Lilfter Preload vs. Pump Up
I would say just rpm as far as pump up is concerned with regards to the two items you've asked above. If you are talking about the lifter compressing then maybe pre-load would be something to look at as well as not enough may allow for compression to occur druing the lifting of the valves. Also, something else to consider would be if not enough spring pressure is used the lifter may pump up as well I would think as not enough pressure will be there to hold the pushrod against the cup as the lifter travels over the centerlines of the lobes and back down the lobe. I'm sure the experts will chime in here in a second though. Should make for an interesting thread.
Maybe I can clairify, if I understand your question correctly.
Lifter pump up is a process that occurs with every start-up to some degree. Every time the engine is stopped, the valve springs on the valves being lifted by the cam lobes are pressing against the oil pump plunger/piston built into each hydraulic lifter. In time, this squeezes the oil out of the oil chamber in the lifter and there is slack in the valvetrain. On the next start and warm-up cycle, the the lifters pump-up (fill the oil chambers with oil) this is due to the oil pressure rise from the main oil pump and the plunging/pumping cycles within the lifters themselves due to actuation by the cam.
Pre load is akin to setting the valve clearances on mechanical lifters. Net or zero lash ocurs hen the heel of the cam is against the lifter (no lift applied) and there is no slack in the valve train (rocker arm to valve, rocker arm to push rod, pushrod to lifter, and lifter to cam lobe. Also, the piston/plunger within the lifter should not be compressed, thus squishing the oil out of the oil chamber. Once zero lash is determined, if you have adjustable lifters, you can now set the pre load with the adjusting nut ant lock it down. Alternately, if you have non-adjustable lifters, you can adjust the pre load by a combination of selecting the correct push rod length and shimming the rocker arm base if necessary.
I hope that this helps.
Steve
Lifter pump up is a process that occurs with every start-up to some degree. Every time the engine is stopped, the valve springs on the valves being lifted by the cam lobes are pressing against the oil pump plunger/piston built into each hydraulic lifter. In time, this squeezes the oil out of the oil chamber in the lifter and there is slack in the valvetrain. On the next start and warm-up cycle, the the lifters pump-up (fill the oil chambers with oil) this is due to the oil pressure rise from the main oil pump and the plunging/pumping cycles within the lifters themselves due to actuation by the cam.
Pre load is akin to setting the valve clearances on mechanical lifters. Net or zero lash ocurs hen the heel of the cam is against the lifter (no lift applied) and there is no slack in the valve train (rocker arm to valve, rocker arm to push rod, pushrod to lifter, and lifter to cam lobe. Also, the piston/plunger within the lifter should not be compressed, thus squishing the oil out of the oil chamber. Once zero lash is determined, if you have adjustable lifters, you can now set the pre load with the adjusting nut ant lock it down. Alternately, if you have non-adjustable lifters, you can adjust the pre load by a combination of selecting the correct push rod length and shimming the rocker arm base if necessary.
I hope that this helps.
Steve
I was under the impression that pump up, atleast atleast in the context of the question that is being asked, is the plunger in the lifter actually moving up relative to the body of the lifter during the time the lifter stops lifting (once it has reached the centerline of the cam lobe) and starts going down the down side of the cam lobe.
Last edited by DAPSUPRSLO; Jan 9, 2006 at 10:27 AM.
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From: Little Rhody
I have been reading in several threads that too much preload results in pump up and holding the valves open. Some have found too much preload on the Morel lifters have done this, and some with stock. I thought pump up was the result of the onset of valve float, not vice versa. Everything I have read in technical articles states that pump up results from slop in the valve train usually when the springs can't keep up and the lifter tries to take out the slack. But many threads on this forum are indicating that lifter preload can cause pump up to occur.
