Yes Greg, pics of the differencials will be posted. The dif pics probably won't be posted until late September. The reason for this is they are somewhat special and we all know how fast certain parts are copied.

 

Chad,

Looking forward to seeing the pics of the valves and diffs in Sept. I know what you mean about people copying parts...

Greg A

 

Craig,

I should be posting pics of the intake valves and heads in a few days. No problem there. Just waiting for S Car Go Racing to send them to me.

As for the coping ............. hope there isn't an inside leak this time. The dif's should be safe as BC is a pretty safe person.

 

Here is a little blurp from Ferrea about their intake valve which we have incorporated into KA's motor.

Super Alloy Valves
Super Alloy... THE NEXT GENERATION OF VALVE TECHNOLOGY

Ferrea super alloy valves... represent the highest level of sophistication in valve technology. We proudly introduced the next generation of extreme heat resistant valves, specifically developed to withstand the brutal punishment of NHRA Top Fuel and Funny Car applications. We have developed a specially processed high nickel-based alloy, and a unique heat-treatment process, which yields extreme heat resistance and enormous tensile strength properties, (far beyond conventional Inconel materials).


These extraordinary valves will set the standards for all Supercharged, Turbocharged, Nitrous Oxide, Off-Shore Marine or 9.0 compressin restricted race motors. Many Top Fuel Dragster and Funny Car teams can confirm the performance and reliability of these new valves which are now available for many engine combinations including NASCAR, Sprint Car, Drag Race, and Off-Shore Marine applications.

We have expanded our offerings for the Top/Fuel and Funny/Car applications with a Super Alloy Valve available for every after-market head in both 11/32 & 3/8-stem sizes.

We are also reaching a fast growing segment in the Import Cars with the introduction of our New Super Alloy Import-Tuner Valve program. These valves are specially designed for use in racing engines that are subjected to extreme exhaust temperatures such as turbo, nitrous, or supercharged racing engines. No other valve on the market has been designed specifically for these applications. Once again Ferrea is setting the pace.

 

VALVE TRAIN
TROUBLESHOOTING GUIDE
Reprinted from our 2004 Automotive Catalog and Tech Guide
by Henry D. Manley III


STEADY STATE RPM ENGINE



Assembling a steady state rpm engine or a a narrow range oval track engine is perhaps the greatest challenge a builder can face today. This statement in no way denigrates the efforts of the drag race community. Success in the straight line arena depends on producing peak horsepower at a very high rpm level, with a large premium on the flatness of the power curve. No easy assignment! The added wrinkle in constructing an oval or marine engine, not of immediate concern in a drag race powerplant, is the existance of dangerous "fuss points" that will inject instability into the valve train. An unstable valve train drastically decreases the life of the components, inevitably leading to failure.


It is the responsibility of the builder to determine where the "fuss points" reside in the engine and be absolutely certain that none appear in the operating range of the engine. Determining the location of an engine's "fuss points" requires a Sprinton machine to detect where the springs drift into a harmonic state of discord that allows the valve train to become disunited and the valves to bounce on the seats.

Building an engine to run in a narrow rpm range for extended periods of time without knowing positively if that range contains any "fuss points" is strongly discouraged. But if access to a Sprinton is not possible, hopefully a few "bon mots" will benefit the engine builder.

1. The best marine engine builders change titanium valves after every race. Winston Cup valves only run one race. If the valves in your engine are experiencing bounce where the stresses are elevated to 40,000 psi from the normal 20,000 they may last 800,000 cycles or one five hundred mile race. But the fatigue life may be seriously compromised, and asking those valves to complete two or three more races may simply be beyond their fatigue life capabilities.

2. A valve spring cannot be judged solely on its ability to resist pressure loss. It is possible for a spring to control the valve train at 8400 rpm, end a race with minimal open load loss, yet be experiencing a "fuss point" at 8100 rpm that allows a serious valve bounce.

3. Moving an engine's rpm range up only 200 or 300 can have a major effect on the valve train. If a builder has researched ( or stumbled upon ) a combination that works in a certain range, boosting that range should not be undertaken without thoroughly revisiting the choice of valve springs and the weight of the reciprocating components.

CONCLUSIONS: In general, valve springs are NOT the place to affect economies. Purchase the best springs that have been proven to work with similar components both on Sprinton and in race engines. Lighten the valves and change them often, being sympathetic to the notion that they have a fatigue life that is seriously shortened by being bounced on the seats. Related components such as spring retainers and valve locks should be lightened, and pushrods should be stiff as well as light. Give us a call at Manley Performance; we are always happy to share our testing results to keep racers running at the end.

“You gotta be there at the end to win.�
Nothing could be more obvious; yet nothing could be more true.

At Manley Performance we have made an unlimited commitment to ensure that our customers will be there at the end when they use our products. The Manley commitment to product excellence is two phased.

