What could cause the vavle stem tip to get 'beat up'?
11-09-2009, 08:22 PM
#16
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Join Date: May 2004
Location: Bay Area, CA
Posts: 2,001
Caprice, this is the real definition of valve float courtesy of about.com, "Definition: A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valve train components. The onset of valve float prevents higher-rpm operation. Extended periods of valve float will damage the valve train."
The valve never looses contact with the rocker.
see it for yourself:
http://www.youtube.com/watch?v=_REQ1PUM0rY
the valve tip just wiggles around, no bouncing or slamming of the rocker.
The valve never looses contact with the rocker.
see it for yourself:
http://www.youtube.com/watch?v=_REQ1PUM0rY
the valve tip just wiggles around, no bouncing or slamming of the rocker.
There is valve float and there is valve bounce - the later is when the spring cannot control the valve dropping onto the seat due to the intensity of the closing ramp - this will cause the valve to bounce on/off the seat several times, it will hit the rocker and cause damage there over time.
Incorrect spring pressure
Poor quality valves
incorrect alignment/geometry of rocker arms causing scrubbing rather than rolling.
there's quite a few possibilities, would have to see the parts in person.
Last edited by MachinistOne; 11-09-2009 at 08:26 PM.
11-09-2009, 10:56 PM
#17
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Join Date: Jul 2009
Posts: 75
All the parts move around - they don't magically stick together.
There is valve float and there is valve bounce - the later is when the spring cannot control the valve dropping onto the seat due to the intensity of the closing ramp - this will cause the valve to bounce on/off the seat several times, it will hit the rocker and cause damage there over time.
Incorrect spring pressure
Poor quality valves
incorrect alignment/geometry of rocker arms causing scrubbing rather than rolling.
there's quite a few possibilities, would have to see the parts in person.
There is valve float and there is valve bounce - the later is when the spring cannot control the valve dropping onto the seat due to the intensity of the closing ramp - this will cause the valve to bounce on/off the seat several times, it will hit the rocker and cause damage there over time.
Incorrect spring pressure
Poor quality valves
incorrect alignment/geometry of rocker arms causing scrubbing rather than rolling.
there's quite a few possibilities, would have to see the parts in person.
11-09-2009, 11:36 PM
#18
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Join Date: May 2004
Location: Bay Area, CA
Posts: 2,001
Simply put, you are incorrect.
The weight of the lifter is not as much a concern as is the weight of components on the "fast" side of the valve train - valve, spring, retainer, etc. Much of valve float is cause by push rod flex, the rod flexes on the opening ramp of the cam, when it straightens out it basically throws the valve or floats it. The effect on power is less with float than with bounce, but both cause damage over time to all the components in the system.
Rev kits are there to keep contact between the lifter and the cam in solid roller applications to reduce bounce of the lifter and subsequent damage to the lobes and rollers. They are NOT designed to be a substitute for proper spring pressure, if adding a rev kit picks up significant RPM and power then your valve train was improperly designed from the start.
The weight of the lifter is not as much a concern as is the weight of components on the "fast" side of the valve train - valve, spring, retainer, etc. Much of valve float is cause by push rod flex, the rod flexes on the opening ramp of the cam, when it straightens out it basically throws the valve or floats it. The effect on power is less with float than with bounce, but both cause damage over time to all the components in the system.
Rev kits are there to keep contact between the lifter and the cam in solid roller applications to reduce bounce of the lifter and subsequent damage to the lobes and rollers. They are NOT designed to be a substitute for proper spring pressure, if adding a rev kit picks up significant RPM and power then your valve train was improperly designed from the start.
