Copyright © 1996 by Quality Performance Products
DEGREEING A CAMSHAFT
A four-cycle engine’s components work together in a very precise relationship with each other. For example: crankshaft to a connecting rod; crankshaft / connecting rod to a piston; valves to a camshaft. One of the most critical relationships in an engine is the camshaft to piston / connecting rod / crankshaft timing. This instruction manual will show you how to find and adjust this relationship for the best performance results.
The tools you will need are:
1- Large degree wheel 12” to a 24" diameter (larger is more accurate)
1- Adjustable magnetic base with a 1 inch travel dial indicator .001 Division
1 - Short length of wire to bend into a pointer (Coat hanger or electric fence wire)
1 - 1/4 x 2 x 6 Aluminum plate to make a pushrod guide
The path of least resistance in degreeing a camshaft is when the crankshaft / piston assembly is able to rotate smoothly. You can accomplish this with only the # 1 cylinder piston with rings and connecting rod installed. Having the crankshaft disconnected from the transmission is helpful if performing this procedure in the chassis. Install the camshaft and the # 1 cylinder lifters into the block with light oil on the bearings, lifters and camshaft lobes. Install the cam gear(s), idler gear(s), crankshaft gear(s), etc. to line up the camshaft and crankshaft timing marks. Mount the degree wheel centered on the nose of the crankshaft so it clears all other engine components. Rotate the crankshaft until the # 1 cylinder piston is very close to TDC (Top Dead Center). Rotate the degree wheel on the crankshaft nose until the TDC marking is near the top in a position easy to read. Snug tight the bolt holding the degree wheel to the crankshaft. Bend the pointer wire and fasten it to the block. Adjust the pointer wire so it points at the TDC mark on the degree wheel. When making measurements, calculating midpoints or centerlines, always rotate the engine components in their normal direction of rotation. This will ensure that the measurements reflect what the engine components are actually doing.
To find an approximate piston TDC, set the dial indicator on top of the block so the dial indicator plunger is perpendicular to the piston top. Make sure enough dial indicator plunger travel is remaining for the piston to travel up slightly, but more importantly for the dial indicator plunger to follow the piston down approximately 1/4 inch. Using light thumb pressure on top of the piston to take up bearing clearance, rotate the crankshaft forward in normal rotation. Continue rotation until the piston reaches the end of travel at the top of the block. Set the dial indicator needle to zero. Rotate the crankshaft opposite normal rotation and then forward again to recheck your piston TDC dial indicator reading. Align the pointer so it points clearly and squarely at the degree wheel TDC mark. This is the approximate TDC setting.
To find the exact TDC location, rotate the crankshaft in reverse of normal rotation until the dial indicator drops about .200 inch of travel. Slowly and smoothly rotate the crankshaft in normal engine rotation until the dial indicator reads .100 inch of piston travel before TDC. Record the degree wheel pointer reading. Example: 15 BTDC (Before Top Dead Center)
Continue to rotate the crankshaft in normal rotation until the dial indicator reads .100 inch of piston travel after TDC (the piston came up to TDC and started back down). Record the degree wheel pointer reading. Example: 25 ATDC (After Top Dead Center)
The exact point of piston TDC will be ½ of the distance between the two recorded points. [ Example: 15 BTDC and 25 ATDC ] To find this midpoint, add the distance between 15 BTDC and 25 ATDC. The distance between 15 BTDC and TDC is 15 degrees. The distance between TDC and 25 ATDC is 25 degrees. Example: 15 + 25 = 40 This is the number of crankshaft degrees between the two recorded example points. Dividing this number by two (2) finds the midpoint. Example: 40 / 2 = 20 To locate this calculated point, rotate the crankshaft in reverse rotation past your first recorded number. [ Example: 15 BTDC ] Rotate the crankshaft in normal rotation to your first recorded point. [ Example: 15 BTDC ] Continue in normal rotation another 20 crankshaft degrees (½ of the distance between the two example points). The wire pointer will now point at 5 ATDC on the degree wheel. This is the example’s true TDC. Without rotating or moving the crankshaft, loosen up the bolt holding the degree wheel and rotate the degree wheel until the wire pointer points precisely at the TDC mark. Retighten the bolt holding the degree wheel to the crankshaft. As an option, realign the pointer to point precisely at the degree wheel TDC mark. Either method is OK; use whichever is easier. Remember to view the pointer directly in-line with the crankshaft to avoid parallax error.