First, we continue to research, test and introduce improved materials, designs, heat treatment and finishes that result in superior products.
Our HT titanium material, our impinged retainers, our Bead-Loc keepers and our swedged end pushrods are all examples of new and improved commodities for the racing fraternity

Second, we have extensively tested to determine exactly what is happening to the valve train in a running engine. Our goal is to fully comprehend the problems each product faces in order to build the best piece possible. Our valve operating temperature data, our unbelievably vast valve fatigue testing ( which we are convinced no other competitor has ever undertaken), and our comprehensive finite element analysis (FEA) of retainers are all illustrative of the depths to which we have probed to find real answers that result in real improvements.

There is another - absolutely crucial - ingredient in the success of a race engine, and that is the engine builder. The selection of related items such as camshafts and springs, and the preparation of the fuel system and the general state of the engine tune-up, all carry extremely heavy, often critical , responsibility for the success of the valve train components. It is for the concerned engine builder that these remarks are targeted, so that hopefully with our test results and experience we can point out problem areas in the valve train and offer suggestions to keep everyone running at the end.

Valves don’t just break. They are affected by temperatures and dynamic stress. Too much of either - or almost too much of both in combination - will result in valve failure. Valves MUST be kept within the temperature parameters of the material. Even the high temperature materials such as XH - 428 and XH - 430 stainless and HT titanium have finite limits. Items 6 and 7 expand on the subject of temperature.

First, let’s discuss dynamic stress. In a smooth running Winston Cup engine with no valve float the valves are experiencing 20,000 psi of stress. If valve float occurs, the stress can reach 50,000 psi and this will reduce the life expectancy of the part by over 90%. And this happens if the valve temperature does not increase, which is an unrealistic expectation. Elevated temperatures will quickly reduce the life of the valve even more. From these facts - derived from our exhaustive rotating beam fatigue test - it is obvious that CONTROLLING THE VALVE TRAIN can not be emphasized too strongly.

1. VALVE LOCK SCRUBBING
This is the first place to look for valve float. If the locks are leaving scuff marks on the valve stem above and below the keeper groove, the valve is bouncing on the seat and the valve gear (lock, retainer, spring) is separating. Nothing but trouble is on the horizon.



SUGGESTIONS: Lighten the valve train. If using stainless valves, move to titanium. If using titanium, move to thinner stems to reduce weight. Change to a lighter retainer. Buy better valve springs. Go to a stiffer (3/8� diameter) pushrod. Finally, work with your camshaft grinder to develop a profile that won’t toss the valve gear until eventual destruction.

2. MULTIPLE ROCKER PATTERN
The photo is fully illustrative of the multiple rocker contact areas on the valve tip. Since this type valve train is non-rotating by design, the only way the valve can rotate is if it experiences float. Again, disaster lurks around the corner when valve train instability is present.



SUGGESTION: See suggestions under #1.

3. RETAINER FIT
Retainer fit is an often over-looked issue. The steps on the retainer must match the I.D.’s of the spring package. Mismatch can cause the retainer to be overstressed and fail. Our FEA (finite element analysis ) highlights the most highly stressed areas of the retainer, and our discovery of these potential trouble spots is evident in the design of our pieces.



SUGGESTIONS: Use Manley titanium Super 7° ICD retainers with our exclusive impingement process that offers better abrasion resistance, improved impingement fatigue strength and an improved surface condition. Also, chamfer the I.D.’s of your spring to allow clearance between the spring and the corner radius of the retainer. If using springs with dampners, be certain to finish the ends of the dampners with a large radius and a smooth polish.

4. VALVE LOCK FIT
Do not underestimate the importance of proper fitting valve locks. The valve lock is designed to clamp on the stem of the valve - not in the root of the groove. The tongue of the lock is for locating purposes only. THERE ARE POORLY MACHINED LOCKS ON THE MARKET. Also, be certain the lock angle is compatible with the retainer angle. This is often not the case.



SUGGESTIONS: Use Manley Super 7° - either regular design or the safer Bead-Loc style - along with Manley Super 7° retainers. These are made in our own double spindle CNC lathes to exacting tolerances to assure proper fit.

5. VALVE SPRING "LIFT OFF"
Check the wear pattern in the photo. The coils are touching each other. Is this coil bind? No. The spring is actually lifting off the spring seat pad of the cylinder head causing the coils to touch each other. Springs have certain “fuss� points where in distinct rpm ranges they are in a harmonic state of discord and not under control. It is possible for a spring to control the valve train at 8500 rpm but be unable to do so at 8100 rpm.



SUGGESTIONS: Attempt to tune the “fuss point� out of the operating range of the engine with a different design valve spring. The best springs in the industry are Manley's. Also, stiffer pushrods and lighter valves and retainers will be beneficial.

 

6. SEAT INSERTS
Seat inserts are crucial to the successful control of valve temperature. Valves pass 75% of their heat through their face to the seat and 25% through their stem to the guide. Better thermal conductivity of the seat material is important in allowing the valve to cool itself. Elevated temperatures decrease fatigue life. Seat concentricity is another important issue. Valve seats distort thermally and mechanically during engine operation, and although the valve does conform to this distortion to a certain extent, the less conformation required by the valve the better. Compression and tensile stresses on the valve as it twists itself around to find the seat will eventually cause problems. Also, a tighter intimacy between the valve and seat will yield a cooler valve and a better sealing engine for more power.



