Mopar DiY

Mopar Engine Performance Guide: Camshaft, Lifters and Cam Drive

by

Selecting a camshaft is one of the most important decisions you make when building a max-performance engine because the cam controls crucial timing events. And those events need to occur at the proper time in the engine’s cycle and in conjunction with the engine’s other component operations. If these events do not occur at the correct time, the engine does not reach its performance potential.
 

This Tech Tip is From the Full Book, HOW TO BUILD SUPERCHARGED & TURBOCHARGED SMALL-BLOCK FORDS. For a comprehensive guide on this entire subject you can visit this link:
LEARN MORE ABOUT THIS BOOK HERE

 

SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://mopardiy.com/mopar-engine-performance-guide-camshaft-lifters-and-cam-drive/

 
Once you decide to change the cam, you are faced with a vast selection of manufacturers, profiles, designs, and options. The cam dictates most of the valvetrain specs and should work with the amount of air that the cylinder head can flow and with the intake manifold/induction system. The camshaft is part of the engine’s short block, so cranks, pistons, rods, and valvetrain need to be considered.

On the other hand, cylinder heads are very popular. With the Magnum versions, installing a cam and tappets should be done before the heads are installed because after the heads are installed, it is very difficult to install the tall, hydraulic tappets under the edge of the head.

Production Cams

Of the major parts within the short block, the camshaft is substantially different between A-engines and Magnum engines. The A-engine has a long nose at the front of the cam; the Magnum engine has a short nose. This difference is because the A-engine has a mechanical fuel pump eccentric-mounted on the nose and the Magnum engine does not use a mechanical fuel pump.

A few Mopar Performance crate engines, however, were based on the Magnum engine, and they were designed for use with a cam that had a long nose and a mechanical fuel pump.

A-engine and Magnum cams look similar because the difference in overall length is only about 1/4 inch. The distributor drive gear is located at the rear of the cam along with a small number-5 bearing journal. The other four journals are basically the same size (just under 2 inches). Cams are made of cast iron or steel. Most aftermarket cams are stamped with profile numbers or manufacturer numbers, but production cams have no actual stamped or cast numbers.

Production cams were mechanical (1964–1967), hydraulic (1967– 1985 and 1991), and hydraulic roller (1992–2003). It is not easy to differentiate them.

If you have a small-block cam but don’t know which one, you use cam lift to help identify it. (Measure lift at the tappet, if possible, and multiply by 1.5 to use the chart on page 52.)

Cam selection is crucial for any engine build, and correct cam selection is critical for a max-performance engine because these timing events largely dictate the performance potential. Most cams look alike; it is very difficult to tell a hydraulic from a mechanical cam and even a hydraulic roller doesn’t stand out. The exception is the mechanical roller because the lobes are so large; the high lift and long duration make the lobes almost look square.
Cams are often sold as cam kits that include the tappets. The hydraulic roller tappet can give you clues about the cam because the mechanical roller tappet looks different. (See the hydraulic roller chart in Chapter 4.) There are three levels and two specific cams per level (listed by profile number). You can’t get any more specific than that.
The main function of the camshaft is to open the valves. The tappet is the first part that helps transfer the cam movement toward the valves; the pushrods are the next part in the valvetrain. This chapter covers the cam and tappets; the pushrods are covered with the rest of the valvetrain in Chapter 7.
Common
A mechanical cam requires adjustable rocker arms. The hydraulic cam does not require adjustable rockers. The stamped rockers shown can only be used with hydraulic cams. What isn’t as easily seen is that the A-engine oils the valvetrain up through the block and heads to the rocker shaft (shown), which distributes it to the rockers and valves. These stamped rockers are used on most 318s, 340s, and 360s but not on the 273 or the 340 T/A.

If you have tappets that operate with the cam, identifying your cam style is easier.

The lift number can also help identify aftermarket profiles if no stamped identification numbers are visible.

Aftermarket Cams

Comp, Crane, Isky, Bullet, Edelbrock, and other cam manufacturers offer a wide range of profiles for flat tappets, hydraulic rollers, mechanical rollers, etc. Assuming that the cylinder head is matched to the cam, the more valve lift you put in, the more power the engine makes. However, remember that higher lifts create longer durations, and long durations can cause serious problems with street engines and drivability.

