Degreeing a Camshaft and Why is it Necessary
Why Degree your Camshaft? Is it Necessary?
The term "Degreeing In Your Camshaft" means that you are making sure the camshaft position in the engine matches what the manufacure recommends for optimum efficieny and performance. This is the relationship of the valve events, or the opening and closing of the valves, in relation to where the piston is in the cylinder. A few degrees off, one way or the other, can affect the engine's operation dramatically.
If manufacures were perfect, all you would need to do is line up the marks on the timing chain sprockets.Top sprocket at 6 o'clock and bottom sprocket at 12 o'clock and the cam would be degreed. In reality, you are dealing with a group of components (camshaft,crankshaft,timing chain and sprockets), all with their own standards and tolerances. If any of these are off from the manufacture, performance will be affected. Without degreeing the cam you can never be sure that all the parts are in correct relationship. If you have the tools and expertise, we recommend that the camshaft's position in the engine be degreed in.
Is There More Than One Way to Degree a Cam.
Currently there are two popular methods for degreeing a cam: The centerline method, and the duration at .050" lift method.
Either method will work and is better than not degreeing the cam at all. But of the two methods, the duration at .050" cam lift (some manufactures also use .020, so adjust the below settings accordingly) is the easiest and the one I recommend.
The main problem with the centerline method is it has you have to find the theoretical centerline of the intake and/or exhaust lobe and line up on it. It makes the basic assumption that the lobe you are checking is symmetrical with its opening side being the exact same shape and size as the closing side of the lobe. The truth is that most modern lobes are asymmetrical, with the opening side of the lobe being much more aggressive and the closing side being more gentle. I>E. The Comp Cams Extreme series. Therefore, when you attempt to locate the middle (or centerline) of the asymmetrical lobe there is an automatic error factor. It could be off as little as 2° or as much as 6°, depending on the exact lobe shape and the procedure used during the degreeing operation. It also doesn't verify if the camshaft has been properly ground with the correct duration lobes, which can affect performance. Since the "duration at .050" lift method" is not affected by the asymetrical lobe design, You are mearly checking at .050 rise against the cam manufactures spec. I believe it is more accurate way to degree a cam.
What Tools will I need to Degree in a Pontiac Cam?
Basic tools required:
A degree wheel. You can also use an Aftermarket fully degreed balancer or install a degree tape of your stock Pontiac balancer. Be sure to get the tape that matches the diameter of your Pontiac balancer which is 5 1/4". Use whatever will give you accurate markings for 360°.
A pointer of some kind that can be conveniently mounted to the engine. I use a cut off coat hanger with on end wrapped around a 3/8" bolt to the water pump hole.
A 1" dial indicator with .001" increments. A rigid stand that mounts to the engine or with a magnetic base to hold the dial indicator will also be required.
A positive stop device to locate T.D.C. There are several ways to do this depending on whether you have the heads mounted or not. You can make your own by using an old spark plug. Remove the porcelain inside, drill and tap the interior of the spark plug housing and thread a long bolt through it. The other method is a flat piece of 1.5" X 7.5" metal 1/4" thick. Drill your holes for cross headbolt mounting and drill a hole in the middle to mount a bolt and nut to act as a stop.
Finding Top Dead Center. (T.D.C.)
Determining exactly where Top Dead Center can be tricky with some type of piston stop. The problem in finding the true T.D.C. of the piston's travel is that the piston dwells at T.D.C. for several degrees of crankshaft rotation. Especially with longer the rod ratios.
To Begin the procedure, first mount the degree wheel/degreed balancer on the end of the crankshaft securely and rotating the engine to approximately what looks to be T.D.C. Mount the pointer and line it up at zero on the degree wheel. Now rotate the engine to move the piston down into the cylinder. Install your positive stop device into the spark plug hole or the bar stop method. Now hand turn the engine (do not use the starter motor or you will put a hole through the piston), rotating until the piston comes up and stops against the bolt. Look at the degree wheel and write down the number of degrees shown by the pointer. Hand turn the engine in the opposite direction until the piston comes up and stops on the bolt again. Go back to the degree wheel and write down the degrees it now reads. Add these two readings together and divide the answer by two. Now either move your pointer by this many degrees, or carefully loosen the degree wheel (without disturbing the position of the crankshaft) and move the wheel this required amount. Retighten the bolts, and rotate the engine again making sure that the readings on each side of T.D.C. are equally degreed away from zero. On the balancer method you might have to relocated the tip of the pointer to get true TDC. If they are, the zero on the degree wheel will now be the true T.D.C. point. Remove the positive stop device and the procedure is complete.