SUGGESTIONS: Pay special attention to seat concentricity. Use beryllium - copper or copper alloy seats for both the intake and the exhaust side for best temperature conductivity.

7. TEMPERATURE PROFILE MAP
Through the use of “temperature check� valves, we have accumulated data on the actual operating temperatures experienced by the valve. These temperatures are not the same as exhaust gas temperatures ( EGT’s ). Valves typically run 150°F to 250°F less than EGT. Valve temperature can vary greatly depending on the type of fuel, combustion chamber design, spark advance, and compression ratio while the EGT remains constant. The accompanying graphic illustrates normal valve temperatures and exactly where they occur on the valve.



SUGGESTION: The display of elevated temperatures on the valve can be indicative of improper contact with the seat. When valve bounce occurs, seat contact becomes intermittent, disrupting the normal cooling event. Better and constant intimacy between the valve and the seat will lower temperatures, prolong life and improve power. Excellent valve springs improve intimacy and reduce bounce.

 

VALVE METALLURGY AND MANUFACTURING
VALVE FAILURE ANALYSIS: READING VALVE FAILURE MARKS
by TED TUNNECLIFF
Chief Engineer Aftermarket (Ret.)

Brief Introduction
by Henry D. Manley III

Ted Tunnecliff is the most knowledgeable man I have ever met in the field of engine valve metallurgy and manufacturing. Much of what I know about engine valves Ted generously taught me.

About seven years ago Ted was asked by Eaton Corporation to write a series of articles about valves. The most interesting of these fifty some articles to me was the group dedicated to failure analysis. How better to help Manley customers save their engines from catastrophic failures than to understand what can cause a valve to fail and then pass along that information.

I am delighted and proud to reprint, with Ted's and Eaton's permission, these articles in the hope that through increased knowledge racers and enthusiasts can long enjoy their modified engines trouble-free.


--------------------------------------------------------------------------------

Reprinted from Eaton Corporation's The Valve Event
Eaton Valve Engineering Notes and Topics
May 1995 - Issue 10 - Volume 3

VALVE FAILURE ANALYSIS:
READING VALVE FAILURE MARKS

BACKGROUND

This will be the final article in the series on valve failure analyses. In this issue we're going to discuss the various types of tattle-tale marks that can be seen on a valve and that can provide clues as to what may have caused a failure.

Not only do the failed surfaces themselves give us information on possible causes, but every place the valves touch another part during operation has the potential for showing us a cause of failure. That means the valve tip, keeper groove area, stem and seat face may have something to show us if we look carefully. One of the most important things that should be done in any valve failure analysis is to look in detail at every area of the valve before drawing conclusions.

TIP CONTACT MARKS

Most valves rotate at some time during their operation. Some rotate almost continuously and some sporadically. Many may not rotate at all or they may oscillate rather than rotate. We won't get into all the reasons they do or don't, but we do want to know if they did. That fact could be important in an analysis of the failure.

If you look closely at the valve tip you can usually see a contact pattern produced by the rocker pad as it moves back and forth across the tip during operation. A valve that has rotated well during operation will display a multiple rocker pattern and or concentric rings. A contact pattern on a valve that did not rotate but did oscillate is sometimes called a "bow tie" because of its resemblance to a bow tie. The type of pattern that is produced on the valve tip if the rocker pad and tip are not square with each other or if the pad and tip are not properly aligned is off to one side. Referred to as "side loading".

The implications are that poor rotation can cause seat leakage and guttering or excessive rotation can add to a seat a face wear problem. Misalignment can aggravate guide wear and possibly induce valve head fractures.

KEY CONTACT MARKS

Most valve keys are made of a strip of steel which has been formed to a cross section that will fit into the valve keeper groove. This strip is then rolled up and cut off to form a single key. The rolling-up process does not usually produce a perfect arc. If examined very carefully that arc looks more like a series of short, straight lines. Because of this the key, when installed on the valve, will touch at only certain high points - typically at only two. As long as these marks show no indication of circumferential motion, this should be considered a normal condition. However, if the contact marks have lateral lines through them, that would indicate that the keys were moving around the valve stem. Remember that the valve, keys and the spring retainer should be moving together as a single unit so that there should be no relative motion between these components as they move up and down with the valve. If there is circumferential movement of the keys, it means that the valve gear has been separating. That, in turn, means that the valve has not been following the cam contour and that its velocity as it seats could be much higher than designed. High seating velocity means high stress and the possibility of fractures of the valve head, head/stem blend or keeper groove areas. All that from just looking at the key contact marks. Neat, huh!

STEM CONTACT MARKS

As a valve moves up and down in the guide it will lean a little ( the stem to guide clearance ) one way or the other. As it leans, this causes a slightly heavier load on one side of the guide at the tip and on the opposite side at the bottom. If the valve is rotating as well as moving up and down, that slight sideways load will produce a burnishing of the stem all the way around it at both ends of the guide travel ( the valve lift ). The burnishing should be considered a normal condition as long as there is no indication of guide material pick up. If a lot of guide wear has taken place, that wear is usually at the hot end of the guide but not always. It depends to a large degree on what caused the wear. For example, if it was caused by distortion of the guide itself, it may wear primarily in one plane. That is, at one side at the guide bottom and the opposite side at the top. You could expect to see that type of pattern on the stem of a valve if it had not been rotating. Adhesive wear called "guide metal pick up" or "galling" occurs if there is not adequate lubrication, too tight clearance between the stem and the guide or a poor quality cast iron used in the guide.