Originally Posted by vettenuts
I have been reading in several threads that too much preload results in pump up and holding the valves open. Some have found too much preload on the Morel lifters have done this, and some with stock. I thought pump up was the result of the onset of valve float, not vice versa. Everything I have read in technical articles states that pump up results from slop in the valve train usually when the springs can't keep up and the lifter tries to take out the slack. But many threads on this forum are indicating that lifter preload can cause pump up to occur.
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From: Little Rhody
I think this is the root of my question, is pump up the cause or the effect. Recent information about altering (lowering) preload providing better RPM capability makes me wonder.
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Originally Posted by vettenuts
I think this is the root of my question, is pump up the cause or the effect. Recent information about altering (lowering) preload providing better RPM capability makes me wonder.
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Verdad Gallardo In my opinion, the main danger of too much pre-load is that the valves can unseat when on the heel of the cam, cutting compression, reducing power and burning valves. Too little pre-load and the valve train is noisy, wear is increased and you don't get full valve lift.
Steve
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From: K-W, Ontario
Originally Posted by Steve Bryant
Too little pre-load ... wear is increased and you don't get full valve lift.
I'm not sure I understand the reason for not allowing full valve lift, or increasing
wear?
Originally Posted by Adrenaline_Z
I'm not sure I understand the reason for not allowing full valve lift, or increasing
wear?
wear?
That's right, too little or no pre-load and you get a fair amount of movement of the piston within the lifter, thus reducing valve lift. This is not desirable, it's just what happens.
Steve
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From: Little Rhody
That would also be tough on the clip holding in the piston.
I have been reading David Vizards book and he states that pump up is usually the result of slack in the valve train (onset of float) rather then the lifter causing float. But I also thought that valving could cause the lifter to pump up as well holding the valve open and the resulting loss of power.
I have been reading David Vizards book and he states that pump up is usually the result of slack in the valve train (onset of float) rather then the lifter causing float. But I also thought that valving could cause the lifter to pump up as well holding the valve open and the resulting loss of power.
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Originally Posted by Steve Bryant
That's right, too little or no pre-load and you get a fair amount of movement of the piston within the lifter, thus reducing valve lift. This is not desirable, it's just what happens.
of Pre-load is to self adjust and take up slack as the valve train parts wear down.
Once you have correctly figured pushrod length, rocker tip alignment, etc., the
pre-load can be set to maintain a certain amount of correction as parts wear down.
The seat is always slopping around to some degree causing a variance in lift
at the valve. For this reason, I believe high output race motors will use a solid cam.
For peformance setups, modest amounts of pre-load can be set to limit the
travel of the plunger...which is getting closer to the function of a solid lifter.
This is one of the tricks I was shown to get a little more power.
As far as I'm aware, the lifter will pump up if the valve floats and creates clearance
between the cam lobe and valve tip.
The intial pre-load amount will always return.
.
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I think all the right info is here, just scattered a bit. Here's my version:
o 'Preload' per the factories is the setting/adjusting of the hydraulic piston in the lifter somewhere near it's mid-travel point, so that it can extend to account for heat expansion or contract to compensate for wear.
o 'Pump up' as the word is normally used by performance enthusiasts, is the lifter doing it's thing and taking up what it sees as 'clearance' but which is actually valve float. Thus, when the cam rotates to the base circle, the valve is still propped open, leaking compression, until the lifter adjusts itself back to normal.
o By setting the preload very small, the lifter seat cannot move far enough to prop the valve open very much, so the power loss at and immediately after valve float is reduced. Clearly this is a band aid. If it's happening regularly, you need better valve gear or less RPM!
o Vizard actually makes another point I hadn't though of, namely that even at the best of times, oil contains a fair bit of very compressible air which, especially with stout springs and high lift, means that as much as 0.020" 'collapse' can occur during a valve event, robbing lift and duration from the nominal cam profile. His solution is to select longer push rods and adjust the lifters within a few thous of bottoming out completely when cold, thus limiting the potential collapse. He says this rarely fails to give a 20 HP gain.
o He also says that in his testing, Royal Purple oil seems less prone to air entrainment and so reduces collapse and adds power in hydraulic cam applications.