A Simple Explanation of Cam Degreeing
In simple terms, degreeing a cam can be thought of as using a dial indicator and degree wheel to locate
opening and closing events around the cam lobe. You will start on the base circle of the lobe where there is no lift. See figure below.
Then by rotating the engine you will 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. You will watch the dial indicator, and stop at two key points to take readings from the degree wheel. Both points will be when the dial indicator shows .050" of lifter rise on the opening and again on the closing side of the lobe. These readings will then be compared to the manufacures "Cam" card to see how close you are. If necessary, corrections can be made to put the camshaft in the exact position.
Important Tips to Remember When Degreeing a Camshaft
You must always use the same style lifter that your camshaft was designed for. For example, You cannot use a standard (flat) lifter to degree a roller camshaft. However, you can interchange a solid or hyd lifter to degre eithr of those style of camscams.
Clean off any excessive lubricant from the lobes and lifters that you are checking. Any 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. Then re-check.
The Procedure to Degree the Camshaft
The dial indicator and stand must be attached securely to the engine. Any deflection could cause an error in your readings. Using the number one cylinder as a starting point, hand rotate the engine in a normal direction (clockwise, when standing in front of the engine) until the intake valve is closed (the lifter is down on the base circle of the cam lobe). If the intake manifold is off the engine, mount the plunger of the indicator directly on top of the intake lifter itself. If the intake manifold is on the engine, you can use the pushrod tip as an extension to the dial indicator and mount the indicator tip directly on top of the pushrod. In either case it is important to make sure the angle of the dial indicator is the same angle as the lifter or pushrod travel. We want to read "straight line" (linear) movement of these parts, so the plunger must be aligned properly. With the indicator in position, put a little preload (.020 or so) in the indicator and set the dial indicator to zero.
Hand 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 rise. Continue rotating the engine until the dial indicator shows .050". Stop and take a reading on the degree wheel and write it down. Now ou can look at the manufactures card to see if your readings match. But more before we change anything. Remeber change your readings if the manufacture uses .020.
As you continue to rotate the engine, watch and record the amount of rise on the dial indicator as it reaches maximum lobe lift. The lifter is now on the top of the lobe. (The maximum lobe lift is 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, take a reading from the degree wheel and write it down. 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 reading as the indicator was ascending on the opening side, the other when it was descending on the closing side. Compare these numbers to those on your camshaft inspection card to verify the position of the intake lobe. The camshaft specification card provides much information, but the numbers you are most interested in for the degreeing of the cam are at the bottom of the card. In the box identified as "Cam timing at .050" Tappet Lift". (Just a reminder, the word tappet and lifter mean the same thing. This can also be expressed as .050" lifter rise.) Inside this box are the degree readings that the degree wheel would show 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. (Below those figures are the opening and closing figures for the exhaust.) 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 and for normal useage you won't notice a degree.
You can follow exactly the same procedure on the exhaust lobe to determine its opening and closing degree points at .050" of tappet (or lifter) rise, and compare these readings to those on the specification card. If you also check the exhaust lobe you will have four points of reference (intake opening and closing, and the exhaust opening and closing) to go by. Remember, if you are plus or minus one degree of these readings, your cam is in the correct location and will be synchronized to the crankshaft's rotation.
What Do if Your Camshaft is Off in Location and Needs Correction?
There are several methods of adjusting the location of the camshaft to correct for misalignment. Most high performance timing chain sets Today have the lower crank sprocket machined with three or more keyways.
This allows you to advance or retard the camshaft. There are also offset keys made for the camshaft. Use any of the above methods. Then degree the camshaft once or twice more to be sure it is correct.