SEAT FACE CONTACT MARKS

When a valve is not seating tightly due to a build up of combustion deposits guttering ( or burning or leakage ) takes place. Such deposits can chip away leaving a channel for exhaust gas leakage followed by the formation of corrosive gutters.

Indentations may be discovered after a valve is carefully cleaned of deposits filling pits making them look like corrosion pits. This is indentive wear which can be caused by combustion deposits embedded into the valve face while on the seat. This is a perfect example of why high temperature hardness is an important characteristic in valve alloys. The higher the valve material hardness, the more it will resist such indentations.

 

Reprinted from Eaton Corporation's The Valve Event
Eaton Valve Engineering Notes and Topics
January 1995 - Issue 6 - Volume 3

VALVE FAILURE ANALYSIS

BACKGROUND

Recently it was suggested that we provide some insight into valve failures. What causes them? What should be done to avoid them? It may sound pretty straight forward, but we are talking about a truly complex subject. Instead of trying to deal with this in one issue, we think it would be more effective to break the subject into small pieces and write an article about each of them. In this issue, we are going to explain some of the types of valve failures. In future issues, we will get into detail on each one.

BREAKAGE

When a valve breaks it can break at the head, in the stem or in the tip area. The head can fracture in a radial ( like a pie-shaped piece breaking out ), a chordal ( a half-moon shaped piece breaking off ) or a circumferential direction. These failures can be the result of excessive temperature, excessive loading, some manufacturing defect or a combination of these. Similarly, a stem fracture can take place in a number of ways and from a number of causes. Of course that is also the case in tip area fractures.

To give you a better idea about how complex this subject is, there are two different types of fractures no matter where they occur; impact and fatigue. As the word implies, impact is a sudden, generally one blow fracture, but fatigue can progress rapidly or very slowly.

In analyzing breakage, a clear fracture surface is very important in order to tell where it started. This may give us a clue about why it started. So handle with care. If you clean the part for gosh sakes don't use a wire brush! You can destroy a lot of valuable clues that way. Clean with a solvent or alkaline cleaner. Ideally, an ultrasonic cleaner works the best. Also, don't disturb other areas of the valve if it can possibly be avoided. These areas may give us clues as to why the fracture at the opposite end took place.


CORROSION

Like breakage, corrosion can happen in various areas of the valve and can be caused by several different things. Oxidation is a common type of corrosion. When the fence wire corrodes and breaks, we say it was caused by rust. That is true because rusting is a form of oxidation. Most, but not all, valve alloys are resistant to oxidation. The higher the temperature goes the less resistant they are to oxidation. So the head of a valve is more likely to oxidize than is the tip end. Similarly, if the head corrodes from oxidation it will be more apparent in the center of the head because it runs hotter than do the outer edges.

In diesel engines, sulfidation or sulfur corrosion is not too uncommon. Because diesel fuels tend to have considerably more sulfur in them than gasolines, valve alloys used in diesel engines are designed to resist sulfidation particularly when used in exhaust valves. Sulfidation, like oxidation, is more severe at higher temperatures than at lower ones. Vanadium pentoxide is another corrodent that can occur in low grade diesel fuels. It can be very destructive, particularly if temperatures are very high.

One corrodent we haven't mentioned yet is lead oxide. It is formed as a deposit on the valve and comes from the combustion of tetraethyl lead ( TEL ) in the gasoline. Since leaded gasolines are almost a thing of the past, we won't spend much time talking about this. We will simply point out that TEL was added to increase fuel octane ratings and was very corrosive. We should also say that although corrosive, it also acted as a lubricant between the valve and its seat, there by, preventing or reducing wear at that interface.

WEAR

In valves, wear can occur at the seat face, stem, or on the tip. In our experience seat face wear is the most common. Rarely do valve stems wear. The guide perhaps, but rarely the valve stem. Wear at the valve tip is also not very common these days.

There are generally three types of wear that can occur, adhesive, abrasive and corrosive. A fourth type, which is not truly wear, is indentive. Indentive "wear" usually takes place at the valve seat as pitting. If the pits seen are actually indentations then no metal has been lost so technically we shouldn't call it wear. If that pitting has removed metal then it is corrosive wear. Abrasive wear is very rare because it requires abrasive particles, which, unless the engine has been ingesting sand, something like that ordinarily doesn't take place. Combustion deposits do not cause abrasive wear. They are very soft and not abrasive.

The most common wear takes place at the valve seat face and occurs as adhesive wear. Adhesion is a transfer of metal from one surface to another through microscopic welding. Welding requires metals to be melted and that is what happens at the valve to seat interface as a result of pressures on the tiny surface asperities of the two parts. Welding also requires a clean surface to permit that direct metal to metal contact. As mentioned earlier the presence of lead in gasolines prevented much of the wear we are seeing today because it formed a layer of lead oxide on the two surfaces.