As the valve lift increases, you need to select the appropriate cam. A base performance cam is hydraulic, and then you move to hydraulic roller cams, to mechanical cams, and to mechanical roller cams. Billet cams tend to focus on the racing end of the cam scale.

Camshaft Technology

All small-blocks are four-stroke engines, which have four phases to the engine cycle: intake, compression, power, and exhaust. Each phase is 180 crankshaft degrees. This means that the full engine cycle takes two full revolutions of the crank (360 degrees makes one complete revolution). Because the cycle takes two revolutions, the camshaft runs at half-crank speed and the cam sprocket is twice as large as the crank sprocket.

Match the cam’s lift and duration to combustion chamber capacity, head port size, exhaust system design, and other aspects of the engine. There are many more aspects to the cam than lift and duration, but these two are important. Remember that the nose of the cam or max lobe lift must fit through the cam bearing’s inside diameter. This means that in a given engine, if you want a cam with more lift, the manufacturer must grind down the base circle to gain lift or lobe lift.

Lift

The cam lift, or lobe lift, is the distance that the tappet moves upward in the tappet bore. However, it is more common to discuss valve lift, which is the distance that the valve moves off the valveseat. These two types of lift are influenced by the rocker arm ratio (typically 1.5 or 1.6). Valve lift tends to be the most popular lift number, and it is also the easiest to measure directly.

Duration

Duration is defined as the number of crank degrees that the intake and exhaust valves are open off their seat. Advertised duration is the most popular and probably the most common. It is loosely defined as the point at which the tappet is approximately .012 to .017 inch off the seat (zero position), but some aftermarket companies use a tighter tolerance, maybe .005 inch.

The second type of duration is called “duration at fifty,” or “duration at .050 inch.” With this duration, the tappet is .050 inch off its zero position. The duration at .050 is always smaller than the advertised duration, but it’s much more useful in all-out race cams and engines.

Events

The engine cycle includes four cam events: intake opens, intake closes, exhaust opens, and exhaust closes. These four events are measured in degrees relative to TDC or BDC. The cam’s duration can be calculated if you know the event measurements.

Overlap

A cam’s overlap is the amount of time that both the intake and exhaust valves are open. It is defi ned as the sum of the intake opens event (before TDC) and the exhaust closes event (after TDC). Street cams have low overlaps and race cams have high overlaps.

Centerline

After a manufacturer grinds a cam, there is only one specifi cation that you can change, the installed cam centerline. This is the relationship of the cam to the crankshaft, sometimes called the intake centerline.

The manufacturer grinds the cam centerline (or lobe centers; see sidebar “Camshaft Terms”) into the cam, and after it’s ground, you can’t change it. You can, however, adjust cam advance or retard.

For example, a 340 may be ground on 114-degree centers and installed at 114 degrees intake. By definition, the exhaust is also at 114 degrees. So, if you install this cam 5-degrees advanced, the intake becomes 109 degrees and the exhaust becomes 119 degrees.

Geometry

Valvetrain geometry starts with the camshaft location and the tappet angle (all production small-blocks use a 59-degree tappet angle). This geometry is suitable for many high-performance street applications, but as you get into all-out racing cylinder heads and racing valvetrains, improvements can be made.

Most valvetrain issues become apparent at high RPM, and that’s usually more than 7,500 rpm.  If your engine generally runs more RPM and makes more horsepower, the fi rst major improvement is changing the tappet angle.

Geometry is an overused term in cams and valvetrain discussions. For the rocker arm, it relates to the center of the rocker arm tip being centered over the valvestem. A Magnum valvetrain is shown.
The pushrod angles to the tappet must be within spec. In this view, the tappet and the pushrod are almost in a straight line. You really want more intake airflow, so you may need to move the pushrod over and use offset rocker arms. The trick is the side view (looking at the pushrod to tappet angle from the front of the engine/head). These are 59-degree tappets and the straight line occurs with 48-degree tappets.
The A-engine front cover is unique (hole in the side). MPI fuel injection can be installed on the A-engine by removing the eccentric and placing a fuel pump block-off plate over the hole in the front cover. The Magnum cover (shown) has no mechanical fuel pump boss. If you want to add the mechanical fuel pump capability to a Magnum engine, you should change both the camshafts (use A-engine style) and the A-engine front cover plus the A-engine water pump. I recommend using the March serpentine front-drive conversion, so you don’t end up running the water pump backward.

