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What is meant by Degreeing the Camshaft, and why is it necessary?
The phrase "Degreeing the Cam" means you are making sure the camshaft's position in the engine coincides with that of the crankshaft, so that their rotations are synchronized. This is the only way you will know if the rise and fall of the pistons properly matches the opening and closing of the valves, so the engine runs efficiently. A few degrees of misalignment (advanced or retarded) can affect the engine's operation dramatically.
If the circumstances were perfect, one would only need to line up the marks on the timing chain sprockets and the cam would be degree'd. In reality, you are dealing with a group of components (the camshaft, crankshaft, timing chain, and sprockets), all with their own standards and tolerances. If these tolerances are off, they can stack up against you and throw your motor out of synchronization. Without degreeing the cam, you can never be sure if all the parts are in correct position at the precise time they are suppose to be. As such, we always recommend that you "degree the camshaft" whenever possible, even if you have to rent or borrow the tools. Be sure to read our tech article on Camshaft Installation Tips.
ALWAYS DEGREE THE CAMSHAFT - DON'T RELY ON THE DOTS |
There are two ways to degree a cam, so which is better?
Currently there are two popular methods for degreeing a cam: the centerline method, and the duration at .050" method. We believe it is far better to degree the camshaft with either method, than not to degree the cam at all. While the duration at .050" method is more accurate, the centerline method is easier and has less chance for errors. For your average street application, the centerline method is adequate, while the duration @.050" method is preferred if you are building for maximum horsepower.
The main problem with the centerline method is it has you finding the theoretical centerline of the intake and/or exhaust lobe and lining up on it. It makes the basic assumption that the cam lobes are symmetrical, with the opening side of the lobe being the exact same shape and size as the closing side. The truth is that most lobes are asymmetrical, with the opening side of the lobe being much more aggressive and the closing side more gentle.
Therefore, when you attempt to locate the centerline of an asymmetrical lobe, there is an automatic error factor which could be off 2 degrees or more. Since the duration at .050" lift method is not affected by the asymmetrical lobe design, it is more accurate and the best way to degree the cam if you are seeking every ounce of power you can get from your motor.
A simple explanation, using the Centerline method.
A camshaft is ground with a predetermined distance between the intake and exhaust lobes. This distance is determined by the cam designer and is known as the camshaft's "lobe center", which is usually between 104-114 degrees. This would be 208-228 degrees at the crank, since the crankshaft turns twice for every revolution of the camshaft. Using the centerline method, readings are taken at a predetermined distance before and after top dead center. These readings are then split, giving you the camshafts centerline. The cam is then adjusted so that the centerline is an equal distance between these two points on the degree wheel. However if it is desirable to advance the camshaft one would merely move the centerline of the intake lobe closer to T.D.C. This is explained in greater detail below.
A simple explanation, using the Duration at .050 method.
Using the Duration at .050 method, you start on the base circle of the lobe where there is no lift. Then by rotating the engine you move up the opening side, go over the top of the lobe, then move down the closing side, finishing back on the base circle.
The dial indicator will move from zero, up to maximum lobe lift, then back to zero during this revolution. When rotating the crankshaft you stop at two key points and take readings from the degree wheel. Both readings are taken when the dial indicator shows .050" of lifter rise, which occur on the opening side and again on the closing side of the lobe. These readings are then compared to the specifications on the cam card to see how closely the cam is installed to the proper alignment. If necessary, corrections can be made to put the camshaft in the exact position that is intended by the cam manufacturer.
Correcting or adjusting the cams location.
There are several methods you can use to adjust the location of the camshaft to correct for misalignment. Most high performance timing chain sets have the lower crank sprocket machined with three or more keyways, allowing you to advance or retard the camshaft. There are also offset keys made for the crankshaft. Another popular method is offset eccentric timing bushings that can be installed in the upper camshaft sprocket to change the camshaft's position in relation to the sprocket, however this is only on camshafts that use a dowel pin for indexing. Use any of these methods to correct the position of the cam, then degree the camshaft once more, to be sure it is correct.
Important tips to remember when "Degreeing a Cam".
Clean off any excessive lubricant from the lobes and lifters that you are checking. Thick oil, especially assembly lube (paste) can cause false readings to occur. Wipe the parts clean before checking, and remember to re-lubricate them when you are finished.
If you make a mistake and rotate the engine past the point you wished to take a reading, do not back up the rotation. If you do, any slack in the timing chain or lash in the gears will affect the readings, causing an error. If you miss your stopping point, just continue rotating the engine in the normal direction until you return to the desired point.
Make sure the angle of the dial indicator plunger is at the same angle as, or parallel to, the valve stem. You want to read "straight line" (linear) movement of these parts, so the plunger must be properly aligned.