Repeat the TDC operation to confirm the accuracy of your measurements. Accuracy counts, so be sure to take careful measurements and smoothly rotate the crankshaft to get exact dial indicator readings. If you overshoot your intended dial indicator reading, back up and carefully approach the numbers again. The numbers given here are only examples. Your recorded numbers will be different, but the math operations work the same way.
The next step in this process is the camshaft timing. What you want to find is the precise midpoint or centerline of the # 1 cylinder intake lobe and where this centerline is in relationship to the crankshaft and piston TDC. To do this, you need a procedure to measure camshaft lobe lift. The following pushrod guide fabrication is used primarily for inline engines, but can be used for others if the camshaft lifters are inaccessible to the dial indicator. If the lifter is accessible, the dial indicator can be setup to read directly from the lifter. You will use the aluminum stock to make a pushrod guide, if required. Measure the pushrod diameter carefully and drill a hole .005 to .010 inch larger in one end of the aluminum plate. Install a pushrod into the camshaft’s # 1 cylinder intake lifter location. Find a bolt hole in the block deck close to the pushrod and measure the distance between the pushrod and the bolt hole. It is essential that you try to place the pushrod as close as possible to the OEM location to simulate how it would actually move. Layout this measured distance on the aluminum plate from the previously drilled pushrod hole. Accurately drill a hole in the aluminum plate large enough to insert a bolt through the plate into the block deck. Bolt the aluminum plate pushrod guide plate to the block with the pushrod installed in the camshaft’s # 1 cylinder intake lifter. Make sure the pushrod is free to move up and down in the aluminum plate without binding or wobbling. Adjust the pushrod hole diameter if necessary to eliminate binding. Install the dial indicator with the indicator plunger parallel with and straight into the center of the pushrod end. Carefully align the dial indicator so the pushrod is perfectly in line and free to rotate around the dial indicator plunger. Alignment is critical to avoid cosine error.
The next step will be measuring the camshaft lobe duration at .050 inch lifter rise on the opening ramp to .050 inch of lifter rise on the closing ramp. Rotate the crankshaft assembly in normal rotation to find the camshaft base circle. The base circle is the lowest point of dial indicator travel measured from the pushrod travel. Zero the dial indicator and continue to rotate the crankshaft in normal rotation until the dial indicator reads .050 inch of lifter rise. This is the camshaft’s intake lobe opening ramp. Record the degree wheel pointer reading.
Example: 20 BTDC Monitoring the dial indicator revolution counter, continue normal crankshaft rotation until the lifter has reached maximum lift. The dial indicator will display the total camshaft lift, record this reading to compare with the camshaft specification sheet. Resume crankshaft rotation until the lifter is starting to drop. This is the camshaft’s intake lobe closing ramp. You want the camshaft closing reading at .050 inch before total lifter drop (the dial indicator will read .050 inch before zero). Record the degree wheel pointer reading.
Example: 40 ABDC (After Bottom Dead Center). The exact midpoint or centerline of the intake camshaft lobe will be ½ of the distance between the two recorded degree wheel readings. [ Example: 20 BTDC and 40 ABDC ] To find this midpoint, add the distance between 20 BTDC and 40 ABDC. The distance between 20 BTDC and TDC is 20 degrees. The distance between TDC and BDC is 180 degrees (the number of degrees in half a circle). The distance between BDC and 40 ABDC is 40 degrees. Add up all the distances in order: Example: 20 + 180 + 40 = 240 degrees. Record this reading to compare with the camshaft specification sheet. This is the number of crankshaft degrees between the two recorded example points. Dividing this number by two (2) finds the midpoint. Example: 240 / 2 = 120 degrees To locate this calculated point, rotate the crankshaft in normal rotation to your first recorded point. [ Example: 20 BTDC ] Continue in normal crankshaft rotation an additional 120 degrees (½ of the distance between the two example points). This example will give a crankshaft degree wheel pointer reading of 100 ATDC. This is the camshaft’s # 1 cylinder intake lobe centerline in relationship to the crankshaft and # 1 cylinder piston.
