To realize optimal performance, maximize airflow around the valve so air/ fuel mixture quickly enters the combustion chamber, efficiently burns, and then expeditiously exits the cylinder. This chapter delves into the intricacies of optimizing the valve and valve parts for your particular setup. The valves and related valvetrain hardware need to precisely match one another from cylinder to cylinder, but these parts must also meet the performance standards you’re targeting. The valves required for a race engine are far different than valves required for a street engine.
This Tech Tip is From the Full Book, MODERN ENGINE BLUEPRINTING TECHNIQUES: A PRACTICAL GUIDE TO PRECISION ENGINE BUILDING. For a comprehensive guide on this entire subject you can visit this link:
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When inspecting a used valve (assuming you’re considering placing it back into service), check valvestem diameter in three locations: about 1 inch below the tip, at the center of the stem length, and at the lower area of the stem (about .500 inch above the throat and/ or undercut). If you note any difference in stem diameter among these three measurements, discard the valve.
Check each valve for runout or bending. If a valve has more than .001 inch runout, don’t use it. Don’t even think about trying to straighten it out. Runout can be checked by placing the valve on a small pair of V-blocks or by fixturing it onto a dedicated valvestem runout tool.
Monitor runout with a dial indicator while slowly rotating the valve. Also check the valve for concentricity, which is the valve head in relation to the centerline of the stem. Stack-ups in runout and concentricity variation prevent optimum sealing at the seat, and under high-RPM use, this can also lead to eventual valve failure (as in the head snapping off the stem)
Also inspect all valves for cracks/ faults. A visual inspection may enable you to find surface cracks (at the valve face areas and the entire valve head as it tapers to the stem). Surface-flaw checks can be performed with magnetic particle inspection or with a dye penetrant system. In order to find cracks that are below the surface, an ultrasonic inspection station is useful. Inspection of exhaust valves is particularly important due to the metallurgical stresses experienced by exhaust heat.
Depending on the type of valve, it may or may not be reconditioned by regrinding the faces. Some valves originally had a specialized treatment, such as diamond-like coating (DLC), that provides a harder surface. You aren’t able to regrind without ruining this coating, but you can always send the valves back to the manufacturer for retreatment. However, if the valves are far enough gone to require refacing, you may as well replace them (if the application involves racing.
Valve refacing (seating face) can be done by a refacing machine with a collet or chuck or by centerless grinding. A facing machine has a collet or chuck that secures the stem and the valve is spun against the grinding wheel to create fresh face angles. This secures the valve within a tolerance range that should be .0005 inch or less.
Centerless grinding eliminates the collet or chuck. Instead, the stem is secured along most of its length, rotating the valve on its own centerline (this eliminates any variables of runout on a chuck and spindle). The valvestem is secured in a pneumatic support. Canted rollers feed the valve against a precision stop. The valve spins against the spinning grinding wheel. Theoretically, centerless grinding is much more accurate, although advances have been made with collet machines that now rival the precision of centerless grinding.
However it’s achieved, the goal is to grind the valve face while eliminating runout. I do not delve too deeply into reconditioning valves here, because the discussion throughout this book focuses more closely on high-performance and racing applications, rather than individual component reconditioning.
Valve seats (in the finished form) are responsible for three basic functions: to provide a seal at the closed-valve position, to promote optimum airflow when the valve opens, and to help transfer heat away from the valve head when the valve is closed. The seats need to be hard enough to last a reasonably long period, soft enough to prevent damaging the valve, and offer enough heat transfer to prevent burning the valve.
The location height of the valve seats in the cylinder head is critical to achieve consistent valve-to-piston clearances and uniform combustion chamber volumes. When your goal is to blueprint an engine, this is part of the task. With the valves installed to the head (minus springs) and the head upside-down on a bench, a valve depth checking gauge can be used to determine the distance between each valve face and the head deck.
Uneven installed valve depths can be corrected by cutting the problem seats a bit deeper or replacing the seat(s) and recutting to move the valve closer to the deck. If you don’t pay attention to this, you may think (on paper) that your compression ratio is, say, 11.25:1. In fact you may have chambers that range from 11.15:1 to 11.37:1, for example.