11-10-2009, 08:55 PM
#20
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Join Date: Jul 2009
Posts: 75
I stand by what I say. and to quote Circle Track Magazine,
"Valve float occurs when the valvesprings are incapable of holding the valvetrain against the camshaft lobe after peak lift. This happens when either the weight of the combined valvetrain components or the rpm speed of the engine creates so much inertia that the spring is no longer able to control the valve. The most common response to valve float is to increase the strength of the spring so that it can better control valve motion. But stronger springs generally weigh more and cause their own problems. Achieving the optimum strength-to-weight ratio is a delicate balancing act for every engine builder."
check out the article :http://www.circletrack.com/techartic...oat/index.html
Oh, and you basically just reitterated what i said about a rev kit.
"a rev kit puts additional spring pressure on the lifter to keep it in its bore and following the camshaft lobe."
"Rev kits are there to keep contact between the lifter and the cam in solid roller applications to reduce bounce of the lifter and subsequent damage to the lobes and rollers."
Rev kits allow you an additional margin of engine range, no matter how insignificant it may be.
"Valve float occurs when the valvesprings are incapable of holding the valvetrain against the camshaft lobe after peak lift. This happens when either the weight of the combined valvetrain components or the rpm speed of the engine creates so much inertia that the spring is no longer able to control the valve. The most common response to valve float is to increase the strength of the spring so that it can better control valve motion. But stronger springs generally weigh more and cause their own problems. Achieving the optimum strength-to-weight ratio is a delicate balancing act for every engine builder."
check out the article :http://www.circletrack.com/techartic...oat/index.html
Oh, and you basically just reitterated what i said about a rev kit.
"a rev kit puts additional spring pressure on the lifter to keep it in its bore and following the camshaft lobe."
"Rev kits are there to keep contact between the lifter and the cam in solid roller applications to reduce bounce of the lifter and subsequent damage to the lobes and rollers."
Rev kits allow you an additional margin of engine range, no matter how insignificant it may be.
Last edited by cusz28; 11-10-2009 at 09:01 PM.
11-11-2009, 08:40 PM
#23
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Join Date: Jul 2009
Posts: 75
looks like someone's getting an attitude. You see, My problem isn't "restating whatever crap I've read", it's being taught right from the start and having the ability to back up everything i've been saying. you haven't. you have no grounds to dispute the fact that i can PROOVE YOU WRONG. I, personally, don't have any problem with being wrong. Actually, you are the one that has re-stated facts, my very own, in fact. stop being blind and proove me wrong, please... stop arguing with me and show me proof. i would love to see it. now, can we PLEASE move on with our OP?
11-11-2009, 09:50 PM
#25
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Join Date: May 2004
Location: Bay Area, CA
Posts: 2,001
Wow...
You didn't even read through the whole article that you quoted, it backs up what I have already stated and goes against what you have claimed.
After pointing this out I am done, my credentials are known and almost all of my knowledge concerning motors is from first hand experience not from "about.com" as you quoted earlier
From: http://www.circletrack.com/techartic...oat/index.html
I have highlighted the most relevant sections.
My points had been...
"fast side of the valve train where mass has the most effect leads to valve float"
"All the parts move around causing damage"
Without connecting all the dots, I will say that there is discussion about reducing valve train weight on the fast side of the system such as springs and retainers, we add stiffer and hence heavier push rods to improve the system and it's effect on valve float is almost nil because it's on the "slow side" of the system.
You said
and the article you quote specifically points out the error of your claims...
Try researching "lifter loft" - that's more like what you are describing, and Comp has a line of cams with the sole intent of lofting the lifter off the cam lobe to make more lift in a lift limited racing class.
You came in guns blazing at me in the other thread claiming that higher ratio rockers change cam duration and were proven wrong on a very very simple concept dealing with engines, once again you have done it in this thread and had the stupidity to quote an article which directly contradicts what you claim...
Anyone else reading this thread can connect the dots
You didn't even read through the whole article that you quoted, it backs up what I have already stated and goes against what you have claimed.
After pointing this out I am done, my credentials are known and almost all of my knowledge concerning motors is from first hand experience not from "about.com" as you quoted earlier
From: http://www.circletrack.com/techartic...oat/index.html
I have highlighted the most relevant sections.