What tools are need to Degree the Cam?
Beyond your normal everyday hand tools, you'll need a few special tools, as follows:
1. A degree wheel, a professional fully degreed damper, or a piece of degree tape which is installed on your stock damper. Be sure to get the tape that matches the diameter of the damper. Whatever you use, just make sure it gives you accurate markings for 360 degrees.
2. A stable pointer that can be mounted to the engine, so that it points to the degree wheel or balancer markings.
3. A dial indicator with at least a half inch of travel in .001" increments, with a rigid stand that attaches to the engine, preferably with a magnetic base or bolts.
4. A positive piston stop, which can be used to locate T.D.C. (top dead center). You can make your own by using an old spark plug. Simply remove the porcelain insides, then drill and tap the interior of the spark plug housing and thread a long bolt through it.
5. At least one solid lifter (preferably two). If you have non-adjustable rockers, you'll also need at least one adjustable pushrod (preferably two). You can get by with one of each, but it's nice to have two, one for the intake and for the exhaust.
All of the above tools, with the exception of an adjustable pushrod, are in our Cam Degree Kits. We also offer a Cam Degree Video, which explains both methods and walks you thru the process, step by step. Be sure to read our tech article on Camshaft Installation Tips.
Before you begin the set-up procedure, install the camshaft and timing chain set with the dots lined up as you normally would. Be sure to read our Camshaft Installation Tips. Install solid lifters, and pushrods, for both the intake and exhaust valves in the number one cylinder only. It is not necessary to install the rest of the lifters or pushrods. If you have non-adjustable rocker arms, use an adjustable pushrod. Once the rocker arms are installed, set the valve lash to zero, leaving the pushrods loose enough so that you can easily spin them with your fingertips. DO NOT preload the lifters. Rotate the crankshaft, so that both the intake and exhaust valve are closed and the piston is at the top of the stroke (approximately at top dead center). This can be a rough guess, but it may save you from making a mistake later on.
The first step, using either method, is to install a degree wheel, a pointer, and a positive piston stop, which is used to locate Top Dead Center (TDC). First, attach the degree wheel to the balancer, making sure you can rotate the crankshaft once it is installed. Next, mount the pointer securely on the engine block, adjusting it so that it points to the zero on the degree wheel. A steel coat hanger works nicely, as it can be easily bent to any shape. The last step is to install the piston stop in the number one cylinder. Start by turning the crankshaft in the opposite direction (counter-clockwise)15-20 degrees, then turn the piston stop in until it touches the top of the piston. This will ensure the piston stops before reaching TDC. Then back it off the stop another 10-15 degrees.
Determining Top Dead Center (TDC)
Begin by rotating the crankshaft by hand in a clockwise direction, until the piston comes up and stops against the piston stop. DO NOT use the starter or you may damage the piston. Look at the degree wheel and write down the number of degrees shown by the pointer. Next hand turn the engine in the opposite direction until the piston comes up and once again stops. Look at the degree wheel once more and write down the degrees it now reads. Add this reading to the first reading and divide the answer by two. By splitting the difference, the resulting answer will give you the point of TDC. Move the pointer so that it points to that number. Next loosen the degree wheel and turn it until the pointer indicates zero, then re-tighten the bolts. Make certain you do not disturb the position of the crankshaft or the pointer when you are turning the degree wheel.
Rotate the engine again, first in one direction, then in the other direction, making note of the readings when the piston stops in both directions. If both readings, on each side of zero (TDC), are an equal distance (in degrees) away from the zero, the degree wheel is properly adjusted and the zero mark now represents true TDC. At this point the piston stop can be remove, however if you are unsure or have any doubts, repeat the process. Locating TDC is CRITICAL if you are to Degree the Cam successfully.
Finding TDC on your harmonic balancer.
Even without a degree wheel, you can and should calibrate TDC on your harmonic balancer when building or assembling a new engine. By using the steps above you can scribe a mark on the harmonic balancer. Each time you contact the positive stop, rotating both forward and backward, scribe a mark inline with the factory pointer on the timing cover. TDC will be exactly between the two scribed stop marks. Carefully calculate and scribe a permanent TDC marker between these two stop marks. This can be very useful later on, as TDC is the point from which all ignition and valve timing is based.
Setting the Dial Indicator.
The next step is to install the dial indicator. While we recommend setting the dial indicator so that the readings are taken off the valve retainer, there is some controversy in this method. Many cam manufacturers recommend taking the reading from the top of the lifter, however this is a bit impractical for our inline sixes as the lifters sit deep in the lifter galley. On the other hand, some cam manufactures recommend using the valve retainer for taking readings, since it compensates for pushrod and rocker arm deflection, reduces errors, and is easier to set up.