Every time the cylinder heads are freshened up (reconditioned), the seats are recut and the valves sink deeper into the port areas. By the same token, every time the deck surfaces are “kissed,” the valves move closer to the combustion chambers. Recutting the seats results in sharpening the short-side radius of the port, slightly hindering flow. Moving to large-diameter valves, and/or replacing seats with new seats tends to improve flow because you’re moving the valve closer to the combustion chamber and allowing a softer radius. A variety of seat materials are available, including beryllium copper, ductile iron, stellite, chromium, nickel alloy, cobalt, and powdered metal.
Beryllium-copper seats are commonly recommended with titanium valve locations. This alloy seat material has about 98-percent copper and provides decent heat transfer and holds up to severe valve closing pressures.
Beryllium copper offers better heat-transfer performance than, say, bronze or iron. Recently, copper-nickel alloy seats have been developed that cool as well as, or sometimes better than, beryllium copper. This has been done in large part due to health concerns about machining beryllium, which is considered a toxic material.
Some titanium valves have hardened faces to accommodate sintered-iron or bronze seats.
Titanium valves, though lighter in weight than stainless steel, tend to run hotter, so they need a seat that is able to pull heat away quicker.
Although PM seats are certainly acceptable for a variety of applications, they may not be the best choice for ultra-high-performance/racing use. Even though they allow the manufacturer to tailor the material for hardness and heat transfer capabilities, in some cases this type of valve seat tends to work-harden when cut, which sometimes makes recutting during servicing difficult.
If you’re rebuilding cylinder heads for high-performance or racing use, you’re better off by choosing ductile iron or nickel-copper, which is easier to machine and compatible with performance valve materials.
Multiple angles are common and a three-angle valve job is the most common for performance applications. The sealing angle refers to the contact between the valve head and the valve seat. This is usually a 45-degree angle. The top angle is located at the outer perimeter of the seat (the largest-diameter surface, closest to the piston). The bottom angle is the smallest-diameter surface, closest to the valvestem. It’s easy to get them mixed up. With the cylinder head in an upright (as installed) position, you might think that the “bottom” cut is closest to the head deck and piston.
The bottom cut serves two purposes: to provide less turbulent airflow transition and to reduce the width of the 45-degree sealing angle. The reduced width of the sealing angle promotes better airflow. (The bottom angle is often referred to as the throat angle.) The intake valve’s location and width of the 45-degree sealing angle is commonly moved, or biased, closer to the combustion chamber. Most exhaust sealing contact areas are generally placed in the middle of the 45-degree angle to aid in durability and to keep the contact a bit farther away from sharp edges, which otherwise could promote valve burning.
The two extra valve and seat angles have nothing to do with sealing the valve when closed. These angles are provided to promote improved airflow as the air/fuel mixture exits the valve pocket and transitions into the combustion area. Making this flow path smoother theoretically improves efficiency and minimizes air/ fuel flow turbulence. OEM valves and seats are usually cut with valve sealing as the priority, while aftermarket performance angles are considered to improve airflow in the pursuit of higher performance.
For racing applications, serious research has been invested to determine optimum specific angles and angle-cut widths. In many cases, this is closely held, top-secret data and you can understand why. An engine builder is reluctant or unwilling to share this info after investing hundreds of hours in research and development on the computer, in the lab, on a flowbench, and on the dyno.
As a result of trial and error and the availability of today’s computer-aided software and CNC machining capabilities, many race engine developers have taken advantage of as many as five (or more) angles in order to optimize airflow. This might involve a more drastic (steeper) top cut in the 35-degree range and a 50- to 70-degree undercut just below the primary seat. The best setup for a specific engine and specific application results from research and testing. It’s all about optimizing the airflow to best suit the particular RPM band, peak power, and torque needed for a given engine type and given track application.
Seat angle (where valve sealing occurs) is usually 45 degrees. A typical bottom cut (where the flow begins its path from the intake runner) may be at 60 degrees. A typical final angle may be 30 degrees. In many cases, the same angles are used at intake and exhaust locations, but the width of the valveto-seat contact (at the 45-degree angle) usually varies. Exhaust valves are usually fitted with a slightly wider contact area (say, .060 to .080 inch) than the typical .040-inch-wide contact at the intake valves in flat-tappet cam engines. Roller cams with higher spring pressures often require wider seat contact areas in the .060-inch intake applications and .080- inch contact widths in exhaust locations, to help prevent seat damage or “pounding out.”
