Valve Float

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dibbons

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When a hydraulic lifter cammed motor experiences valve float, how far open are the valves when this happens?

Do both intake and exhaust valves float at the same time or do the heavier intake valves always float first?

When does this condition cause contact between the piston dome and valve face? Thank you.
 
Weight of the valve components and mostly worn out springs are the cause of float. Since the intake weighs more, than yes it is the one that will float first.
 
When a hydraulic lifter cammed motor experiences valve float, how far open are the valves when this happens? Valve float can occur with any conventional valve train, ie hydraulic, solid, over head cam. Don't equate hydraulic lifter "pump up" and "valve float" as being one and the same; though similar, there are slight differences. Valve float is basically the inability of the springs to control valve action; inertia loads/velocity of lifter, push rod, rocker, valve and retainer over whelm the spring and the lifter/cam follower are no longer in contact with the cam lobe. How far the valves are open is dependent on how far are the lifters/cam follower is off the cam lobe. Hydraulic lifter "pump up" is thought to be when piddle valve inside the lifter body can not bleed off excess oil, thus the preload space is taken up with oil; this too will hold valves open.

Do both intake and exhaust valves float at the same time or do the heavier intake valves always float first? Where ever the weak springs are.

When does this condition cause contact between the piston dome and valve face? Thank you.
When the pistons and the valves try to occupy the same space at the same time
 
When the valves float, or the lifters pump up as they launch over the closing ramp, it is generally the exhaust valve that hits, as the piston is coming up towards the exhaust valve when it is being held open, and the piston is going down away from the intake valve if it were floating. Yeah, I think I remember that right. Haven't thought about it for awhile.
 
^^ what he says and him too! Piston chases the exhaust valve shut OR maybe it catches up to it!
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Stolen chevy right on the carpet in 1st gear,buddy recovered his truck (engine was still hot,guy was bleeding on the ground) and i had the (dis) pleasure of tearing it down. Found pieces of piston in the air cleaner. Yup it was toast. When we overhauled it months before,never considered floating valves at the time....
 
valve float or lack of compression ? what is compression of motor ?
 
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