You may have noticed that the checking height of the camshaft at .050 lifter rise (from our example) is an industry standard for comparing camshaft specifications. The distance between your previously recorded measurements will give the camshaft lobe duration at .050 lifter rise. [ Example: 20 + 180 + 40 = 240 degrees ]
The camshaft duration numbers always refer to degrees of crankshaft rotation.
Repeat the camshaft centerline operation to confirm the accuracy of your measurements. Accuracy counts, so be sure to take careful measurements and smoothly rotate the crankshaft to get exact dial indicator readings. If you overshoot your intended dial indicator reading, back up and carefully approach the numbers again. The numbers given here are only examples. Your recorded numbers will be different, but the math operations work the same way.
You may need to correct the camshaft intake centerline from the measured point to the specification given on your camshaft information sheet. This can be accomplished by moving the camshaft with offset keys, offset bushings, or by moving a tooth on the cam gear. The procedure for calculating the camshaft timing change by moving a tooth on the camshaft gear follows:
1. Count the number of camshaft gear teeth [ Example: 60 teeth ]
2. Divide 360 (number of degrees in a circle) by the tooth count of the camshaft gear.
[ Example: 360 / 60 = 6 degrees ] The result from the division will be the number of degrees change in camshaft (not crankshaft) timing by moving one tooth on the camshaft gear. An alternative option is to use a multiple keyway crankshaft gear. Which choice works the best depends on how far the camshaft timing needs to change.
Moving the camshaft further ahead in normal camshaft rotation will advance the camshaft (smaller ATDC number) and moving the camshaft opposite normal camshaft rotation will retard the camshaft (larger ATDC number) in relationship to the crankshaft. If you move only the camshaft gear, the change to the camshaft centerline timing will be equal to 2 times the change in degrees of the camshaft gear.
Example: If you advance the camshaft gear four (4) degrees, the camshaft centerline timing will advance four (4) camshaft degrees or eight (8) crankshaft degrees. Remember the camshaft runs at ½ crankshaft speed and the timing diagrams are based on crankshaft degrees. If you move only the crankshaft gear, the change to the camshaft centerline timing will be the change in degrees of the crankshaft gear. Example: If you advance the crankshaft gear four (4) degrees, the camshaft centerline timing to the crankshaft will advance four (4) degrees.
Install the camshaft to the specifications (as close as possible) given on your camshaft information sheet. Setting the camshaft intake centerline to within one (1) degree accuracy will give the best engine performance based on the information given when ordering a camshaft. If the camshaft timing is changed, follow this guideline: advancing the camshaft centerline results in a powerband at a lower RPM, retarding the camshaft centerline results in a powerband at a higher RPM. Changing the camshaft centerline will not generally increase the width of the powerband in RPMs, but will shift the powerband up or down the RPM scale. If your application requires a different width powerband, you may need a different camshaft grind. Make sure you understand the resulting effect before making any camshaft timing changes.
The valve to piston clearance is an important issue when installing a performance camshaft. It is critical to piston and valve train life that adequate clearance is provided. A rule of thumb for valve / piston clearance is .080 inch intake and .100 inch exhaust. This should be checked by the individual assembling the engine. While the camshaft is opening the intake valve, the piston is approaching TDC (start of an intake event). The intake valve / piston clearance will typically be the smallest after piston TDC. Advancing the camshaft intake lobe centerline will open the intake valve earlier, relative to the piston position, and will advance the exhaust lobe centerline. The lobe separation (number of camshaft degrees between intake and exhaust centerlines) is a fixed parameter determined when the camshaft is manufactured. The exhaust valve is starting to close as the piston approaches TDC (end of an exhaust event). Exhaust valve/piston clearance will typically be the smallest before piston TDC.