Preventing or reducing adhesive wear can be done by the use of high hardness or non-weldable materials, such as carbides, in the microstructure of the valve seat face and/or the seat insert. The nickel based Eatonites and cobalt based Stellites are examples of such alloys.

There is one other type of wear that we should mention and that is compressive fatigue. It is the type of wear that typically occurs on the valve tip. The mechanism is one of very high loading which creates a compression in the metals at the interface. Remember, stress at the valve tip/rocker pad line contact can easily be 120,000 psi or higher. The repeated compression loading and relaxation as the valve closes causes fatigue - or tiring out - of the metal. Eventually the metal fractures in small areas and pieces begin to fall out so that the appearance is one of pock marks or pitting.

Are you still with me? I told you failure analysis was an involved subject. Well, I think I've leaned on you enough this time so I'll sign off for now.

 

Reprinted from Eaton Corporation's The Valve Event
Eaton Valve Engineering Notes and Topics
February 1995 - Issue 7 - Volume 3

VALVE FAILURE ANALYSIS: BREAKAGE

BACKGROUND

This will be the second in the series of articles on valve failure analysis. You'll recall that last time we tried to give an overview of valve failures in general. This time we'll get into more detail on one type: Breakage.

VALVE BREAKAGE

When a valve breaks in an engine it usually breaks due to a failure mode we call fatigue. But it can also break by impact. The nature of the fracture surface, assuming it's not all battered up, will usually tell us which type it is.


FATIGUE FRACTURES

When a metal part is repeatedly loaded and unloaded as a valve is when it opens and closes, it can get tired - fatigued - if the conditions are too severe. By conditions we mean the combination of temperature, stress and corrosive environment. If any of these conditions are excessive, the valve will break at its weakest point. Of course, if we run it long enough, it will fatigue even under normal conditions. However, if it has been designed properly with all of the right alloys, heat treated correctly, and with the correct dimensions and finishes, it will last through the warranty period and then some.

Tests are run on the various alloys to determine just how much a particular material with a given heat treatment will take before it breaks. That is the number of cycles to failure, and we're talking about 10's or 100's of millions at a certain temperature and stress. This is called the endurance limit and is used to decide if the alloy is appropriate for a given application.

Let's get back to the fracture itself. A fatigue fracture has two zones: The area where the fracture began and progressed over some period of time and an area that broke suddenly because the unbroken material was so small it could no longer support even a light load. These areas look very different from one another. The best way to look is with good light and some magnification. The fatigue propagation zone will have a series of very fine concentric rings which begin at some point at the surface and get larger in diameter as they progress across the section. The outer area will have an irregular roughened surface with no particular pattern or character to it.

If there is only one fatigue initiation site visible, that is, only one set of concentric rings apparent, then the fracture started at only one point. That point could have been a defect on the surface or merely the point where the load was highest for some unknown reason. If there are a number of fatigue initiation sites then this implies that the part was overloaded. Fractures through valve keeper grooves usually look like this when the valve has been seating too hard.

IMPACT FRACTURES

If you were to take a piece of hardened steel, like the stem of a valve, put it in a vise and whack it real hard with a big hammer, it would break. ( If you try doing this, put a shop rag over the part so it doesn't nail somebody when it breaks off ). If you look carefully at the fracture you'll usually see two characteristics: One is a series of vague radial marks starting at the point where the fracture began and the other is a step-like change in contour called a shear lip.

FRACTURE INTERPRETATION

So what's the difference - which kind of fracture is it? Well. Probably one of the most important things you can learn is whether the fracture you're looking at was primary or secondary. A fatigue fracture takes some time to occur, so if you see one you can be pretty sure it was the place where the fracture started. An impact break is usually a secondary fracture that took place because the valve may have dropped down into the cylinder of a running engine and was hit by the piston which caused it to break. If we're trying to solve a problem we need to first understand it, then we can look for possible causes.

 

Reprinted from Eaton Corporation's The Valve Event
Eaton Valve Engineering Notes and Topics
March 1995 - Issue 8 - Volume 3

VALVE FAILURE ANALYSIS: CORROSION

BACKGROUND

Last month's article was on valve breakage. This month we're going to talk a little about valve corrosion. Once again it's not a simple subject, but we'll try to keep the exotic language to a minimum. Also we'll be talking primarily about exhaust valves for obvious reasons.

VALVE CORROSION - WHAT CAUSES IT?

Corrosion is a reaction between the metal of the valve and some corrodent. It can occur anywhere on the valve so we'll try to deal individually with each area. Before we do, let's talk about the corrosive mechanism itself.

First, it is a reaction, as we said, and something is needed to attack or corrode the metal. There are various things that will do this, but the main one is oxygen. Others include sulfur, vanadium pentoxide and lead oxide. These are the biggies in reciprocating internal combustion engine corrodents.