Valvetrain Repair - Fixing Valve Float
Diagnosing Valve Float Issues Found In A Postseason Engine Rebuild
By Jeff Huneycutt
Photography by Jeff Huneycutt
While making our usual rounds of race shops, we came across a problem that plagues many racers and unnecessarily costs them lots of money-and we thought we'd share the solution with you. While performing a rebuild of a Late Model-style Chevy race engine, cylinder head specialist Kevin Troutman of KT Engine Development saw the telltale signs of classic valve float. The racer either didn't notice or just didn't bother to mention the problem to KT Engines, and the results were costly. But the good news is that valve float can be avoided.
Valve float occurs when the valvesprings are incapable of holding the valvetrain against the camshaft lobe after peak lift. This happens when either the weight of the combined valvetrain components or the rpm speed of the engine creates so much inertia that the spring is no longer able to control the valve. The most common response to valve float is to increase the strength of the spring so that it can better control valve motion. But stronger springs generally weigh more and cause their own problems. Achieving the optimum strength-to-weight ratio is a delicate balancing act for every engine builder.
The most efficient and dependable race engines are able to hit the sweet spot in the triangle created between strength of the valvespring, weight of the valvetrain components (lifters, pushrods, rocker arms, valves, retainers, locks, and springs), and the engine's peak rpm levels. In order to maintain good valve control at higher rpm levels, many engine builders have begun reducing valvetrain weight (and therefore the overall valvetrain mass) by using beehive-shaped springs.
Comp Cams is leading the development of high-performance beehive springs, and the results have been good so far. The beehive-shaped spring has several advantages when used correctly. First, its conical shape makes it smaller at the top. This reduces mass in the area of the springs that moves the most every time the valve is opened. Second, the smaller size means that a smaller retainer is also used, reducing mass there as well. Third, the beehive spring is a single-spring design by necessity, and while it cannot be made with as much spring pressure as a more conventional, double-nested design, the simpler design makes it much lighter. Beehive springs are also used in GM's LS1 and LS2 engine designs, making it legal where rule books require "stock-type components only."
The lighter overall weight means that a smart engine builder has more options available for his build, such as using less spring pressure to get the same results. He can also maintain spring pressure to increase engine rpm before valve float occurs. Or he can experiment with even more radical camshaft designs that weren't possible with conventional springs. The one thing that must be remembered, however, is that while beehive springs can help offset the effects of valve float, it is still possible to float a valve when the right conditions are reached.
The Clues During teardown, Troutman says he first noticed the signs of valve float as soon as the rocker arms were pulled to reveal the tips of the valve stems. Because the intake valve is larger than the exhaust valve, and therefore heavier, it almost always enters a float condition first. Whenever the valve floats, the "floor" of the system, or the closing ramp of the cam lobe, falls out from underneath the system. This creates gaps along the line of components between the cam and the valve stem. When the spring is finally able to overcome the inertia of the moving valve and begin closing it, its movement of the valve is uncontrolled. This movement can be very harsh as the spring slams the valve closed. Because of this, one area of high wear is the valve tip, which is repeatedly smashed into the pad or roller tip of the rocker arm.
A damaged valve tip will most often appear as though part of the metal has flaked off. When you have this condition, it is sometimes possible to grind a few thousandths of material off the end of the valve stem, but this is rarely worth it. Grinding down the end of the valve stem, even if only a few thousandths of an inch, changes the valvetrain angles, which can lead to other problems. Also, even if you grind off the portion that is visibly damaged, there is no easy way to tell if the remainder of the valve hasn't been compromised. It's far better to throw the valve away and install a replacement.