With the cam installed, the thrust plate bolts to the two bolt holes above the cam and the one bolt below and at the left of the cam.

 



 
If you draw a straight line from the race rocker arm pivot in the typical race cylinder head to the center of the camshaft, the tappet angle is 48 degrees. It is very diffi cult and very expensive to change to this angle on an existing block. Knowing this, Mopar Performance added material to its race blocks to allow for a 48-degree tappet. The casting is designed to allow machining of the race blocks with either-style tappet. If you have a race block machined for 48-degree tappets, you must use camshafts that are ground for 48-degree tappets.

Cam Oiling

All cams are oiled from the main bearings. Magnum engines oil the rest of the valvetrain through the pushrods from the tappets.

All A-engines oil the heads and valve gear through the block and head (machined passages). This oiling path starts at the number-2 and -4 cam journals (the cam has five). It is a good idea to be sure that any cam that you use has the number-2 and -4 cam journals drilled through and grooved to help move oil to the cylinder heads and upper valvetrain at all engine speeds.

Cam Gear

Magnum engines use a forged steel cam and special hardened oil pump drive gear that mates to it.

These look similar to the standard A-engine gear/drive, but they should not be switched. You cannot use a standard A-engine intermediate shaft and gear on Magnum cams.

If you want to use steel cams (and, until recently, race mechanical rollers) in an A-engine, you have to change the gear to an aluminum-bronze gear. It is gold colored, which is very obvious. This aluminum-bronze gear or shaft assembly is available from Crane or Comp Cams. It also works with Magnum cams.

High-Performance  and Race Cams

These are considered to be any cam that is larger than stock or is a service replacement. They are typically made by the aftermarket or Mopar Performance. You should always replace the tappets when you replace the camshaft.

Big Hydraulic The 340 cam is the largest of the production designs, so these cams start in the .450-inch lift area and go up. Big hydraulic cams may have .480- to .520-inch lift. The advertised durations tend to be in the 280- to 290-degree area.

Hydraulic Roller The hydraulic roller cam is standard in all 5.2L and 5.9L Magnum engines. The Magnum roller cam is shorter than the typical A-engine cam because the fuel pump eccentric was removed from the front of the Magnum cams.

The tappet location spider and figure-eight (dog bone) hardware does not fit the typical A-engine block. The exception is the 1988 to 1991–1992  A-engines, which had hydraulic roller cams also. To convert an A-engine to a hydraulic roller cam, use the Comp Cams or Crane conversion kit, cam, and tappets. To install bigger hydraulic roller cams in the Magnum, install better valvesprings.

The 1986–1991 318 and the 1987–1992 360 cams are at the end of the LA-engine’s long production run and they were switched to hydraulic roller cams before the basic engine conversion to the Magnum family. This makes them unique in the LA family. Crane offers cams for these engines. The 1985 and earlier cams do not work in these engines.

Mechanical Select a mechanical cam when your engine needs a cam that’s bigger than the .520-inch-lift hydraulic cam. Mechanical cams with .500-inch-lift area were produced, but lifts of .550 to .600 inch are more common.

In addition, you must install adjustable rocker arms when a mechanical cam is added. The exception is the 340 6-barrel engines, which already have adjustable rockers. Mechanical cams may also require an upgrade in valvesprings, such as a dual spring.

Mechanical Roller For the past 20 years, Pro racing classes and similar engines have used mechanical roller cams. They allow more lift without breakage than the standard mechanical. For many years, mechanical roller cams peaked at about .700- to .750-inch lift. If the cylinder heads were limited (such as stock castings that were ported or heads limited by their valve size), around .650-inch lift was more likely.

Then, better and bigger cylinder heads were introduced, and mechanical rollers grew even bigger and the valvesprings became stronger. The upper limits are still open, but valvespring loads are more than 750 pounds and valve lifts are approaching 1.00 inch. Part of the technology that allows these very large changes is the big 60-mm roller cam bearings.