This instruction manual is only a guideline. Its purpose is to help the installer determine the relationship between camshaft and crankshaft position. For more information on the effects of camshaft timing, valve lift and duration, lobe separation and overlap, rocker arm ratios and valve lashes, consult publications available from camshaft vendors. The installer accepts all responsibility for the camshaft installation and accuracy of degreeing the camshaft centerline to the crankshaft.
What is honing, how is it performed and why is it important? Honing is an abrasive process that improves the surface finish, size, and roundness of a bored cylinder/sleeve. The purpose is to create as close to an ideal surface as possible to mate with ring faces. Oil consumption and torque output are directly affected by the finish on the cylinder walls. Cost/benefit analysis will help determine importance.
ost has two components. Up front cost is the invoice received for the work performed. OEMs have analyzed costs associated with machining and honing a bore/sleeve in the block. The benefits of high quality standards are lower warranty cost, higher fuel economy and low oil consumption. Hidden costs are the second piece of the puzzle. A hidden cost for an OEM is customer dissatisfaction with their product for which is difficult to establish an actual dollar cost. For the performance market the up front costs are similar to the OEM’s with the additional goal of increasing horsepower. Hidden costs in the performance arena are horsepower potential never realized and horsepower produced that is consumed by parasitic losses. Detonation, windage, blowby, ring flutter, piston skirt scuffing, oil contamination and other effects will be examined. Hidden costs are real. Perspective changes perceived value.
Honing uses abrasive materials such as alumina, carborundum, silicon or diamond powder bonded to a tool that is expanded and rotated in the bored cylinder. The abrasives remove material from the cylinder as the tool is moved up and down in the cylinder. This reciprocation creates the familiar cross hatch pattern seen in cylinders. The choice of the abrasives, rpm, expansion pressure, cutting lubricant, reciprocation speed and tool type affect the process and final finish achieved. The craft of honing is in understanding the process variables, controlling them and achieving a finish compatible with the ring type and material chosen for the application. Honing is done to maximize ring seal, piston ring and cylinder wall longevity.
Piston rings seal the gap between the piston and cylinder enabling cylinder pressure to be converted into work. The sides of the ring groove in the piston and the sides of the ring seal because cylinder pressure forces them together without significant movement between those surfaces. These surfaces are very smooth and flat and when pressed together create a virtual metal to metal seal. However, the ring face and cylinder need to be sealed while the ring is moving at significant speeds. In an engine with a 5.0” stroke running 6,000 rpm, the average piston speed is 83.33 ft/second or 56.83 mph. Peak speed at mid-stroke is much, much faster. The ring must seal very high peak cylinder pressures (over 3000 PSI), maintain that seal while cylinder pressure drops as the piston moves toward bottom dead center, survive the heat of combustion (in excess of 5000 F.), withstand the surface friction of those speeds, give a low friction ride back to top dead center and then repeat. Obviously, metal to metal contact between ring face and cylinder would lead to catastrophic failure in several engine revolutions. Good rings mated to properly honed and sized cylinder walls for those type rings and engine oil create a microscopic barrier of oil captured between the ring face and the cylinder surface. That microns thick film of oil seals cylinder pressure, prevents metal to metal contact, and transfers 20% of combustion heat from piston to ring to cylinder wall and then into the cooling system. It is the barrier that separates success from disaster.
