What happens when you float a lifter?

[willys1]

I was revving my motor very high a few weeks ago in nuetral,(close to 6000rpm) after that it was ticking for awhile.Now when I rev it really high like that it sounds like a lifter or Rocker arm is hammering.What actually happens when you float a valve/lifter?

 

[5ohturbostang]

I was revving my motor very high a few weeks ago in nuetral,(close to 6000rpm)

 

[Realmongo]

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

 

[willys1]

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

WOW,,,guess I didnt float a lifter

 

[willys1]

I know,I know,,,but I was trying to get someones attention!!

 

[8950HO]

I was revving my motor very high a few weeks ago in nuetral,(close to 6000rpm) after that it was ticking for awhile.Now when I rev it really high like that it sounds like a lifter or Rocker arm is hammering.What actually happens when you float a valve/lifter?

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

 

[willys1]

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

I didnt realise I was going that high till I look at the tach.

 

[8950HO]

If there`s a hammering noise now,there could be mechanical damage,eg,a bent pushrod as one example.

This happened to me years ago in a 72 Mach 1,351C.I let her rip in gear,(not in neutral) one time and the next thing I heard was a serious ticking/hammering sound from the valve train...sure enough,after pulling the valve cover and taking a look,one of the pushrods was bent big time.

Just a thought.

 

[Roland69]

what is the rev limiter set at from factory or is there one.

 

[5ohturbostang]

I know,I know,,,but I was trying to get someones attention!!

thats how i blew up my chebby,revvin showin off at my uncles next thing ya know knock knock but nobody was at the door lol.all i gots to say is did ya learn anything?:SNSign:

 

[Michael Yount]

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, or to keep the valve in contact with the seat. Imagine lifter/lobe interface as the lobe is rotating past peak lift. If the spring weren't strong enough 1) as the lobe moves past it's peak, the lifter roller actually loses contact with lobe and/or 2) 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. The valves bouncing off their seats upon closing usually occurs before the lifter parts company with the lobe.

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?

Roland - the factory ecu has a 6250 rev limiter.

 

[willys1]

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?

Mike I was just trying to get someones attention,,thats it..I have a catted X pipe now,its got a meaner growl now,but is quieter,if that makes sense..

 

[bertman]

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:

 

[willys1]

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:

Well from hearing what a "floated" lifter actually is I dont think I have one because its "not" constant..Yeah "04Sleeper" (Kevin) talked me into getting a shift lite. Im not sure who's better yet,him or Hissin50 or M.Yount!! LOL,,,,
Thanks for the advice and explanation

 

[Michael Yount]

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 of pistons hitting valves because the valves 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.

 

[willys1]

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.

Vavle float,gotcha
I had a 350 chebby once that actually spit out a main bearing causing the piston to travel all the way up and slap the head each time it went up!! Talk about a engine "knock"!!

 

[Michael Yount]

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

 

[willys1]

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

It was 20 years ago,but I do remember driving it for a few weeks like that..I sold it to my boss (1976 FireBird with SBC) he ripped it apart and showed me.The piston was shiny and matted down on top.

 

[Euphoric306]

umm... how would a main bearing cause the piston to travel all the way up to the head?

maybe his rod cap came off?

 

[04sleeper]

Billy,

You can get a broom stick and put one end of it up to the valve cover and the other end to your ear and hear where it might be coming from.

Move it all along the valve covers until you hear the tick, (or noise), get louder.

This should give you an idea where to begin.

Parts stores sell tools that do this but it has worked for me in the past.

Either way it sounds like you are going to have to pull off the valve covers and do some checking.