This book focuses on performance and race spark-fired engines, but you should be aware that some Diesel engines have seat contact angles other than 45 degrees. Don’t assume that every engine uses a 45-degree seat. Although a narrower seat contact area generally flows better due to the heat transfer between the valve head and the valve seat), exhaust seat contact areas are usually wider to allow more efficient heat transfer, which aids in cooling the valves. An exception is the professional drag race engine application, for which the builder may take advantage of narrower seat contact widths to optimize airflow in these short-run applications, with durability taking a lower priority because these engines typically experience more frequent teardowns and freshening.
Performance Valve Technology
A variety of valve materials and designs are available for performance applications. This information is provided to help you make an informed decision.
Stellite is a hard coating applied to valvestem tips and faces to increase surface hardness and increase resistance to wear. This treatment is commonly used on stainless steel valves. In an effort to increase heat dissipation in exhaust valves, some valvestems are hollow and are partially filled with sodium. The sodium liquifies at about 200 degrees F, allowing it to travel up and down inside the valvestem, aiding in heat transfer.
Some valves have hollow, empty stems simply as a way to reduce weight. Hollow-stem valves are usually finely micro-finished on the inside of the stem to remove potential stress risers that might otherwise exist as a result of the drilling process.
Most high-performance stainless steel valves are manufactured as a onepiece forging, most commonly using a stainless steel material called EV-8. Highquality stainless-steel valves are also equipped with a welded-on hardened tip.
Titanium valves offer substantial weight savings and are best suited to engines that require quick acceleration and experience extended high RPM. Reducing valve weight reduces rocker arm wear and allows the use of lighter springs, which in turn reduces frictional loads at contact areas between the lifter and the cam lobe.
Titanium valves, while substantially more expensive than stainless steel valves, are typically about 45 percent lighter than steel or stainless steel valves of the same size. Titanium valves are a good choice where valvetrain weight needs to be reduced. Titanium valves are not pure titanium, but are a blend of copper and other alloys. The advantage lies in its excellent weight-to-strength ratio. The disadvantage involves higher cost and increased difficulty in remachining during valve service due to its tendency to gall when cut with incorrect cutting bits.
Although not considered a disadvantage, it’s important to know that titanium valves are relatively softer than other materials. As a result, the valve tip must be protected from rocker arm pressure. This is handled by adding a hardened-steel lash cap or by the application of a specialized hard coating at manufacturing. If you purchase titanium valves, the manufacturer should provide information relative to the need for lash caps.
If a titanium valve requires a hardened lash cap, the valve tip is usually coated with ceramic or other hard-surface coating in order to protect the titanium from the friction generated between the lash cap and the valve tip that could otherwise result in galling. Some titanium valves have a deep, diamond-like treatment that does not require a lash cap. Again, when using titanium valves, it’s critical to verify if lash caps are required.
The retainer lock groove is another area of concern with titanium valves. In order to address potential galling of the titanium, the groove area is treated with a specialized positive vapor deposition (PVD) coating. Some manufacturers warn against handling titanium valves with bare hands, cautioning that skin acids may affect the valve’s coating. A common recommendation is to wear latex gloves or to apply a light coat of oil to the valves before handling. If the titanium valve face is treated with a PVD coating, never use an abrasive lapping compound in an effort to enhance valve seating.
Additional cautions about titanium valves involve the valve seat material. Most titanium valves require a relatively soft seat material such as nodular iron or nickel-bronze; a too-hard seat material can quickly beat a groove into the valve face. However, some titanium valves are treated with chromium nitride to provide a hard protective surface, making them compatible with ductile-iron seats.
None of these issues should be regarded as titanium shortcomings, but you must be aware of the concerns if you plan to lighten valve weight with this material.
Nimonic 90 and Inconel
Other exotic valve materials include Nimonic 90 and Inconel. Nimonic 90 is a nickel-chromium alloy. Its claim to fame is its ability to withstand extreme temperatures and is sometimes preferred for nitro-methane and extremely high-boost-pressure turbocharged applications.
Inconel is a nickel-based alloy also designed for extremely high-heat conditions. It is suited for extreme-pressure nitrous and forced-induction race engine applications.
Valve coatings provide enhanced performance. The information that follows was provided by Del West Engineering and Xceldyne.