Three bolts hold the plate and the small bracket in place. The small bracket has an index tab that locates it properly; it fits into the fourth hole in the plate.
Magnum engines already have a hydraulic roller cam and the hardware to allow its use. The A-engine does not have this hardware and swapping the Magnum hardware to the A-engine is not recommended. To install hydraulic roller cams in the A-engine, use a complete conversion kit from a cam manufacturer, such as Comp Cams or Crane. The major difference between the Magnum roller hardware and the aftermarket is how the guide bar systems work on the two tappets. The guide bar must keep the tappet squared to the cam lobe or the cam lobe and tappet will both fail.

Roller Cam Bearings The 50- and 60-mm roller cam bearings require their bearing bore diameter in the block to be larger; it must be much larger in the 60-mm version. Cam bearing bore cannot be increased on stock production blocks because the bulkhead does not have enough material to bore. Mopar Performance race blocks, called R3s, have material added and allow for this modification.

Cam Selection Process

Selecting the correct cam for an engine combination is dependent on a wide range of factors, so you should take a methodical and detailed approach when determining the specific cam for your engine. Be sure your cam works in conjunction with and complements the entire engine package, including heads, intake, carb, and exhaust.

If you put all that stuff into a chart, it would be so complicated that no one would ever figure it out. Instead, I have included my recommendations in two charts for each cam, the second one shows some of the engine hardware that will work.

Cam Installation

Properly orienting the cam with the crankshaft requires some detail work so the engine performs well. The factory method of lining up the dots on the crank and cam sprockets is a starting point, but if you bought a new cam, follow the manufacturer’s recommendations. Often, an aftermarket cam must be installed in a different location. To fi nd this installation location, you need a degree wheel and a dial indicator.

Using a Degree Wheel

As I recall, high school geometry says that a circle is divided into 360 degrees. Engine builders use a degree wheel to install and centerline camshafts and to check camshaft locations relative to the crank.

My recommendation is to use the 0-180-0 version (available from Mopar Performance) because I prefer to think of the relationship of the crank to the camshaft in terms of the cam centerline, which is one number that defines one engine aspect.

The other version (0-90-0-90-0 style) is designed mainly to work with the four-event installation method, which has degrees for the four events: intake opens (IO), intake closes (IC), exhaust opens (EO), and exhaust closes (EC). You also have to consider the locations before or after TDC and BDC.

Adjusting the Centerline

After you have determined the cam’s actual centerline, slip the cam sprocket off the nose of the cam and remove the stock key. Install the new offset key and slip the sprocket back into position. It is easier to adjust the centerline using the dial indicator than it is to calculate which direction it goes, offset to the left or offset to the right. If you guess wrong and the offset is installed incorrectly, the dial indicator and degree wheel tell you.

Aligning Timing Marks

Each tooth in the cam sprocket is about 7.5 degrees wide; aligning the dots is only accurate to 7.5 degrees. The installed centerline could be 107 or 123, which is one tooth off in each direction. Therefore, if you want to install the cam at 112 or 118, you can’t get there with the lining-up-the-dots method. However, actually doing the lining-up-the-dots as the first step saves you a lot of time in the long run. It also catches a one-tooth-off error.

There are two styles of degree wheels: the 0-90-0-90-0 layout and the 0-180-0 layout (shown). I recommend this version because it is much easier to focus on one number, the centerline. You will make fewer mistakes.

Cam Degreeing

Degreeing the cam (centerline installation method) requires a degree wheel. Always remember that the cam needs to have a specific relationship with the number-1 piston. So the zeroing process, which is the first step, is extremely important.

Advancing/Retarding

When degreeing a cam, the cam movement (changing the centerline) is called advancing or retarding the cam. If you start with a 115-degree centerline, and you move the centerline toward 100 degrees, you are advancing the cam. If you move the centerline away from 100 degrees, you are retarding the cam.