Oxygen is necessary for combustion of course, so we can't get away from it. We therefore use metals in valves that have been found to resist oxidation. Alloys that are high in chromium are best for the purpose. Nickel also adds to corrosion resistance, but chromium is number one. The oxidation that takes place produces an oxide on the part surface. That oxide can take various forms depending on what metal the oxygen is combining with. It can be loose and flaky as the rust ( oxide of iron ) on a piece of fence wire or thin and tight as the protective layer is what forms on stainless steel ( chromium oxide ). Also, high temperatures accelerate corrosion. Generally the higher the temperature, the faster the rate of oxidation or corrosion from other corrodents.

Sulfur can be a real bear as a corrodent in diesel engines because diesel fuel can be quite high in sulfur. Good quality diesel fuel can be as low as 0.1 to 0.5% as purchased for highway trucks in the U.S. It can also contain 3.0 to 6.0% sulfur if the engine is powering a piece of earth moving equipment that is building a dam somewhere in Africa. Sulfur in gasoline is generally 0.1% or less so sufidation corrosion is not a problem in gasoline engines.

Vanadium pentoxide is also sometimes found in low grade diesel fuels and can be even worse than sulfur. Lead oxide comes from the burning of gasolines containing tetraethyl lead ( TEL ). The TEL is added to gasoline to improve its octane rating. In many states in the United States leaded fuel is hard to find but I was surprised to see, some of the Western states are still selling it very openly. ( 1995 ) Lead oxide attacks or corrodes valves, particularly if their silicon content is over 0.25% that is the reason 21-4N ( EMS 10 ) and 21-2N ( EMS 222 ) have very low silicon contents.

IMPACT FRACTURES

If you were to take a piece of hardened steel, like the stem of a valve, put it in a vise and whack it real hard with a big hammer, it would break. ( If you try doing this, put a shop rag over the part so it doesn't nail somebody when it breaks off ). If you look carefully at the fracture you'll usually see two characteristics: One is a series of vague radial marks starting at the point where the fracture began and the other is a step-like change in contour called a shear lip.

HEAD FACE CORROSION

Let's start at the combustion surface of the exhaust valve and then deal with the seat face, throat area, stem and tip areas. The valve head face, at the center, is generally the hottest area of the valve and therefore the most susceptible to corrosion. As you go toward the head O.D. it tends to cool down because of the seat contact pulling the heat out. Remember, over 70% of the heat in the valve is transferred to the cylinder head through the seat contact area. That center area can run as high as 1500° F and can corrode very quickly. A neat little trick you can use in looking at a valve that has come out of an engine is to scrape some deposits from the center of the head onto a piece of paper. Then put a magnet under the deposits on the paper. If they are magnetic you can bet that the valve corroded there because of deposits from the combustion process itself ( fuel and oil ) are not magnetic. Those from an iron based alloy valve, even if it is a non-magnetic austenitic steel, will be magnetic, It's not always necessary to have a lot of expensive lab equipment to learn some of the fundamentals in failure analysis.

SEAT FACE CORROSION

As we mentioned earlier, the seat face area conducts the most heat out of the valve and is therefore generally cooler than the center of the head face. It assumes that the seat face is in full and proper contact with the cylinder head seat. Unfortunately that is not always the case. If the valve is not in full contact due to deposits, seat distortion, insufficient use, or some other cause, the seat face can get hot enough to corrode. If deposits or distortion are present the seat area may not seal locally and the leakage that will occur can corrode ( or "Burn" or "Gutter" ) the valve seat face and sometimes the cylinder head seat.

THROAT CORROSION

This is most common on spark ignited ( gasoline, propane, natural gas, alcohol, etc. ) engines because their exhaust gases are hotter than compression ignited ( diesel ) engines. With those hot exhaust gases comes the heating up of the valve throat and corrosion. The nature of this corrosion is very similar to that present on the combustion face.

STEM CORROSION

As you move away from the throat and up the valve stem the temperature and the susceptibility to corrosion drops. Inside of the guide contact area the temperature drops drastically ( perhaps 1000° F in three-fourths of an inch ) as does the chances of corrosion. If an engine has set for an extended period of time and the valve stem is not some type of stainless steel, you may get rusting of that area.

KEEPER GROOVE AND TIP

Once again if the valve is not a stainless steel or similar alloy, the tip and keeper groove areas can rust. Other than that, there is little chance that corrosion will take place here.

Hope you didn't get too bored wading through this one. See you next time!

 

Reprinted from Eaton Corporation's The Valve Event
Eaton Valve Engineering Notes and Topics
April 1995 - Issue 9 - Volume 3

VALVE FAILURE ANALYSIS: WEAR

BACKGROUND

In last months issue we talked in some detail about valve corrosion as a failure mechanism. This month we're going to discuss wear and this is a real can of worms. What we'll try to cover is the various types of wear, and how to recognize them, and some approaches in trying to avoid or correct them. Wear is a very difficult subject, however, so we're not going to try to give you all the answers. Hopefully, we'll simply take some of the confusion out of the subject.

TYPES OF WEAR

There are several types of wear that can and does take place on valves:
Adhesive, abrasive, corrosive and fatigue.


