valvesprings cannot close the valves quick enough to meet the cam profile.

Valve BOUNCE is a whole different story!

Arturbo

Nice!! somebody added valve bounce.

ZoRG

Simple.... it is something that happens only in high rpm engines, also it is not neccesarily due to the springs not being stiff enough, it also has to do with the valvetrain weight. the lighter the valves/springs/rockers etc, the less spring pressure will be needed to stop valves from floating. It is overall more beneficial to reduce valvetrain weight than to use stiffer springs...

Mista Bone

I would have said "valve flutter" but that would have cause massive confusion,

genop

This may have nothing to do with it, but I have heard people talking about valves "stretching" at very high rpms causing then to hit the top of the piston and we all know what happens after that....I don't even know if this really happens though since I dont rev my little sohc past the rev limit.........

genop

also, what exactly is valve bounce? Someone mentioned it but didnt really explain.

Short Round

to solve valve flutter, use a valve BOV y0

genop

are you serious? How would that help. Please explain.

dasher

he's joking... hey, a BOV stops compression surge flutter, why not Valve flutter?

genop

yea, I thought he was joking. Just wanted to make sure

951

good thread, id like to know what the actual answer is, im assuming arturbo knows...but from what i understand(not much) is that the valve springs dont have enough potential/kinetic energy to slap the valves open/closed as fast as the cam is telling them too.

b18bturbo

A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components. The onset of valve float prevents higher-rpm operation. Extended periods of valve float will damage the valvetrain which leads to piston destruction.

It simple concept if you think about it

951

but, what is constituted as a "high rpm engine situation"? does the change from safe operating RPM, to unstable(high) RPMS occur immediately? or determined by weight of the valve train, stiffness of the springs?

twkdCD595

why is it that alot of people think they are gonna drop the valve also when valve float occurs? I have not had much experience firsthand with this.

SiRkid

ive always thought of it as.
when the engine spins at x rpm and the spring cannot keep up and the valve remains open and or contacts the piston.(this is just what ive come to learn by word of mouth/some reading..never really researched it)

so whats the actual definition?

DaX

iTrader: (1)

when the follower looses contact with the cam.

for more cool stuff like this,

click the "CAM DYNAMICS ESSAY" link in the bottom of my sig...

JonnyCoupe

Force = mass x acceleration

Work the rest out yourself

earl

I think Mista Bone nailed it but I have a follow up question for Art (no fair asking Larry) and everyone else, of course.

When is valve float a good thing and why do certain engine builders go out of their way to cause it to happen to their motor?

SoulSurfer

I've heard of controlled valve float. From what I remember it's used when certain class regulations limit the amount of lift a cam can have. With controlled valve float the valve is thrown a little bit higher than normal and lands on the other side of the lobe. I guess this "acts" as a higher profile cam and increases power. Am I way off, Earl?