PVD occurs because of a physical reaction. Inside a vacuum-chamber plasma environment, metals are deposited via evaporation, sputtering, or arcing fragments of the metals that are physically moved onto the substrate. In other words, there is no chemical reaction that forms the coating onto the substrate.
Chemical vapor deposition (CVD) occurs because of a chemical reaction. The process exploits the creation of solid materials directly from chemical reactions in gas and/or liquid compositions or with the substrate material. The product of that reaction is a coating material that condenses on all surfaces of the part and inside the vacuum chamber plasma environment.
Diamond-like carbon (DLC) coating is a thin-film coating applied via a plasma-assisted chemical vapor deposition (PaCVD) process. This coating combines very low frictional resistance and extreme hardness. These coatings are used to reduce wear and friction for rapidly reciprocating components, where friction reduction is a primary goal. Common applications include finger followers, tappets, and piston pins.
Chromium nitride is a thin-film coating also applied using a PVD process. A cathodic arc is discharged at the target to evaporate the chromium into a highly ionized vapor, which is done in a partial pressure of nitrogen inside a nitrogen tank. This method deposits chrome onto the stem. This provides a higher level of adhesion than the PVD sputtering method in which a glow-plasma discharge bombards the material and converts some material into a vapor. This process is commonly used for titanium, steel, and nickel valves.
Thermally sprayed coatings can provide thick coatings over a large area at a higher deposition rate than other coating processes such as PVD or PaCVD. These are coatings that include plasma spraying and high-velocity oxygen fuel (HVOF) spraying; they are widely used to protect valvestems and tips.
Thin-film coating options such as chrome nitride, titanium aluminum chrome nitride, diamond-like carbon, and amorphous silicon carbide are used during the valve design process based on the suitability of the coating properties for the specific engine application and historical post-engine teardown feedback and analysis.
In certain applications, a combination of coatings may be used on an individual valve.
For example, the “ductile” properties of a chrome nitride coating (hardness 1,600 HV) is selected for application to the valve tip, while the low-friction attributes of a diamond-like carbon or amorphous silicon carbide coating (friction coefficients .1 or less) is chosen for application to the critical valve-seat head region.
Low-friction and inert thin-film coatings are compatible for dry fuels, which include low-sulphur content or alcohol-based fuels. The application of a coating on the valve head and valvestem can be considered as a solid lubricant, minimizing adhesive wear between the valve-seat or valve-guide interface. Adhesive wear, also known as scoring, galling, or (worse case) seizing, results when two solid surfaces slide over each other under pressure. Surface projections, or asperities, plastically deform and eventually weld together under the high localized pressure. As sliding continues, these bonds break. This creates cavities on one surface and projections on the other. Tiny abrasive particles can also form, causing additional wear.
Specific to applications associated with excessive exhaust gas temperature, hybrid coatings (platinum-, palladium-, or niobium-based) have been examined as a means to retard embrittlement of the base titanium material. The idea is to minimize the ingress of oxygen through the coating and represent novel strategies to yield robust coatings for ultra-high temperature environment applications.
Valvesprings are critical engine components that must be matched to the rest of the valvetrain components. If one fails, there is potential to destroy an entire engine by “dropping a valve.” There is a wide variety of valvesprings available today to suit most applications; single, dual, triple, and beehive. They are defined by ID/OD, with or without dampener, installed height, seat load, open load, coil bind, natural frequency, and rate.
Engine valvetrains must be viewed as a system. Valvesprings are the control mechanism for the system, and are measured in linear force (in-lbs) or load, not pressure (lb/in2) as sometimes referred to.
In a typical pushrod V-8 engine, the valvetrain system for one valve consists of the cam profile, lifter, pushrod, guide plate, rocker arm, rocker arm stud, valve, valvespring, valvespring retainer, valvestem locks, valveguide, valvestem seal, and valve seat. All of these components must work together to balance the forces in the valvetrain system.
Valvesprings must balance or counteract the forces in the valvetrain system, and keep all system components in contact with one another. These forces are created by the masses of the moving components of the system. Too little valvespring control force and the components of the system become unstable and out of control (valve float). In contrast, too much valvespring control force wastes mechanical energy and could overstress the components in the system, causing them to fail. The goal is to minimize component mass, yet maintain enough strength for the applied loads, and to use valvesprings with the appropriate control force.
