Engine Assembly, Part 4: The Camshaft
By Wayne Scraba/autoMedia.com
Degree of Difficulty
Finding True Top Dead Center
Before the camshaft can be degreed, you have to determine the true Top Dead Center (TDC) in the engine. Determining exactly where Top Dead Center is can prove tricky. The dilemma is that during piston travel, the piston dwells at TDC for several degrees of crankshaft rotation. Because of this, you must use a device to stop the piston in the same position on either side of TDC and take readings from a degree wheel (see the accompanying photos).
Here’s how it’s done: You’ll need a piston stop, a degree wheel and a fabricated pointer to get the job done. Degree wheels are relatively easy to find. Piston stops can be purchased or fabricated (ours is an old discontinued job from Moroso). A pointer is easy to fabricate. A good old fashioned coat hanger looped around one of the timing cover bolts and sharpened to a point on the opposite end works perfectly. Mount the degree wheel securely to the crankshaft snout, and rotate the engine by hand to approximately TDC. You can get close by watching the piston on cylinder #1. It should be at the top of the bore and the timing marks on the cam drive should line up (usually a pair of pip marks). Align the pointer you made with zero or Top Dead Center marked on the degree wheel.
Rotate the engine to move the piston down into the cylinder bore. Install the piston stop device over the piston in cylinder #1. Very slowly turn the engine clockwise (never use the starter motor to do this; you’ll definitely put a hole through the piston), rotating it until the piston comes up and stops against the bolt. Examine the degree wheel and write down the number of degrees shown by the pointer.
Hand-turn the engine counter clockwise (opposite direction) until the piston comes up and stops on the bolt again. Check the degree wheel again and write down the number of degrees it now reads. Add these two readings together and divide the final figure by two. As an example, the first reading could have been 42-degrees after TDC and when you turned the crank the opposite direction, it could have read 38 degrees before Top Dead Center. Adding the numbers and dividing by two results in a figure of 40 degrees. Bend your fabricated pointer so that it now reads 40 degrees. Alternatively, you can loosen the degree wheel (but be absolutely positive you do not disturb the crankshaft position) and move the wheel so that it now reads that amount. Retighten the bolts and rotate the engine again making sure that the readings on each side of TDC are equal degrees away from zero. If they are, the zero on the degree wheel will now be the true TDC point. Remove the positive stop device. You’ve determined True Top Dead Center.
How to Degree the Camshaft
In addition to the degree wheel, you’ll need a dial indicator and a stand in order to degree the camshaft. You’ll also need some means to turn the engine over at the back of the crankshaft, since the degree wheel will be taking up residence on the nose. We have a homebrewed tool for this job; however a set of bolts inserted in the crank flange (flywheel mount) make for a perfect spot to insert a large screwdriver or pry-bar to turn the engine over.
There are a number of ways to successfully degree a camshaft; however the Intake Centerline method is likely the most popular (and reliable means) with high performance and racing engine builders. The Intake Centerline is really the point where the intake valve reaches maximum lift. Installing a cam on the intake centerline is usually referred to as installing it “straight up,” where it is not advanced or retarded. If the camshaft is ground on (using the Crane camshaft we used as an example) 110-degree lobe centers (this is the separation between the intake and exhaust lobes on the camshaft), installing it straight up means that it is installed with a 110-degree intake centerline.
In order to determine the point of maximum intake valve lift, install a (lightly) lubed lifter or in the case of roller lifters, a pair of lifters in the respective #1 cylinder lifter bore(s). As you turn the engine over, keep an eye on the lifter(s). When the lifter reaches the lowest spot in the lifter bore, stop. It has reached the camshaft base circle. A dial indicator and stand must be attached securely to the engine (the deck surface is most often used). Often, the dial indicator plunger is too short and cannot reach the lifter. If that’s the case, mount the plunger tip directly on top of the pushrod. In either case, it’s important to make sure the angle of the dial indicator plunger is the same angle as the lifter or pushrod travel. The idea is to read "straight line" (linear) movement of these parts, so the plunger must be aligned properly. With the indicator in position, set the dial indicator to zero.
Next, hand-rotate the engine in its normal direction of rotation (usually clockwise) while watching the dial indicator. Once the lifter reaches maximum lift, stop. Turn the engine backward until the dial indicator reads 0.100-inch below maximum lift. At this point, rotate the engine by hand in the normal clockwise rotation. Turn it slowly and smoothly until the dial indicator reads 0.050-inch below maximum lift. Check the fabricated pointer and write down the number on the degree wheel.
Continue to turn the engine in the conventional direction of rotation (clockwise) until the dial indicator reads 0.050-inch below the maximum lift point, and then stop. You’ll actually see the lifter reach maximum lift as you turn the engine over. The idea here is to get a reading on the lifter as it goes down from this point. Take a reading on the pointer/degree wheel. Write down the figure.
You now have the two important readings from the degree wheel, both taken when the dial indicator read 0.050-inch. The first reading was taken as the indicator was ascending on the opening side, the other when it was descending on the closing side. Add those two numbers together then divide by two. The intake centerline of the camshaft is half the distance between those two readings.
There are some things to consider when turning the engine over. Try not to jerk the crankshaft as your turn it. You can back up and try again, however back it up at least one-quarter turn and start again. This will take up slack in the timing chain or lash in the gears that can have an effect upon the readings, causing an error. Alternatively, should you miss the stopping point, simply continue rotating the engine in the normal direction until you return to the desired point and start over.
Another consideration is this: Always use the same type and size lifter that your camshaft was designed for. For example, you cannot use a .842-inch diameter lifter on a camshaft designed for a .875-inch diameter lifter. You cannot use a conventional flat tappet lifter to degree a roller camshaft.
Finally, be sure to clean off any excessive lubricant from the lobes and lifters you use for checking. Thick oil, especially assembly lube (paste) can create false readings. Wipe the parts clean before checking, and remember to re-lubricate them when you are finished.
Altering Camshaft Phasing There are several methods of adjusting 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 (see the accompanying photos), allowing you to advance or retard the camshaft. There are also offset keys made for the crankshaft (not so common today). 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 on those camshafts that use a dowel pin for indexing.
In this build, a camshaft belt drive setup from Jesel was used. As we mentioned earlier, the Jesel belt drive offers a number of performance advantages and one in particular is ease in which you can alter cam timing (loosen four bolts and with a special spanner tool, you can advance or retard the cam timing).
In the end, no matter what methods you use, degree the camshaft once again to be sure it is correct. We usually degree the cam then check it twice before putting our tools away. It’s far better to be safe than sorry. Check out the accompanying photo captions for more information.