The action of the valve being slammed closed is also quite hard on the seats-both at the valve and the combustion chamber. In the worst-case scenario, the valve is smashed against the seat of the combustion chamber so hard that the valve "tulips" or becomes warped. It's easy to tell when this happens, even if you cannot see it, because the valve won't hold a seal against the seat. In less extreme cases, the seat cut into the valve will be pounded until it becomes concave. This was the situation found on our engine. The seat in the combustion chamber may show signs of damage by being wider than originally cut. On a typical three-angle valve job, the 45-degree cut where the valve actually seats against the chamber is usually only 0.040 inch wide. The intake seats in the combustion chamber on this engine were nearly 0.100 inch wide. Particular care will also be required when inspecting the lifters and camshaft after the short-block is torn down.
Diagnosing Valve Float Issues Found In A Postseason Engine Rebuild
By Jeff Huneycutt
Photography by Jeff Huneycutt
While making our usual rounds of race shops, we came across a problem that plagues many racers and unnecessarily costs them lots of money-and we thought we'd share the solution with you. While performing a rebuild of a Late Model-style Chevy race engine, cylinder head specialist Kevin Troutman of KT Engine Development saw the telltale signs of classic valve float. The racer either didn't notice or just didn't bother to mention the problem to KT Engines, and the results were costly. But the good news is that valve float can be avoided.
Valve float occurs when the valvesprings are incapable of holding the valvetrain against the camshaft lobe after peak lift. This happens when either the weight of the combined valvetrain components or the rpm speed of the engine creates so much inertia that the spring is no longer able to control the valve. The most common response to valve float is to increase the strength of the spring so that it can better control valve motion. But stronger springs generally weigh more and cause their own problems. Achieving the optimum strength-to-weight ratio is a delicate balancing act for every engine builder.
The most efficient and dependable race engines are able to hit the sweet spot in the triangle created between strength of the valvespring, weight of the valvetrain components (lifters, pushrods, rocker arms, valves, retainers, locks, and springs), and the engine's peak rpm levels. In order to maintain good valve control at higher rpm levels, many engine builders have begun reducing valvetrain weight (and therefore the overall valvetrain mass) by using beehive-shaped springs.
Comp Cams is leading the development of high-performance beehive springs, and the results have been good so far. The beehive-shaped spring has several advantages when used correctly. First, its conical shape makes it smaller at the top. This reduces mass in the area of the springs that moves the most every time the valve is opened. Second, the smaller size means that a smaller retainer is also used, reducing mass there as well. Third, the beehive spring is a single-spring design by necessity, and while it cannot be made with as much spring pressure as a more conventional, double-nested design, the simpler design makes it much lighter. Beehive springs are also used in GM's LS1 and LS2 engine designs, making it legal where rule books require "stock-type components only."
The lighter overall weight means that a smart engine builder has more options available for his build, such as using less spring pressure to get the same results. He can also maintain spring pressure to increase engine rpm before valve float occurs. Or he can experiment with even more radical camshaft designs that weren't possible with conventional springs. The one thing that must be remembered, however, is that while beehive springs can help offset the effects of valve float, it is still possible to float a valve when the right conditions are reached.
The Clues During teardown, Troutman says he first noticed the signs of valve float as soon as the rocker arms were pulled to reveal the tips of the valve stems. Because the intake valve is larger than the exhaust valve, and therefore heavier, it almost always enters a float condition first. Whenever the valve floats, the "floor" of the system, or the closing ramp of the cam lobe, falls out from underneath the system. This creates gaps along the line of components between the cam and the valve stem. When the spring is finally able to overcome the inertia of the moving valve and begin closing it, its movement of the valve is uncontrolled. This movement can be very harsh as the spring slams the valve closed. Because of this, one area of high wear is the valve tip, which is repeatedly smashed into the pad or roller tip of the rocker arm.
A damaged valve tip will most often appear as though part of the metal has flaked off. When you have this condition, it is sometimes possible to grind a few thousandths of material off the end of the valve stem, but this is rarely worth it. Grinding down the end of the valve stem, even if only a few thousandths of an inch, changes the valvetrain angles, which can lead to other problems. Also, even if you grind off the portion that is visibly damaged, there is no easy way to tell if the remainder of the valve hasn't been compromised. It's far better to throw the valve away and install a replacement.