o 'Preload' per the factories is the setting/adjusting of the hydraulic piston in the lifter somewhere near it's mid-travel point, so that it can extend to account for heat expansion or contract to compensate for wear.
o 'Pump up' as the word is normally used by performance enthusiasts, is the lifter doing it's thing and taking up what it sees as 'clearance' but which is actually valve float. Thus, when the cam rotates to the base circle, the valve is still propped open, leaking compression, until the lifter adjusts itself back to normal.
o By setting the preload very small, the lifter seat cannot move far enough to prop the valve open very much, so the power loss at and immediately after valve float is reduced. Clearly this is a band aid. If it's happening regularly, you need better valve gear or less RPM!
o Vizard actually makes another point I hadn't though of, namely that even at the best of times, oil contains a fair bit of very compressible air which, especially with stout springs and high lift, means that as much as 0.020" 'collapse' can occur during a valve event, robbing lift and duration from the nominal cam profile. His solution is to select longer push rods and adjust the lifters within a few thous of bottoming out completely when cold, thus limiting the potential collapse. He says this rarely fails to give a 20 HP gain.
o He also says that in his testing, Royal Purple oil seems less prone to air entrainment and so reduces collapse and adds power in hydraulic cam applications.
lifter pump up Lifter pump up is a function of llifter pre load, valve float, and oil pressure. You are pretty limited on valve spring pressure so valve float is pretty much a given if you push the rpm too high.
In a hydraulic lifter racing engine you adjust the valves for zero preload on a hot engine. That way the lifters can not pump up during valve float and hold the valves open. You need lifters with strong tru arc clips holding the push rod cup and piston in place. Most stock type lifters have cheap bent wire clips.
Street engines can be adjusted with about .010" to .015" preload hot. You obviously need adjustable rocker arms to do this.
As Bill stated, if the oil is aerated the lifters will collapse a bit reducing both lift and duration. Increasing the oil pressure will help. The best solution is dry sumping the engine if you indeed want or need to keep a true hydraulic lifter in the engine.
Stock eliminator racers have another trick. They prop up the push rod cup -piston with a steel pin inside the hydraulic lifter. The pin keeps the lifter from fully collapsing if the oil does get aerated - almost a certainty. Some cam companies sell these lifters but don't advertise them.
By the way, I've built hundreds of hydraulic lifter racing engines through the years.
Steve
In a hydraulic lifter racing engine you adjust the valves for zero preload on a hot engine. That way the lifters can not pump up during valve float and hold the valves open. You need lifters with strong tru arc clips holding the push rod cup and piston in place. Most stock type lifters have cheap bent wire clips.
Street engines can be adjusted with about .010" to .015" preload hot. You obviously need adjustable rocker arms to do this.
As Bill stated, if the oil is aerated the lifters will collapse a bit reducing both lift and duration. Increasing the oil pressure will help. The best solution is dry sumping the engine if you indeed want or need to keep a true hydraulic lifter in the engine.
Stock eliminator racers have another trick. They prop up the push rod cup -piston with a steel pin inside the hydraulic lifter. The pin keeps the lifter from fully collapsing if the oil does get aerated - almost a certainty. Some cam companies sell these lifters but don't advertise them.
By the way, I've built hundreds of hydraulic lifter racing engines through the years.
Steve
Originally Posted by MadBill
I think all the right info is here, just scattered a bit. Here's my version:
o 'Preload' per the factories is the setting/adjusting of the hydraulic piston in the lifter somewhere near it's mid-travel point, so that it can extend to account for heat expansion or contract to compensate for wear.
o 'Pump up' as the word is normally used by performance enthusiasts, is the lifter doing it's thing and taking up what it sees as 'clearance' but which is actually valve float. Thus, when the cam rotates to the base circle, the valve is still propped open, leaking compression, until the lifter adjusts itself back to normal.