Maximum ring sealing is the goal of proper cylinder finishing and it is critical for maximum power production. Blowby is the result of deficient ring seal. Rule of thumb indicates that every 2% increase in blowby costs 1% of horsepower due to lost combustion pressure. However, lost compression is only one factor in the equation. Another factor is increased windage. Blowby creates crankcase pressure which increases windage. Imagine your crankshaft and connecting rods whipping through all the oil draining back into the pan and then add the extra combustion gases leaking past the rings. This mixture of oil and combustion gases forms a “slurry” (like whipped cream) that surrounds and rotates with the crankshaft. The parasitic loss of power due to rotating this extra mass is measurable. A reduction in oil flow (the gases entrained in the oil slurry are compressed and fed back into the oil system) and subsequent loss of lubrication and oil cooling is an additional effect of windage. A portion of the compressed air in the oil will find the path of least resistance to escape, usually in the rod and main bearing oil circuit. The loss of lubrication volume from entrained air adversely impacts valve train components as well. Once pressure leaks past a part of the top ring, a cascade of effects occurs. First the ring is distorted and contact pressure between cylinder wall and ring face oil film is increased in some areas while others areas are reduced. Second, the high speed sheet of hot combustion gases can “wipe” away the oil film below the ring causing the ring to further lose local sealing and heat transfer capability. If severe enough, combustion gases leakage can blow past the secondary and oil rings which induces piston skirt scoring. Combustion gases burning the oil film around the oil rings creates “Coking,” a carbon residue that impairs oil rings’ ability to uniformly distribute the oil film. Third, if enough ring face contact is lost the ring can flutter against the cylinder wall. The ring then loses cooling capability, becoming locally annealed (softened) allowing even more leakage and increased wear on the piston ring grooves. Leakage can travel in both directions. Combustion gases into the crankcase as previously discussed and crankcase windage pressure pushes the oil slurry up past the rings during the exhaust stroke when the piston is traveling towards Top Dead Center. Oil contamination of the combustion chamber creates localized hot spots of carbon increasing the possibility of detonation. Detonation pressure spikes are severe enough to damage rings and break ring lands on the piston. A false economy solution to blowby is to add more boost.
However, adding boost pressure compounds the problem of ring seal. Increased combustion pressures increase bore distortion, oil film contact pressures and heat transfer requirements all which lead to increased leakage. Typical boosted engines can experience leakage of over 5%. Lost pressure means lost potential horsepower. These losses quickly add up. Losing 1% of 1000 hp to increased windage is 10 HP, losing 5% to lost pressure is another 50 HP. The penalty is a diminishing return for bigger or higher efficiency turbochargers which in turn creates a larger cycle of loss. An 1/8 inch or less of ring material separates the combustion event from the oil pan. Thus ring seal is critical in capturing the increased cylinder pressure generated by improvements to camshafts, induction, combustion and exhaust systems. Unless manufacturing piston rings is a viable option, the only part of the ring seal you can affect is the cylinder wall preparation.
There are two major factors in cylinder preparation: size and surface finish. Size may sound simple but is as complicated as surface finish. Size is relative to taper and out-of-round. Taper can be categorized three different ways. Bell-mouthed taper is largest at one or both ends. Barrel is with the bore largest in the middle. Linear taper goes from the smallest to the largest, one end to the other.
Out-of round bores can be described by levels of “order.” A first order bore is round and true without any distortion. Second order distortion is oval in nature, created by poor machine accuracy or heat transfer while machining. A third order distortion is defined by a triangular shape, sometimes described as a lobe, and is caused by a combination of second and fourth order distortions. Excessive tool pressure during the boring procedure can cause lobes. High stone pressure with honing tools that are centered or supported by contact in the bore can also cause lobes. These two scenarios cause localized distortion as the cutting or honing edge pushes and moves areas in the bore with little backing or support (the middle of the sleeve or cylinder). Fourth order distortion is a square or cloverleaf shape usually created by bolt hole location and spacing.