Most performance aftermarket camshaft manufacturers recommend spring specifications for a particular cam profile. In most cases these recommended spring specifications were found by taking an average of generally accepted component masses and testing them in different load scenarios and RPM ranges. This ensures the natural frequency of the valvetrain system is tuned for the application.
Spring designs have evolved over the years. Traditionally, springs were made using round wire. In order to handle higher loads with more radical cams, double springs (an inner spring supplementing the outer spring) and triple springs (inner and outer along with an additional dampener spring) were developed. Although able to handle higher loads and speeds, this added more mass. Ovate wire, although more expensive, provide increased spring wire crosssection (allowing the creation of a stiffer spring in the same available space). Ovate wire isn’t round. It’s oval shaped with a bit of a teardrop, similar to the shape of a camshaft lobe.
Another method of providing necessary spring pressure while saving weight and space is to use “beehive” springs, which taper in diameter from bottom to top. This allows the use of small-OD retainers (which, in steel, may be as light as a large-diameter titanium retainer), which improves rocker clearance.
One advantage of the beehive design, aside from size and weight economy, is the tapered spring’s ability to better absorb harmonics, for increased stability. There is debate about the advantages of this design; some builders embrace the beehive design and others prefer constant-diameter dual springs. Although beehive springs may accommodate certain applications using solid or hydraulic flat-tappet cams or hydraulic roller cams, solid roller cams require heftier springs, with conventional double or triple springs preferred.
Altering rocker arm ratio also affects spring requirements. As you increase rocker arm ratio, a correspondingly stronger spring is needed. This is fairly easy to determine. The rule is to increase open spring pressure by the same percentage of rocker arm ratio increase. You can use this formula:
Percent of Change = (new ratio – old ratio) ÷ new ratio
For example, if you have 1.6:1 rockers, but you decide to swap to 1.7:1 rockers, the formula works like this:
1.7 – 1.6 = .1
.1 ÷ 1.6
.0625 x 100
So, in this case moving from 1.6:1 rockers to 1.7:1 rockers represents an increase of 6.25 percent. As a result, you increase the valvespring’s open pressure by the same amount. If the original springs had, say, 500-pounds open pressure, you need springs with an open pressure of 6.25 percent more, or 531 pounds.
It is important to check the coil bind of the valvesprings when increasing rocker arm ratios to determine if there is a clearance issue with any of the components. To calculate, use this formula:
Lift Increase = (cam lift ÷ old rocker arm ratio) x new rocker arm ratio
For example, a .550-inch-lift smallblock Chevy cam with 1.5 rockers changing to 1.6 rockers:
525 ÷ 1.5
.350 x 1.6
An increase of .010-inch valve lift
Similar to seating piston rings or breaking-in a flat-tappet cam, new valvesprings should be conditioned (broken-in) to aid in long-term spring life. During initial engine start-up, run the engine at 1,500 to 2,000 rpm until it reaches normal operating temperature. Shut the engine off and allow the springs to cool to ambient temperature.
Pocket clearance refers to the clearance between the ID of the spring pocket (where the spring rests on the cylinder head) and the spring’s OD.
Excess clearance allows the spring to move (dance) on the pocket, which leads to spring instability and causes wear at the bottom of the springs and the spring seat. A spring cup may be installed to register the spring OD. A spring locator may be used to register the spring ID. If there’s no clearance, the spring binds in the pocket, which places stress on the bottom coil, limiting the bottom coil’s ability to grow (via heat and compression).
The bottom of the retainer must fit the spring with a minimal clearance (generally .005- to .010-inch clearance to .001-inch interference. If it’s too tight, you apply too much stress to the spring. If too loose, you increase wear. If the springs have duals or triples, this applies to each spring as it mates to the retainer.
Along with spring fit, consider the connection between the retainer and the valvestem. This involves the valve locks (keepers). The installed outer angle of the keepers must match the inner taper of the retainer (7-degree lock with a 7-degree retainer, 10-degree lock with a 10-degree retainer, etc.). The traditional 7-degree design is often changed to the 10-degree style, which provides additional surface area to optimize load spreading.
Also, the ID of the keeper pair must match the valvestem diameter and the style of lock groove on the valve. The shape of the retention band inside the keepers must be compatible with the shape of the locking groove on the valve.
