What happens when you float a lifter?

Realmongo said:

Generally the lifter collapses, the valve goes shut and the engine shuts down.

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5ohturbostang said:

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8950HO said:

It`s common knowledge that you don`t rev an engine this high in neutral.
Why would you do this?

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Michael Yount said:

You 'float' valves; you 'collape' or 'pump up' lifters.

When you float a valve the valve spring isn't able to provide enough force to keep the lifter in contact with the cam lobe. Imagine lifter/lobe interface as the lobe is rotating past peak lift. If the spring weren't strong enough as the lobe moves past it's peak, the lifter roller actually loses contact with lobe and/or the valve will bounce on it's seat upon closing. This can also happen if the engine spins too fast to allow the springs to control the momentum of the valve train.

When the lifter loses contact with the lobe it creates clearances in the valve train and the oil pressure in the system tries to close those by 'pumping up' the lifter. If the lifter pumps up -- so it's plunger is all the way at the top of it's travel, once the lifter comes back in contact with the lobe, the result can be a hung open valve that won't seat completely - or that takes too long to seat. When that happens, cylinder pressure is reduced AND cylinder contents can be pumped back into the intake where if they're ignited can cause backfires through the intake system.

If the engine has springs that are too strong and the engine is revved too high, the spring pressure can overcome the hydraulic pressure in the lifter causing the lifter to 'collapse'. This creates unintended clearances in the valve train components as well.

Most of this simply goes away when the revs are reduced -- but if you've got ticking noises remaining after an over-rev, then dimensionally something has changed. Probably a good idea to pull the valve covers and see what you find. If there's nothing obvious, going back through and re-installing the rockers with the correct procedure may return quiet to the system.

Why were you revving it to 6000 in neutral?

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bertman said:

If you have a shift light When it comes on that means you dont go any higher. My wife did that to my car racing someone. She floated 2 lifters and bent one pushrod and broke one. Usually you bend or break a pushrod. Listen to the noise carefully to what side its coming from and pull the valve cover off and take a look. :SNSign:

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Michael Yount said:

Yeah - you'll want to get the terminology right before the flaming begins -- you don't 'float' lifters; you float valves.

And floating the valves by itself often causes no permanent damage. The most frequent symptom is simply a loss of power at higher revs, or missing/spitting/popping/backfiring in the intake. Continually doing it is bad for the springs and valvetrain and can cause things to break. What often happens with valve float, especially on the exhaust valve is that the valve hangs open a bit too long, and the piston smacks it on the way through TDC. That's what breaks valves, holes pistons, bends valve stems/pushrods, etc. It's not the valve float per se that does the damage -- but the result on pistons hitting valves that aren't where they're supposed to be because the spring couldn't control the valve movement properly. It's also possible during a missed shift/over-rev to 'fling' the lifter off the top of the lobe with enough force to cause spring bind -- that can break springs -- which often lets keepers/retainers go, valves drop into the cylinder, pistons smack them --- and much fun ensues.

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Michael Yount said:

"...each time it went up..." I kinda doubt it went up too many more times after stuff started hitting stuff.....

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