Sizing a sleeve or cylinder has a number of issues to consider. Is the size determined by maximum or minimum measurements taken? How are these measurements taken? How cylindrical (close to absolute round and size over its entire length) is the bore? At what temperature was it measured? Distortions are difficult to accurately measure. A bore gauge located by three points and measuring across two points cannot accurately measure a second order distortion, can’t detect a third order distortion and will detect but not accurately measure a fourth order distortion. A tool rotated in the bore (dial indicator mounted on a boring bar, for example) can measure second, third and fourth order out of round. A honing tool with more edges than the order of distortion can help remove lobes left from a boring operation. A four edged honing tool removes a third order error and a five edged tool removes a fourth order error, etc. This is why super-abrasive tools have six or more cutting edges. The increase in edges allows for a decrease in individual stone pressure and better centers the tool within a distorted bore, both of which help produce a rounder finished bore.
Surface finishes are defined by Ra, Rk, Rvk, and Rvp. Very specific finishes are required for adequate oil retention and ring seal in internal combustion engines. Some definitions are needed here. All machining operations including grinding and honing leave tooling marks in the material they are cutting. Machine type, cutter geometry, machining speeds and feed rates and material type affect the finish left post machining. The average roughness of a machined surface is defined as Ra.
Ra is measured in micro inches (one micro inch is one millionth of an inch or .000001”). A profilometer is required to measure Ra. The profilometer’s diamond stylus is moved across the surface to measure distribution (size and quantity) of the peaks and valleys of the tooling marks. However, Ra does not tell the complete story of the surface profile. Other values are needed to define the surface. Rpk is the average peak height; Rvk is the average valley depth; and Rk is the average core roughness depth. All of the R numbers combined create a more comprehensive view of the surface. A graph that plots all the R values showing the extent of the load bearing surface is an “Abbott-Firestone Curve.” Plateau honing creates flattened peaks, or plateaus, which increase the load bearing surface relative to Rk and reduces Rpk (imagine the surface difference between a threaded and smooth rod.) Even more complicated, there is the concept of “lay.” Lay refers to the predominant direction in which tooling marks are found on a machined surface. However, lay does not affect R values. The cross hatch pattern typical to most honed cylinders is a type of lay.
Cross hatch is important for ring seal and ring life and the required angle is determined in part by the sleeve or block material. In cast or nodular iron cylinders a narrow cross hatch angle of less than 20 degrees will cause excessive ring rotation and resultant ring and piston ring land wear. Worn ring lands allow blowby. Conversely, too large of a cross hatch angle, or more than 40 degrees, causes a loss of oil film retention and thus sealing, and reduces ring rotation leading to increased cylinder wall wear. Nikasil and other plated bore surfaces require a flatter cross hatch of 10 to 15 degrees. Ring manufacturers publish extensive data on recommended bore finishes for their products. Following their advice is prudent unless there is sufficient evidence that another finish is better suited to the specific application.
A true first order bore at specified surface finish, correct lay and at precise size is incredibly difficult to achieve. Accurate machines with rigid spindles, correct honing tools, cutting lubricants, combined with operator skill and adequate measuring tools are all required to get close. However, despite using the best procedures and equipment, the cylinder or sleeve bore changes when the engine is assembled and then again when run under load. Head bolt loading, sleeve counterbore alignment in the top of block relative to the bottom of the block, counterbore depth uniformity and flatness, uniformity of sleeve flange height, block deck flatness and cylinder head flatness all affect cylinder bore distortion when assembled. Good block inspection and re-machining as needed, quality sleeves and proper head bolt torque procedures during assembly will help reduce distortion. Of all the possible distortions, out-of-round is more important than taper for ring seal and ring life. Better yet for sleeved blocks is honing the sleeves while installed in the user’s block and clamped in place with torque plates.
The stock block started out factory machined for accuracy, but by now can have thousands of running hours and heat cycles. This is a seasoned block. A seasoned block has moved, shifted and distorted in all areas from when factory machined. In other words, it has been stress relieved and stabilized by those thousands of hour of use. Qualifying a seasoned block, re-machining as needed, and then honing the sleeves in place will provide the most distortion free method of preparing sleeves for assembly. By installing sleeves in the block, serializing and clocking each sleeve to its position in the block and using a torque plate, the sleeve will distort as it will be in the final assembly. Honing sleeves in the block allows finish honing with minimum out of round and taper.