The action of the valve being slammed closed is also quite hard on the seats-both at the valve and the combustion chamber. In the worst-case scenario, the valve is smashed against the seat of the combustion chamber so hard that the valve "tulips" or becomes warped. It's easy to tell when this happens, even if you cannot see it, because the valve won't hold a seal against the seat. In less extreme cases, the seat cut into the valve will be pounded until it becomes concave. This was the situation found on our engine. The seat in the combustion chamber may show signs of damage by being wider than originally cut. On a typical three-angle valve job, the 45-degree cut where the valve actually seats against the chamber is usually only 0.040 inch wide. The intake seats in the combustion chamber on this engine were nearly 0.100 inch wide. Particular care will also be required when inspecting the lifters and camshaft after the short-block is torn down.
My points had been...
"fast side of the valve train where mass has the most effect leads to valve float"
"All the parts move around causing damage"
Without connecting all the dots, I will say that there is discussion about reducing valve train weight on the fast side of the system such as springs and retainers, we add stiffer and hence heavier push rods to improve the system and it's effect on valve float is almost nil because it's on the "slow side" of the system.
You said
sorry, machinist, during valve float, the rocker stays in contact with the valve.
Try researching "lifter loft" - that's more like what you are describing, and Comp has a line of cams with the sole intent of lofting the lifter off the cam lobe to make more lift in a lift limited racing class.
You came in guns blazing at me in the other thread claiming that higher ratio rockers change cam duration and were proven wrong on a very very simple concept dealing with engines, once again you have done it in this thread and had the stupidity to quote an article which directly contradicts what you claim...
Anyone else reading this thread can connect the dots
Last edited by MachinistOne; 11-11-2009 at 09:53 PM.
11-14-2009, 08:20 AM
#27
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Join Date: Jun 2006
Location: upstate New York
Posts: 439
I agree that valve float could cause the problems the OP has, but another culprit *might* be excess valve lash- In both cases there are moments when there is gaps in the valve train components, and when that gap is taken up by the lobes of the cam pushing the lifter and valve stem, there is a small collision, rather than a smooth push- that collision is a hammering action, rather than a smooth acceleration of the components, and repeated long enough and hard enough will cause fatigue and component failures-
If you have excess lash, you can usually hear the ticking or clicking as these pieces are banging together- not a happy sound-
If you have excess lash, you can usually hear the ticking or clicking as these pieces are banging together- not a happy sound-
11-14-2009, 10:33 AM
#28
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,678
looks like someone's getting an attitude. You see, My problem isn't "restating whatever crap I've read", it's being taught right from the start and having the ability to back up everything i've been saying. you haven't. you have no grounds to dispute the fact that i can PROOVE YOU WRONG. I, personally, don't have any problem with being wrong. Actually, you are the one that has re-stated facts, my very own, in fact. stop being blind and proove me wrong, please... stop arguing with me and show me proof. i would love to see it. now, can we PLEASE move on with our OP?
11-21-2009, 07:23 AM
#29
Registered User
Join Date: Feb 2004
Posts: 4,800
Let's just apply practical knowledge here. Forget we are talking valvetrain.
If you apply excessive pressure to a metal rod it bends right??
What happens if you take a hammer to the end? It mushrooms. Now what is it you are seeing?
If you apply excessive pressure to a metal rod it bends right??
What happens if you take a hammer to the end? It mushrooms. Now what is it you are seeing?
11-21-2009, 08:32 AM
#30
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Thread Starter
Join Date: Dec 1999
Location: Upstate New York,USA
Posts: 1,791
I'm still waiting for Jim to get back to me on what he meant by "beat up". I'll post as soon as he replies. *maybe* I can just drop by his shop later today.