Perfect Timing

The Basics of Degreeing in a Camshaft

Mike Petralia Jul 26, 2002 0 Comment(s)

You just opened the box containing that new monster cam you bought for your hot rod and you can hardly wait to simply slide that baby in place. Piece of cake, you reason. It's going to make your car rump and shake like a Pro Stocker, and it's certain to produce more power than any other machine on your block. But is installing it really a no-brainer? Not exactly. If you install the cam correctly the first time, you will reap all of its rewards. If you don't, you'll be driving a heap. How do you know if it's installed correctly, you ask? Well, you can either rely on your keen ability to "see" within your engine and "read" the cam's figures as they actually occur. Or you can degree it.

Degreeing a cam is a simple and effective way to ensure you've got the cam you were looking for and you've installed it correctly. Even with today's cam companies using some of the best computer-controlled cam grinding equipment available, there's still the chance for operator error. The cam grinder could have machined the wrong lobes, or the packaging department could have put the wrong label on the box. Either way, you'd never know unless you degree the cam.

There's often confusion about what degreeing a cam really means. In its simplest definition, degreeing the cam is a means of verifying the installed position of the cam relative to the crankshaft; i.e. "advanced, retarded, or straight-up," and it's also a way to confirm that the cam was ground correctly. Degreeing a cam is not the same as advancing or retarding it as some people mistakenly believe. Degreeing the cam involves bolting a precisely-marked wheel onto the crank or damper, which will indicate crankshaft position, and then checking the cam lobes at a specified lift. Most degree wheels are numbered in 180-degree increments moving away from both sides of Top Dead Center (TDC). Although there are other ways to mark the degree wheel, such as 360 degrees from TDC and also in 90-degree increments, wheels marked 180 degrees on either side of TDC are generally the easiest to use.

FINDING TRUE TDC

This is the most important part of correctly degreeing your camshaft and if it's not done properly, your results will be worthless. Fortunately, it's also the simplest part of the process. Start with the No. 1 piston approximately at TDC. This can be done by placing your finger over the No. 1 spark plug hole and turning the crank clockwise until air pushes out. Watch the damper for the TDC or 0-degree mark to come up and stop rotating the engine when TDC is indicated on the damper. Install the degree wheel and align a fixed pointer (coat hangar wire works well) with the TDC mark on the degree wheel mounted on the crank snout or damper. Don't worry about getting it exact yet, that step is next. Now turn the crank counterclockwise until the wheel reads about 90 degrees and thread a positive piston stop into the No. 1 spark plug hole or strap a piston stop on the deck if the heads are off. Carefully turn the crank clockwise until you feel the piston touch the stop. It helps to have a hole drilled in your piston stop to bleed off cylinder pressure as the piston moves up the bore. With the piston touching the stop, mark the degree wheel or write down the number, i.e. 64 degrees. Next, reverse direction and rotate the crank counterclockwise until the piston touches the stop again and mark the wheel or write down that number, i.e. 70 degrees. The difference between these two readings is 6 degrees. Move the wheel or wire half that distance (3 degrees) to indicate 67 degrees on the wheel. Switch direction again and rotate the crank clockwise, and if you did it right, the wheel should indicate the same number when it touches the piston stop in either direction, i.e. 67 degrees in this example. Once you've got it stopping on the same point in either direction, the wheel will correctly indicate TDC with the piston stop removed. DO NOT MOVE THE WIRE OR WHEEL AFTER THIS POINT.

THE EASIET METHOD: CHECKING LOBE CENTERLINE

There are two common ways to degree a cam. The easiest is the lobe centerline method. With this method you can find out if you've installed the cam correctly and, to a certain extent, check to see if the manufacturer's grind is correct. Without changing your degree wheel or pointer position, rotate the engine until you see no movement on the No. 1 intake lifter, pushrod, or rocker arm. Use the longest ratchet or breaker bar you can when turning the engine for smooth movements. Short ratchets lead to jerky motions and inaccurate readings. You'll want to install a 1-inch dial indicator reading off the No. 1 intake lobe of the cam (second lobe in from the front on the driver's side of the engine). If your engine is fully assembled, it's easiest to use a pushrod as an extension for your indicator (see photos). You'll also need to use a solid lifter lubricated with engine oil only on the intake lobe; hydraulic lifters cannot be trusted to read correctly. Turn the crank clockwise until the indicator reaches maximum lobe lift. Zero the indicator at max lift point and rotate the engine clockwise two full revolutions to check that the gauge returns to zero. If it does not return to zero, check your indicator/pushrod alignment to be sure it is not binding. Starting at zero, reverse direction and rotate the engine counterclockwise slowly until the indicator passes 0.050. Stop around 0.090 (this step will eliminate any chance of timing chain slack affecting your readings) and switch direction to clockwise rotation. Slowly turn the crank clockwise, watching the indicator and stop when it reaches exactly 0.050. Write down the reading on the degree wheel, i.e. 64 degrees. Continue rotating clockwise until you see the dial indicator reach zero and start moving again towards 0.050. Slow down and stop exactly on 0.050. Write down this reading as well, i.e. 151 degrees. Add these two figures and divide the sum by two (64 + 151 = 215/2 = 107.5) This indicates your installed intake lobe centerline position. If this figure closely matches (+/- 1 degree) the intake lobe centerline indicated on the timing card that came with your cam (i.e. 108 degrees), it is installed correctly. If it came up higher, say at 112 degrees, you've installed the cam retarded (4 degrees in this case) or if the figure is lower, say 104, you've installed the cam 4 degrees advanced.

If your figures indicate that the cam is advanced or retarded and you have correctly aligned the marks on the timing gears showing the cam to be installed at "zero" or "straight up," then the cam was ground slightly off and you can correct its installed position a number of ways. The easiest is by repositioning the crank gear of an adjustable timing chain set. Or you can drill the cam gear's dowel-pin hole and install offset bushings to adjust cam position. Of course the easiest method is also the most expensive, but if you run a belt drive, you can quickly and repeatedly adjust the cam position at any time, without getting messy.

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.

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.

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.

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