Good block preparation, matching ring type to sleeve finish, round and straight sleeves when installed and engine assembled, meticulous cleaning and good assembly procedures will give you the best performance for the money. The tangible benefits realized are increased horsepower, durability and consistency. Now that is the best “Bang for the Buck.”
By engineering definition, resistance against penetration. For cams and lifters, hardness is directly related to resistance against wear. A typical iron cam registers in mid- to high-40s on the Rockwell C scale (Rc). Compatible lifters register five to ten points higher. The smaller part, running hotter, must be harder to equalize wear between parts.
A number of heat-cycle processes to alter the surface hardness of a metal. The temperature of the part is raised to to the critical temperature, held there for a specified time, then allowed to cool at a specified rate to nearly room temperature. This heat cycle alters the crystal and grain structures of the metal, which affect its hardness. Some processes also diffuse carbon or nitrogen atoms into iron surfaces. All flat and roller tappets are heat treated. Some iron cams (mostly British) are heat-treated after re-grinding, to regain surface hardness. See: “CARBURIZING, CHILLED IRON LIFTER, FLAME HARDENING, HARDNESS, INDUCTION HARDENING, NITRIDING, and QUENCHING.”
Performance camshaft materials used may require carburization. 4620, 8620, P-6 ,S7 are alloys used for cams. There are others. Carburization is used for materials which have a low carbon volume. You need carbon to harden. This is a process used by all cam manufacturers. Carburization is adding carbon to all exposed surfaces to a specific depth. Camshafts I have examined are normally surfaced treated .030 /.120 deep with a surface hardness of Rockwell "C" from 55-63. Very hard for durability and to withstand the line contact of the roller. Carburizing exceeds nitriding for a performance camshaft especially for roller tappet use.
Gas nitriding is a surface heat treatment that leaves a hard case on the surface of an iron cam. The hard case is up to .010” deep and is typically twice the hardness of the core material. The process is accomplished by placing the cam into a sealed chamber filled with ammonia gas, and heating it to approximately 950 degrees F (510 degrees C). At this temperature, a chemical reaction occurs between the ammonia and iron of the cam to form ferrous nitride on the surface of the cam. As the reaction progresses, ferrous nitride diffuses into the cam core to a case depth of approximately .010”. The nitriding process is done at relatively low heat (as heat treatments go), so the core material loses no hardness. Also, the chamber temperature is raised and lowered slowly, so that the cam is not thermally shocked, which would create internal strains. Gas nitriding was originally intended for where sliding motion between two parts occurs repeatedly, so it is therefore directly applicable to solving camshaft wear problems. Ferrous nitride is a ceramic compound, which accounts for its hardness. It also has some lubricity when sliding against other parts.
Straight testing cannot be performed by Rockwell "C" because the diamond needle and weight used to protrude the needle into the surface used to check hardness would pass through the nitrided surface. One hundred fifty grams are used to measure Rockwell "C" harness. Material which has been nitrided uses a similar method to measure hardness, but uses only 15 grams; hence the name "15N" superficial hardness testing. By using this process, the actually surface hardness is measured.
A process for the surface hardening of alloy steel. Induction hardening is one of the most widely employed to improve component durability. It creates in the work-piece a tough core with tensile residual stresses and a hard surface layer with compressive stress, which have proved to be very effective in extending the component fatigue life and wear resistance. The work-pieces are heated by means of an alternating magnetic field to a temperature within or above the transformation range followed by immediate quenching. The core of the component remains unaffected by the treatment and its physical properties are those of the bar from which it was machined. The hardness of the case can be within the range 37/58 HRC. Carbon and alloy steels with an equivalent carbon content in the range 0.40/0.45% are most suitable for this process. The effectiveness of this treatment depends both on surface materials properties modification and on the introduction of residual stress. A source of high frequency electricity is used to drive a large alternating current through a coil. The passage of current through this coil generates a very intense and rapidly changing magnetic field in the space within the work coil. The work-piece to be heated is placed within this intense alternating magnetic field where eddy currents are generated within the work-piece and resistance leads to Joule heating of the metal. By quenching this heated layer in water, oil or a polymer based quench the surface layer is altered to form a martensitic structure which is harder than the base metal.
