Degreeing a cam involves simple...
Degreeing a cam involves simple math, but you will need to write down your readings. We like to use this laminated sheet from Lunati that has the formulas right on it. We use a grease pencil, commonly called a "China Marker," available at most art stores, to write on it. That way the numbers can be easily wiped off with a rag later.
Checking At 0.050 Method
What the Intake Centerline Method cannot tell you is if the cam's duration was correctly ground at the factory. Although, if the lobe centerline came up exactly as the cam card called for, you can bet that it was ground correctly. If you feel the need to check further, do not change the position of the degree wheel or pointer. Rotate the engine clockwise until you see no movement at the lifter or pushrod. Zero it at this point, which is on the cam's base circle. Rotate the engine clockwise and stop exactly at 0.050 and take a reading on the degree wheel, i.e. 12 degrees before top dead center (BTDC). Continue rotating clockwise while counting the number of revolutions the indicator makes.
Stop when max lobe lift is reached, usually between 0.300-0.400 inch (3-4 revolutions on a one-inch indicator) and take a reading, i.e. 0.312, to compare the lobe lift figure on the cam card. Keep turning the crank clockwise and count the number of revolutions the indicator makes. Slow down after it passes zero on its last revolution and stop at 0.050 exactly. If you miss 0.050 on the way down, stop and rotate counterclockwise past it to around 0.090 and then switch to clockwise rotation again and stop at 0.050. Take your last reading here, i.e. 46 degrees after bottom dead center (ABDC). Compare these figures to the cam card to see if it was ground correctly and if you've installed it properly.
The cam card supplied with...
The cam card supplied with your cam is the source for all the information you'll need to check your readings against. Typically, it will show recommended installed position for the cam, lobe, or valve lift (valve lift is lobe lift multiplied by rocker arm ratio), intake lobe centerline, intake and exhaust opening and closing, duration at 0.050, and possibly seat duration which is usually calculated at 0.006-inch lift. This one from Erson also shows overlap.
What if the cam was installed 2 degrees advanced or ground incorrectly? The readings would then be as follows: 14 degrees (12 + 2 = 14) BTDC and 44 degrees (46 - 2 = 44) ABDC. The figures moved 2 degrees, but still have the same overall duration. Remember that when you're degreeing a cam, you're actually reading degrees of crankshaft rotation. So if you advance the cam, the valves open and close sooner in relation to the crank's position, and they open and close later if you retard the cam.
Total duration at 0.050 can be calculated by adding the sum of your two readings (12 + 46) or (14 + 44)-both equal 58-plus 180 degrees for crankshaft rotation because the cam spins at half the crank's speed. This equals 238, which should match the "duration @ 0.050" figure on the cam card. If this figure is off by less than 2 degrees, don't worry, unless you're a perfectionist. It won't even be noticeable in the car.
How Do You Read That?
Degree wheels come in many different sizes, but they all have the same shape-round. They can be marked in several ways, with the most common being 180 degrees away from TDC as shown. Marking in this fashion makes readings more sensible when degreeing the cam. Some of the professional wheels are marked off in 360-degree or 90-degree increments. These types of wheels look cool and are usually a much larger diameter lending to more accurate readings, but also require more math to use and should be avoided by the occasional cam degreer.
This Comp Cams degreeing kit...
This Comp Cams degreeing kit includes everything you'll need to degree cams all in one handy plastic storage case. It also includes written instructions and a video tape you can view either before or during the degreeing process to familiarize yourself.
Wheels like this Crane/Cam dynamics unit pictured also have shaded areas indicating lobe centerline, intake opening/closing, and exhaust opening/closing. All these areas help to more easily identify the position of the cam so your readings don't get confused. Look closely and you'll also notice that the bottom half of the wheel is numbered away from BDC on its inner shaded ring. This area is clearly marked as "intake closing-ABDC and exhaust opening-BBDC." This particular wheel also includes several useful cam-degreeing formulas right on its face. These formulas help you calculate overlap, intake and exhaust duration, intake centerline, and exhaust centerline.
Steps To Perfect Timing
Intake Lobe Centerline MethodFind TDC and secure degree wheel/indicator.
Zero indicator at max lobe lift.Rotate counterclockwise past 0.050, then clockwise to 0.050 and take reading.
Rotate clockwise past max lobe lift to 0.050, take reading.Add readings, divide sum by two.This is your intake lobe centerline.