The dial indicator and stand must be attached securely to the engine, as any deflection will cause an error in your readings. It is very important to make sure that the angle of the dial indicator plunger is the same angle (parallel) to the valve stem. With the dial indicator in position, hand rotate the engine in a clockwise direction (when standing in front of the engine) until the intake valve is fully closed, then set the dial indicator to zero. The lifter is now on the base circle of the cam lobe.
Once these steps have been properly completed, the degree wheel will be set so that it reads zero when the number one cylinder is at Top Dead Center, and the dial indicator reads zero when the intake valve is fully closed. You are now ready to "Degree the Cam", using either of the following methods.
The centerline method does not require any special setup, but it does require some simple math, so you may want a calculator. Begin by rotating the engine clockwise until the dial indicator reads max lift. Set the dial indicator to zero and rotate the engine counterclockwise until the dial indicator reads roughly 0.100 inch down from max lift. This is done to take out any slack that may be present in the timing chain.
Note: You always want to hit your points by spinning the crank in the same direction it will rotate when the engine is running, which removes any variances created by slack in the timing chain. If your rings provide a lot of friction, it can be easy to go too far. If so, back up and try again. Just do not set the dial to 0.050 by turning the crank counterclockwise.
Continue by slowly rotating the engine clockwise until the dial indicator reads 0.050 inch before maximum lift (or zero) and record the number on the degree wheel. Next, continue to rotate the crankshaft clockwise through maximum lift (past zero) and onward until the dial indicator reads 0.050 inch after maximum lift (this is the closing side of the intake lobe), and again record the number on the degree wheel. Next, add those two numbers together and divide by two. The resulting number will be the location of maximum lift in relation to the crankshaft, which is known as the camshafts intake centerline. This number should be the same as the camshafts lobe center if the cam was ground straight up. If the numbers match, the cam is installed properly. If not, adjust the cam accordingly, either by advancing or retarding the camshaft.
Note: Many manufacturers, such as Comp Cams, grind their camshafts with 4 degrees of advance automatically added in. Clay Smith however, grinds their cams straight up, without any advance added in. If you prefer more bottom end power, we recommend installing your Clay Smith cam with 4 degrees of advance. In other words, if the cams lobe center is 110 degrees, you would install the cam with a centerline of 106 degrees. Or if the cams lobe center is 112 degrees, you would install the cam with a centerline of 108 degrees.
However, when you install a cam with advanced valve timing, you almost always lose a little top end power. If you do a lot of highway driving, and more top end power is desired rather than bottom end torque, you may choose to install the cam straight up. You can also make a compromise and install it with 2 degrees of advance. While the choice is totally up to you, Classic Inlines recommends installing the cam with 4 degrees of advance for most street or street/strip applications.
Rotate the engine in its normal direction of rotation while watching the dial indicator. As the lifter starts to move up the opening side of the lobe, the reading on the dial indicator will start to increase. Continue rotating the engine until the dial indicator shows .050" of rise. Stop and take a reading on the degree wheel and write it down.
As you continue to rotate the engine, the reading on the dial indicator will rise up to the maximum lobe lift. The lifter is now on the top of the lobe. The maximum lobe lift is often shown on the spec card and can be verified at this point if you wish. Continue the rotation and the lifter will start down the closing side of the lobe. Carefully watch the dial indicator as the numbers descend. When the indicator descends back to the .050" reading, stop and take another reading from the degree wheel and write it down. Then rotate the engine and return to the base circle of the lobe. The dial indicator must read zero again, to be sure the process was correctly done.
You now have the two important readings from the degree wheel, both taken when the dial indicator read .050", one BTDC and the other ATDC. One reading as the indicator was ascending on the opening side (BTDC), the other when it was descending on the closing side (ATDC). Compare these numbers to those on your cam card to verify the position of the intake lobe. The cam card will show the degree readings for the intake "opening" side of the lobe and the intake "closing" side of the lobe, when the dial indicator is at .050" of lift. Compare your readings for the intake to those on the card. If you're within a degree, your camshaft is installed in the correct position.
You can follow exactly the same procedure on the exhaust lobe to determine its opening and closing points at .050" of lifter rise, and compare the readings to those on the cam card. By checking the exhaust lobe, you will have four points of reference (intake opening and closing, and exhaust opening and closing) to go by. Remember, if you are plus or minus one degree of these readings, your cam installed properly and will be synchronized to the crankshaft's rotation.
In the next few weeks we'll be installing and degreeing a camshaft
in the motor
for the '66 coupe. We'll make sure to take plenty of pictures that we can post.
We may even make a video while we're at it. Who knows.....
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