Most degree wheels read 0-90-0 so that a cam centerline of 115 degrees will actually read as 65 degrees on the degree wheel. You can subtract the actual reading (65) from 180 degrees for the actual cam centerline (115). The 0-180–degree wheel reads 115 degrees directly; no calculations required.
With the cam installed in the block, the next step is to line up the dots on the crank and cam sprockets and install onto the cam and crank. Get the number-1 piston to TDC and line up the dots so they are opposite each other. Then rotate the cam so that the keyway in the sprocket lines up with the key in the cam. Slip the timing chain over the crank sprocket and slide the cam sprocket over the nose of the camshaft. Slip the cam sprocket into place and check to see if the dots line up.
Lining up the dots on the crank and cam sprockets is the first step in installing the cam correctly. It will save time and effort in the long run. You can fine-tune this process by using the steel scale to line up the dots with the centers of the crank and cam sprocket.
Next, the degree wheel is attached to the nose of the crank with the dampener bolt and a large washer (use extra washers as necessary). Use a piece of bent wire as a pointer; select two front cover bolt holes to which you’ll attach the pointer. Place the dial indicator on the top of the number-1 piston and rotate the piston to TDC and zero the indicator. Rotate the piston so that the indicator now reads .050 inch and read the pointer, which indicates 20 degrees. Reverse the direction of rotation and bring the piston up to .050 inch below TDC and read pointer again; it should indicate 30 degrees. If the pointer was properly zeroed, it will read the same at both locations. Because there is a 10-degree difference, bend the pointer 5 degrees toward zero. Repeat procedure and both readings should now be 25 degrees.
Install the tappets into the tappet bores for the number-1 cylinder. Lube with very thin oil. Reposition the dial indicator to the top of the intake tappet (outside edge, flat surface). Rotate the crank one full revolution and return to TDC with both tappets on the base circle. Carefully rotate the crank in the clockwise direction until the intake tappet reaches max lift; zero the indicator. Rotate the crank clockwise until the tappet reaches the base circle and starts to lift again. Stop at the point .050 inch below max lift point and read the degree wheel; it should be 85 degrees. Continue rotating clockwise through max lift and back to the .050-inch down point and stop to take the second reading. It should be 145 degrees. The centerline is halfway between these two points, at 115 degrees. If you wanted the cam installed at 115, you are finished. If it measures 107 degrees, then you are a tooth off on the sprockets or the dots are out of line by one tooth. If you want to install the cam at a point between these two numbers, you will have to use offset cam keys or multi-key sprockets.

Tappets

A tappet is about 1 inch in diameter and 2 to 3 inches long. The face of the tappet rides directly on the lobe of the cam. Therefore, the tappets must be the same as the cam design, that is, hydraulic to hydraulic, mechanical to mechanical, etc.

The most common mode of tappet failure is scuffing. Always replace the tappets when you replace the cam and keep the tappets matched to the lobenumber-1 intake tappet on the number-1 intake lobe.

Cam Drive

You should always replace all three pieces of the cam drive if it appears to be showing too much wear. You should replace the cam drive on high-mileage engines.

Belt, gear, silent, and roller are the four cam drive types. The belt drive is made by Jesel and should be considered a drag racing part. Several companies make gear drives but I recommend Milodon because it fits under the stock front cover (most gear drives replace the stock front cover). The silent chain is the typical production version and should be replaced for any performance application.

Crane, Comp Cams, Milodon, and Cloyes make roller or double-roller timing chains. Cloyes has several versions of the roller-chain cam drive with three or nine keyways for cam alignment, along with standard and billet gears.

Cloyes offers a hex-adjust option for the Mopar big-block but not the small-block yet, maybe soon. Any of the roller assemblies are fine for the street, but the special tensioner offered by Mopar Performance (Mancini Racing in Detroit) is a nice trick for the street: durability and accuracy over time.