o By setting the preload very small, the lifter seat cannot move far enough to prop the valve open very much, so the power loss at and immediately after valve float is reduced. Clearly this is a band aid. If it's happening regularly, you need better valve gear or less RPM!
o Vizard actually makes another point I hadn't though of, namely that even at the best of times, oil contains a fair bit of very compressible air which, especially with stout springs and high lift, means that as much as 0.020" 'collapse' can occur during a valve event, robbing lift and duration from the nominal cam profile. His solution is to select longer push rods and adjust the lifters within a few thous of bottoming out completely when cold, thus limiting the potential collapse. He says this rarely fails to give a 20 HP gain.
o He also says that in his testing, Royal Purple oil seems less prone to air entrainment and so reduces collapse and adds power in hydraulic cam applications.
o 'Preload' per the factories is the setting/adjusting of the hydraulic piston in the lifter somewhere near it's mid-travel point, so that it can extend to account for heat expansion or contract to compensate for wear.
o 'Pump up' as the word is normally used by performance enthusiasts, is the lifter doing it's thing and taking up what it sees as 'clearance' but which is actually valve float. Thus, when the cam rotates to the base circle, the valve is still propped open, leaking compression, until the lifter adjusts itself back to normal.
o By setting the preload very small, the lifter seat cannot move far enough to prop the valve open very much, so the power loss at and immediately after valve float is reduced. Clearly this is a band aid. If it's happening regularly, you need better valve gear or less RPM!
o Vizard actually makes another point I hadn't though of, namely that even at the best of times, oil contains a fair bit of very compressible air which, especially with stout springs and high lift, means that as much as 0.020" 'collapse' can occur during a valve event, robbing lift and duration from the nominal cam profile. His solution is to select longer push rods and adjust the lifters within a few thous of bottoming out completely when cold, thus limiting the potential collapse. He says this rarely fails to give a 20 HP gain.
o He also says that in his testing, Royal Purple oil seems less prone to air entrainment and so reduces collapse and adds power in hydraulic cam applications.
__________________
Steve Demirjian
Race Engine Development
Oceanside, Ca.
760-630-0450
web: www.raceenginedevelopment.com/
e-mail: race-engine-development@***.net
Steve Demirjian
Race Engine Development
Oceanside, Ca.
760-630-0450
web: www.raceenginedevelopment.com/
e-mail: race-engine-development@***.net
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Good call on the pre-load setting. I'll set mine cold initially, then run
the motor to temp.
Using my dial indicator, I'll re-set the pre-load to 0.005" and then run the
motor. I have been able to get 3HP on the dyno by resetting the valves.
My idle vacuum picks up a few points as well which means it's not only a
high RPM application.
I still don't know of any hydraulic cams in Pro-stock, or similar race classes.
That is what I meant by 'high output race motor'. Sorry, I should have been
more specific.
the motor to temp.
Using my dial indicator, I'll re-set the pre-load to 0.005" and then run the
motor. I have been able to get 3HP on the dyno by resetting the valves.
My idle vacuum picks up a few points as well which means it's not only a
high RPM application.
I still don't know of any hydraulic cams in Pro-stock, or similar race classes.
That is what I meant by 'high output race motor'. Sorry, I should have been
more specific.
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So, is the aeration problem (which I first heard about on this thread) a reason that 1) LS1's seem to run such high oil pressure, and 2) GM dry sumped the LS7?
Overall, this just raises the question, especially with adjustable rockers needed anyway, that more LS1 engines aren't using solid lifters. Is it rule restriction in the racing classes?
Overall, this just raises the question, especially with adjustable rockers needed anyway, that more LS1 engines aren't using solid lifters. Is it rule restriction in the racing classes?
Yes, the ls1 has been said to have a pretty poor oiling system from the standpoint of introducing a lot of air into the oil during high rpm operation. I believe alot of it comes from the undersized pick up of the oil pump and the way the oil just sloshes all over the crank shaft. I think this needs to discussed as a new thread. Anyone else???