redtail2426

iTrader: (10)

Okay something that doesnt exactly make sense to me,or needs to be explained.I completely understand how an exhaust valve can hit,the piston is on its way up and the exhaust valve is hung open to long because the lifter either rides over the top of the cam lobe and catches some air time keeping the valve open to long and causing it to hit the piston.BUT,the intake valve starts opening when the piston is at the top and then chases the piston down the bore,then closes after the piston goes past Bdc,and starts its way back up.The only way i can see it hitting is if its held open REALLY long or bounces back open when the piston is almost up all the way.So if you can fill me in please do.And when people float the valves what exactly is happening.I have heard a few different things.Valves bouncing and lifters flying,so which is it,or is it both

vettenuts

iTrader: (4)

Intake is likely opening before TDC. Valve float is loss of control, so yes they can bounce and remain open at the wrong times. Basically float means the lifter is no longer following the cam lobe contour due to loss of control by the valve springs.

redtail2426

iTrader: (10)

okay,the intake opens before tdc,yes but how does it hit.I mean if you over rev or are cutting clearances close,what would make it open even earlier then it should

santacruzx

I just took my LS1 apart, every exhaust valve touched a piston and made a mark. Probably an over-rev missed shift. Strangely enough, the heads are fine and the intakes didn't hit at all.

ShevrolayZ28

iTrader: (4)

Imagine losing control of the heavier and much larger intake valve so badly that it never really closes. The cam spins so fast that the valve springs cannot close the valve before the cam lobe comes back around again. The valve "floats". Meanwhile, the piston is making it's full stroke.

redtail2426

iTrader: (10)

okay an answer thanks.thats some serious floatage.yeah i can see how that can happen with some of the larger intake valves.