ADHESIVE WEAR

One of the significant things about adhesive wear is that at the interface, or the point where it touches another metal surface, it must be very hot in order for the microwelding to take place at all. That is what adhesive wear is � microscopic welding. The heat produced at the contact interface is very high � near the melting point of the two metals touching each other. Where does all that heat come from? Good question. Believe it or not, it comes mostly from the stress of contact � not from the temperature of the environment. Sure, part of it is from exhaust gas temperatures, but adhesive wear can be just as destructive on an intake valve which is obviously a lot cooler.

In order to understand this better, it helps to think of it as viewing it through a microscope and in slow motion. The tiny points of metal sticking up, remember nothing is perfectly smooth � contact similar points on the other part and as seating of the valve continues, these points come under very high stress because they are initially carrying all the load. The rubbing of these points over one another is what creates the high surface temperature. Also each time the valve seats, it has moved slightly so no new points, or asperities of the mating parts, are touching each other. That roughened surface is the result of the microscopic welds being torn apart as the valve and seat separate.

As proof of the high temperatures created, we have noticed in adhesive wear photos magnified from 100X - 1000X, that the metal structure immediately beneath the surface is leaning sideways. That suggests that those very hard carbides ( compounds of metals and carbon ) have been bent by the wear mechanism which in turn says that this thin layer right at the surface must have been very hot.

ABRASIVE WEAR

Now let's compare the adhesive with the abrasively worn surfaces. On the abrasive specimen the surface shows a scratched appearance from hard particles digging into it as they were moved across the surface. In this case, those hard particles were grit introduced between the two specimens in contact with each other during the test. But in a valve and seat operating in an engine where does the grit come from? Another good question.

One possible source can of course be a poor air cleaner allowing grit from the air to get into the engine. A more likely possibility, however, is the worn parts themselves. Remember what we said about carbides? They are compounds of carbon and certain metals such as iron, chromium, tungsten, molybdenum and some others that are called "carbide formers". These carbides are present � and we want them to be there to help resist wear � but they can also cause it. The carbides are discrete particles within the structure of the metal and as wear progresses, they can fall out due to the softer matrix material being worn away around them. When they fall out they become the grit which produces abrasive wear.

We have over simplified some of this to make it clearer. Usually you won't see nice, neat specimens of adhesion and abrasion. You will probably see something that is a combination of several wear modes and not as easily pinned down.

Also note that in an abrasive wear specimen the carbides beneath are standing up nice and straight. No indications of heat softening and bending the structure beneath the surface as was the case with the adhesive wear specimen.

CORROSIVE WEAR

This one is not quite as neat as adhesive and abrasive wear. That's because any products produced by the corrosion of a surface are usually carried away when the two parts come together which breaks them loose and they are then swept off by the exhaust gas or air stream. If pits are formed on the worn surface it can very well be from corrosion unless they are simply indentations. Logically, we know corrosive wear must take place even though it can be difficult to prove. We can see the formation of surface compounds from the corrodents in non-worn areas and we know some of the properties of these compounds are high hardness and brittleness.

COMPRESSIVE FATIGUE WEAR

Sometimes when the tip of a valve wears it is caused by compressive fatigue. It appears as an irregularly pitted pattern on the tip if you catch it early enough. The mechanism goes something like this: The rocker arm pad on the valve repeatedly exerts a force beyond the compressive strength of the metal and it yields slightly. That portion directly under the pad contact line moves straight down, but a little deeper in the metal it moves sideways. That sideways motion is in tension rather than compression and repetitions of this loading can cause a microscopic crack to form beneath the surface. As more of these microcracks are formed, they join up and allow a small chunk to break away forming a pit on the tip surface and we call that compressive fatigue wear.

AVOIDING WEAR

This one really gets hairy. Obviously the materials and heat treatments that are used for valves have been well proven long before they get into any application. But that is where the manufacturers control ends. The end user relies on the component manufacturer and the engine builder to do their jobs properly and he is rarely disappointed. The user has a responsibility too. Proper fuels, lubes, general maintenance and good operating procedures are all necessary to realize the best potential for performance, economy and durability.

So what component factors are the most influential in reducing wear? We've already touched lightly on many of them, but let's go a little deeper.

Hardness � probably the most important single material factor. It is measured both at room temperature for such areas as valve tips and stems, but also at elevated temperatures because of the high temperatures of exhaust valve heads. And remember hardness is a measure of both strength and of wear resistance.

Microfinish � remember the surface asperities we talked about? The rougher the surface the more susceptible those peaks of metal are to wear. If the metal is smoother, the load is spread out more and each point is not as stressed.

Corrosion � if the engine parts are exposed to abnormal corrodents they will corrode more quickly. For example, if the engine is designed to run on low sulfur diesel and you put some 6% garbage in it you can expect trouble. And you may be lucky if valve wear is the only problem.

You can't do a whole lot to avoid adhesive wear. That usually has to be done by the engine and the component designers, but abrasive wear you can help to control. Keep the air cleaner changed regularly and more frequently if your are operating a lot in dusty country.

Compressive fatigue � design is paramount but you can help by not overspeeding the engine which puts a lot of extra load on the valve tip and can accelerate wear.