The majority of valves have a squarecut groove, with the keepers featuring a square-cut male rib. However, radiused (called bead lock) styles offer engagement with less-isolated stress points (radiused instead of sharp edges). Many titanium valves have a bead-lock design, due to the nature of titanium, which is very sensitive to stresses (nicks, sharp edges, etc.). The point is to be aware of the need to match the retainer and keeper sizes and designs to accommodate your valves and springs.
Spring Installed Height
Installed height refers to the dimension measured from the bottom of the spring retainer to the point where the top of the outer spring contacts the retainer to the spring pocket in the cylinder head when the valve is closed. Installed height affects spring tension, and is the determining factor for spring closed tension. Check your camshaft specification card. It lists the suggested spring installed height for that cam with the cam manufacturer’s recommended springs.
For example, if the card notes that a specific valvespring part number should be installed at 105 pounds at 1.700 inches, that means that if the spring is installed at a height of 1.700 inches, this should place 105 pounds of tension with the valve closed.
Altering the spring installed height directly affects tension. If spring installed height needs to be reduced, a shim may be placed under the spring. An alternative is to select a retainer with a deeper dish, or a different-style valve lock that changes the retainer location on the valve. Spring tension increases as installed height is decreased, and spring tension decreases if the installed height increases.
Spring Open Pressure
Valvespring open pressure represents the pressure (in psi) that’s placed against the spring retainer at maximum valve lift. The spring must provide sufficient pressure in order to control the lifters against the cam as the valve changes direction from opening to closing. Insufficient spring pressure causes the lifters to bounce over the cam lobe, which causes valve float. This can also lead to premature camshaft wear.
If valvespring pressure is excessive, the pushrods experience greater stress and are more likely to flex, which also leads to valve bounce. Heavier valves can handle higher spring open pressures, while lighter valves are better suited with lower spring pressures.
Spring Coil Bind
Valvespring coil bind occurs when the spring is compressed to a point where the coils touch each other during maximum lift. As mentioned earlier, you must check for coil bind. Using a valvespring checker press, coil bind can be measured by placing a retainer on top of the spring and carefully compressing the spring until the coils touch each other. The distance from the bottom of the retainer to the bottom of the spring is the coil bind height.
To calculate maximum spring travel, subtract the coil bind height from the installed height. Remember that spring travel must be at least .060 inch greater than the full lift of the valve. This safety margin is needed to prevent coil bind and overstressing the spring. If the coils bind, this creates a dead-stop during valvetrain operation, so something’s gotta give: pushrod bending, rocker arm breakage, lifter and/or camshaft damage, etc.
The easiest way to measure coil clearance (prior to assembly, that is) is with a bench-mounted spring tester. Install the valve into the cylinder head (remember to dedicate each valve to each valve location in each head. That way, once measured and clearanced, you know that the particular valve fits properly in a specific location. Don’t assume that you can mix up the valves). With the valve fully inserted into the (intake or exhaust) location, with the valve fully seated, install locks and the retainer. Pull up on the retainer and measure the distance between the underside of the retainer (where the spring contacts the retainer) and the spring seat. If you’re using hardened spring seats, be sure to install these seats for this check.
Place the spring on the tester and compress to the spring’s installed height. The pressure tester displays the seat pressure at that installed height.
Then determine the maximum (gross) lift of the valve, based on your cam lift and rocker arm ratio. The difference between the installed height and (gross) lift indicates how much additional travel is available to the spring. For example, if the installed height of the valvespring is 2.000 inches, and the maximum lift of the valve is .5000 inch, the open spring height should be 1.500 inches.
Sufficient seat pressure is needed to keep the valves from bouncing when they return to their seats in the closed position. When valves are allowed to bounce on their seats, cylinder pressure is reduced and it can lead to tulip deformation of the valve head. If this deformation occurs, it is possible for the valve head to break off the stem.
If the engine is equipped with hydraulic lifters, the springs must exert enough pressure at the valve lifter to keep the lifter plunger centered in its travel. Otherwise, the lifter can “pump up,” causing the valve to be held slightly off its seat. This can easily be mistaken for an ignition or fuel system related misfire.
The choice of engine oil can also affect hydraulic lifter operation. If oil pressure is too high and/or the oil is too high in viscosity, this can also lead to lifter pump-up.