The final stage in ferrous heat-treating processes is cooling the workpiece nearly to room temperature. The rate of cooling affects the resulting microstructure in metals, and from that either hardness or toughness. Quenching cools the fastest and generates the hardest surface. The quenching liquid is often water for large parts, but must be oil for very small parts (like needle bearing rollers) to prevent them cracking from thermal shock.
A thermo-chemical surfacing process, whereby a nonmetallic, oil-absorptive coating (manganese phosphate) is applied to the outside surface of the camshaft except on the mains (journals). The lubricity of this coating permits rapid break-in of cam lobes without scuffing. (The Parker family developed this process in New Jersey in the 1920s.)
CHILLED IRON LIFTER:
A cam tappet/lifter made from high-quality iron alloy that is heat-treated during its casting. Molten iron is poured into a honeycomb mold with a chilled steel plate at the bottom, to quench and so heat-treat the face of the lifter. The heating and quench process brings carbide nodules close to the surface for excellent durability. This type of tappet is compatible only with steel and hardface overlay cams.
HARDENABLE IRON LIFTERS:
A cam follower made from a special high-quality iron alloy that is compatible with cast iron billet camshafts. The entire cylindrical body of a hardenable iron lifter is hard, in contrast to a chilled iron lifter with only its base hardened.
A small amount of spherical crown ground on the faces of most nominally “flat” tappets, to prevent the edge of the tappet from riding off the edge of a tapered cam lobe. The amount of crown is determined by the amount of lobe taper, both being set by the engine manufacturer. Normal tappet wear occurs as a “donut” partway off-centered on the face. Wear near the edge indicates a tappet with too little crown for that cam. Loss of specified tappet crown indicates a worn cam.
The small amount by which one side of a flat-tappet lobe is larger than the other, even though both follow the same profile. Cams carry taper left or taper right and zero to .003” taper, depending on the engine. The direction and amount of taper is measured best across the diameter of the base circle. Hold the front of the cam to your left (as a cam-grinding machine does). If the forward (left) side of the lobe is larger, that is taper-left (TL). If the rearward (right) side of the lobe is larger, that is taper-right (TR). All lobes should measure with the same amount of taper, but not necessarily the same direction. TR pushes cams into the block, off the angled pressure from tappets. Engines with TL, mixed tapers, or roller tappets (with no taper) require a cam thrust plate. Lobe taper works with tappet crown and tappet bores offset from lobes bores to drive flat tappets into rotation. See: “Tappet Crown, Tappet Rotation.”
Flat tappets must rotate in their bores, to continually present a fresh part of their face against a rotating cam, and thus equalize and minimize wear. In contrast, roller tappet bodies must NOT rotate at all. If the roller tappet body is allow to rotate, the roller wheel edge will impact the camlobe. The can result in catastrophic damage to the engine. Rotation is driven by offsetting the lifter bore from the center of the lobe face, lobe taper in the same direction as lifter offset, and lifter crown to match lobe taper. Before installing tappets, check that each lifter is free to rotate in its bore, and apply only engine oil (not sticky “cam lube’) on the sides of lifters. If a flat tappet does not rotate sufficiently, or at all, that lifter and cam lobe will wear out prematurely, perhaps as soon as break-in.
A man-made motor oil additive essential for dry lubrication between camshafts and flat tappets, where extreme pressure squeezes away all the oil molecules. ZDDP* circulates with oil in 800-1200 parts-per-million, until it is crushed within a cam-lifter interface and plates itself into the iron surfaces. Progressive reduction in percentages of ZDDP in motor oil since 2001 is causing premature wear in many high-performance street cams. (*Zinc dialkyl dithiophosphate.)