 

Reprinted from Eaton Corporation's The Valve Event
Eaton Valve Engineering Notes and Topics
May 1995 - Issue 10 - Volume 3

VALVE FAILURE ANALYSIS:
READING VALVE FAILURE MARKS

BACKGROUND

This will be the final article in the series on valve failure analyses. In this issue we're going to discuss the various types of tattle-tale marks that can be seen on a valve and that can provide clues as to what may have caused a failure.

Not only do the failed surfaces themselves give us information on possible causes, but every place the valves touch another part during operation has the potential for showing us a cause of failure. That means the valve tip, keeper groove area, stem and seat face may have something to show us if we look carefully. One of the most important things that should be done in any valve failure analysis is to look in detail at every area of the valve before drawing conclusions.

TIP CONTACT MARKS

Most valves rotate at some time during their operation. Some rotate almost continuously and some sporadically. Many may not rotate at all or they may oscillate rather than rotate. We won't get into all the reasons they do or don't, but we do want to know if they did. That fact could be important in an analysis of the failure.

If you look closely at the valve tip you can usually see a contact pattern produced by the rocker pad as it moves back and forth across the tip during operation. A valve that has rotated well during operation will display a multiple rocker pattern and or concentric rings. A contact pattern on a valve that did not rotate but did oscillate is sometimes called a "bow tie" because of its resemblance to a bow tie. The type of pattern that is produced on the valve tip if the rocker pad and tip are not square with each other or if the pad and tip are not properly aligned is off to one side. Referred to as "side loading".

The implications are that poor rotation can cause seat leakage and guttering or excessive rotation can add to a seat a face wear problem. Misalignment can aggravate guide wear and possibly induce valve head fractures.

KEY CONTACT MARKS

Most valve keys are made of a strip of steel which has been formed to a cross section that will fit into the valve keeper groove. This strip is then rolled up and cut off to form a single key. The rolling-up process does not usually produce a perfect arc. If examined very carefully that arc looks more like a series of short, straight lines. Because of this the key, when installed on the valve, will touch at only certain high points - typically at only two. As long as these marks show no indication of circumferential motion, this should be considered a normal condition. However, if the contact marks have lateral lines through them, that would indicate that the keys were moving around the valve stem. Remember that the valve, keys and the spring retainer should be moving together as a single unit so that there should be no relative motion between these components as they move up and down with the valve. If there is circumferential movement of the keys, it means that the valve gear has been separating. That, in turn, means that the valve has not been following the cam contour and that its velocity as it seats could be much higher than designed. High seating velocity means high stress and the possibility of fractures of the valve head, head/stem blend or keeper groove areas. All that from just looking at the key contact marks. Neat, huh!

STEM CONTACT MARKS

As a valve moves up and down in the guide it will lean a little ( the stem to guide clearance ) one way or the other. As it leans, this causes a slightly heavier load on one side of the guide at the tip and on the opposite side at the bottom. If the valve is rotating as well as moving up and down, that slight sideways load will produce a burnishing of the stem all the way around it at both ends of the guide travel ( the valve lift ). The burnishing should be considered a normal condition as long as there is no indication of guide material pick up. If a lot of guide wear has taken place, that wear is usually at the hot end of the guide but not always. It depends to a large degree on what caused the wear. For example, if it was caused by distortion of the guide itself, it may wear primarily in one plane. That is, at one side at the guide bottom and the opposite side at the top. You could expect to see that type of pattern on the stem of a valve if it had not been rotating. Adhesive wear called "guide metal pick up" or "galling" occurs if there is not adequate lubrication, too tight clearance between the stem and the guide or a poor quality cast iron used in the guide.

SEAT FACE CONTACT MARKS

When a valve is not seating tightly due to a build up of combustion deposits guttering ( or burning or leakage ) takes place. Such deposits can chip away leaving a channel for exhaust gas leakage followed by the formation of corrosive gutters.

Indentations may be discovered after a valve is carefully cleaned of deposits filling pits making them look like corrosion pits. This is indentive wear which can be caused by combustion deposits embedded into the valve face while on the seat. This is a perfect example of why high temperature hardness is an important characteristic in valve alloys. The higher the valve material hardness, the more it will resist such indentations.

 

Recieved a call from Jesse at Manley Performance this morning. The news was great. The exotic metal exhaust valves are finished. They will be sending them directly to HP Coating. We finally have all the parts. HPC should have the valves coated abd back in our possession in two weeks.

This means Killer Angel will definitely be operational by the end of September.

Sharkey, get the Black Mamba ready. I'm having Rob build a cage and fit a chute to KA just to give you an idea where I believe we will be.

 

Chad, I'm getting excited! I hope it all comes together well and the tuning goes smoothly. This will be quite amazing if it all finally materializes. It's like waiting for the final episode of a made for TV mini-series! A few more weeks and it's test time. You must be getting a little nervous about the maiden voyage!

Mike

 

Mike,

It is hard to believe that we have all the parts and are now simply awaiting for the springs and exhaust valves to be coated.

Once everything is here it will take about two weeks to assemble the motor and install.

Nervous ................ you betcha.