If you’re running aluminum cylinder heads, you must install hardened steel seats under the springs. This prevents the springs from digging into the aluminum. The steel spring seat also serves another function: to keep the spring centered and to prevent spring “walk,” which can lead to excessive valvestem side deflection. Excessive spring wander eventually wears out the guide and guide seal.
Spring seats are available in two basic styles: spring cups and spring locators. Spring cups have an OD raised lip to capture the OD of the outer spring. Spring locators have a raised shoulder at the center to register to the inner spring ID. If using spring cups, measure the diameter of the raised lip and make sure that it clears the OD of the outer spring. If using spring locators, measure the OD of the raised shoulder and measure the ID of the inner spring. In either case, you should have a fairly close (snug) fit. Consider a maximum clearance of .050 inch (for example, with a spring locator, where the inner spring’s inside diameter is .050 inch larger than the shoulder OD).
Retainers and Locks
Always check for potential interference between the retainer and valveguide, especially if you’ve moved to a high-lift camshaft. When the valve is fully opened, it’s critical that the bottom of the retainer doesn’t contact the top of the guide or guide seal. This is most easily done by installing light checking springs (to avoid unnecessarily fighting the compression force of the intended springs). During test fitting (with the cam, valves, pushrods, and rockers installed), rotate the cam and observe the clearance between the retainer and guide seal at each valve location. At maximum lift, maintain at least .050- to.060-inch clearance.
If you’re planning to use hydraulic lifters, unpressurized lifters will give you a false reading. It’s best to substitute solid lifters of the same length as your hydraulics for checking purposes. The plunger in a hydraulic lifter depresses, and this prevents you from reading the cam’s true maximum lift.
Pay attention to the design of the valve’s locking groove. Most valves have a “square cut” groove that requires locks (keepers) with square-cut keys on the ID of the locks. However, some performance valves have a bead-lock design with a radiused bead-type groove on the valvestem that requires a beadstyle lock. If you mix them up (squarecut locks on a bead-grooved valve or bead locks on a square-cut groove), the retainers pop off and you drop the valves (not a good thing).
Also, retainers and locks are machined with a specific degree matchup: the angle of the outer surface of the locks matches the inner wall of the retainer bore. These angles must match (7-degree locks with 7-degree retainers, 10-degree locks with 10-degree retainers, etc.). We can debate the advantages of different degree designs all day long but, basically, remember that you must match the assemblies.
Always buy the retainers and locks from the same manufacturer. Even though retainers and locks may be listed at 7 or 10 degrees for example, there may be slight differences in angles between manufacturers. If you buy Crane retainers, buy Crane locks. If you buy Comp Cams retainers, but Comp Cams locks, etc. Sometimes parts from different manufacturers match up, but sometimes they don’t.
Lock/retainer packages are available in three basic styles: rotating, clenching, and semi-clenching. OEMs tend to use rotating styles that allow the valves to rotate during engine operation. This ever-changing, valve clock position places the seat contact in random locations to extend the service life of the valves and seats. However, this isn’t what you want for any high-performance or racing setup, since valve rotation diminishes the optimum sealing (as set during the build).
Clenching styles lock the valve in place (via a slight interference fit), preventing rotation. Semi-clenching styles holds the valve tightly in its clock position, while allowing a small bit of rotation. For all-out racing or any high-RPM use, it’s best to lock the valve with a clenching-style lock/retainer setup.
Valve Lash Caps
Lash caps (made of hardened steel) are individual caps that are installed onto the valvestem tip. These are only required in certain applications, either for achieving desired valve lash or to protect a relatively soft valvestem tip material. Lash caps are commonly used with titanium valves (since titanium is a relatively soft material) in order to prevent the valve tips from deforming. However, some titanium valves have hardened tips (or thermally sprayed on diamond-like hardness) that eliminate the need for additional lash caps.
Lash caps are offered in various thicknesses in order to accommodate lash requirements. Lash caps should fit snugly onto the valve; loose enough to be finger installed and removed but tight enough to eliminate excessive bouncing, rotation, and relative motion. If you’re using lash caps, you must keep close watch on fit (especially for valve lash), and keep them organized with the individual valves.
Written by Mike Mavrigian and Posted with Permission of CarTechBooks