The valve-to-piston clearance is an important clearance; with bigger cams, valve notches are typically cut into the top of the piston. As a general statement, advancing the cam (moving centerline from 115 to 105 degrees) will hurt valve-to-piston clearance, while retarding the cam tends to help the valve-to-piston clearance. You generally want to measure the piston’s valve-to-piston clearance early with the cam properly centerlined (and adjust the valve notch size) to avoid future problems.
This is the most common tappet used in production and also for street/strip. It adjusts automatically for wear and removes any lash that is in the system. Typically, this type of tappet is used with a stamped rocker arm that requires no adjustment. The 1970 340 6-barrel engine used a hydraulic cam with adjustable rocker arms. If you are going to use a hydraulic cam with adjustable rocker arms, adjust the rocker to zero lash as you would for a mechanical cam and then turn the adjusting screw down one more full turn. Note the oil feed hole in the side two-thirds up from the bottom.
The hydraulic tappet is quite complicated inside and it is designed to adjust about .100 inch up and .100 inch down. You do not want to get too close to either end of the adjustment range. The insides of the standard hydraulic tappet and the hydraulic roller tappet are very similar. The primary parts are the main tappet body, the small spring, the plunger, the plunger cap, and the retainer clip.
The Magnum hydraulic roller tappet adjusts for wear and lash automatically. The mechanical roller or race setup uses a guide bar to keep the roller square to the cam lobe as the cam rotates, and it usually attaches to the tappet body by a slot, pin, or button. The Magnum’s production location system has a yoke that slips over the outside of the tappet body, which is square on the top. The yoke acts like a guide bar and keeps the tappet from turning in the tappet bore. A spider bracket holds the eight yokes (one per cylinder) in place; three bolts attach it to the center of the tappet chamber.
Magnum blocks have three machined bosses in the tappet chamber to accept the spider’s attaching bolts. These bosses are not in an A-engine block, so it is difficult to add the spider to the earlier engines. In addition, the top of the tappet bore is not machined to accept the yoke. The aftermarket hydraulic roller cam conversion kits for the A-engine use a hydraulic roller tappet that uses a guide bar to control rotation rather than the yoke. These aftermarket kits allow you to convert the A-engine to the hydraulic roller cams.
The hydraulic roller tappet should be installed with the oil hole in the side of the tappet body pointing toward the center of the engine, away from the tappet wall. In the tappet on the right, the oil hole is just above the top of the tappet base and pointing away from the block.

These mechanical roller tappets have been around racing for over 40 years and now, after a slow start, almost all race cams are based on the mechanical roller cam. The mechanical roller uses a guide bar, typically attached to the tappet body, which means that these tappets are installed in sets of two.

 



 
Cloyes makes a multi-keyed sprocket, which is a version of the roller chain. The difference is in the two sprockets because they have more than one keyway for installation. And it doesn’t require offset keys to centerline the cam. There are often three keyways but there can be as many as five. Each keyway has a unique dot for alignment.

Timing Sets

Magnum engines use special hardened gear on the intermediate shaft. Production A-engines use a cast-iron gear. With any steel cam (typically a roller), an aluminum-bronze gear (brass/gold in color) must be used.

The silent chain is the standard cam drive in production, but you always upgrade to a roller chain for performance applications. The silent chain crank sprocket has the wide teeth rather than the sharp, bicycle teeth used on the roller chain.
Gear

 

The roller chain or double- roller chain looks like a bicycle chain with two rows of links rather than a single row. This is the standard performance setup. Note that the crank sprocket has more than one keyway in it.
The belt drive system is the newest cam drive setup and seems best suited to drag racing. Basically, it replaces the chain with a cog belt and the toothed sprockets with cog pulleys.
The hydraulic pushrods can be installed in either direction but the mechanical pushrod must be installed with the rocker arm cup up (shown at right), toward the cylinder head. The rounded pivot goes into the top of the tappet. It works like a little ball and socket joint.
Gear drives are used for racing. The most popular style of gear drive has two small gears mounted to a crossbar that holds them in place between the crank and cam sprocket.

 

Oil Pump Drive

Max-performance applications require the use of a hardened oil pump shaft and an upgraded oil pump gear. A high-volume pump places a higher load on the oil pump shaft, so it needs a hardened tip. Mopar performance offers upgraded pump driveshafts and distributor gears.

The camshaft drives the oil pump and the distributor off the gear at the rear of the cam. The gear actually drives an intermediate shaft. For max performance it is a good idea to upgrade this shaft to a race unit. The one tricky part is roller cams. All mechanical roller cams are steel; the Magnum’s hydraulic roller cam is a steel alloy.
The Magnum engine uses a special hardened gear on the intermediate shaft. The A-engines use the aluminum-bronze gear, which looks like brass with any steel cam

 

Written by Larry Shepard and Posted with Permission of CarTechBooks

 

GET A DEAL ON THIS BOOK!

If you liked this article you will LOVE the full book. Click the button below and we will send you an exclusive deal on this book.

Reader Interactions