Jan. - Feb. 1996 Lane Racing And Rodding Article By Jim Kaekel, Jr.
One of the most commonly overlooked phases of engine building involves "degreeing" the camshaft. Generally, most novice engine builders will install a cam "straight up" by simply aligning the timing marks of the cam and crank sprockets.; While the "straight up" method may be fine for the family mini-van, it certainly is not the ticket for a performance engine. Cam degreeing is just one more way to exercise your performance dollar.
Because of tolerances in the location of dowel pins and keyways, it would be rare that you would find a cam exactly on the cam manufacturer's recommendations after installing it "straight up" and then degreeing it. The manufacturer's recommendation, along with duration, valve lift, and timing, is located on the specification card, packed with the cam.
Actual characteristics of the cam can be changed somewhat by advancing or retarding it. Advancing the cam would simply open the valves sooner and, therefore, close them sooner. This will generally increase bottom end horsepower while sacrificing top end. Retarding the cam would then open the valves later, reducing bottom end power but increasing top end power. Remember that it is always best to start at the manufacturer's recommendation and get a base before making changes.
Most cam manufacturers recommend using the "Intake Centerline" method for checking cam "phasing." The intake centerline is the point that the intake valve reaches maximum lift. By checking this phasing, you can determine the piston and valve relationship.
To degree a cam by this method, you would begin by installing the cam in the normal "straight up" position. Next, install a quality degree wheel such as the Mr. Gasket Pro Wheel (#9120) on the crankshaft snout. Crane Cams offers a Tune-A-Cam Kit (#99030-1) that comes with a degree wheel, piston stop, pointer, checking springs, dial indicator and stand.
After the degree wheel is installed, turn the engine over and locate Top Dead Center on the number one cylinder with a dial indicator. You will then need to fabricate a pointer (usually a piece of coat hanger wire under a timing cover bolt will do) and point it at TDC on the degree wheel.
Next, place a lifter on the intake lobe of the number one cylinder. Place a dial indicator on the edge of the lifter so that it will have enough travel when the engine is turned over. Slowly rotate the engine until the lifter rises to maximum lift and "zero" the indicator. Back the engine up until the indicator falls .050" past maximum lift. Turn the engine forward until the indicator reaches .050" before maximum lift and mark this point on the degree wheel. Continue turning the engine forward until the lifter rises to maximum lift and falls .050" on the back side and again mark the wheel. Half way between these two marks is your intake centerline.
To change the "phasing" you will need to purchase a set of degree bushings for your particular engine (again, Crane, Competition Cams and Mr. Gasket come to the rescue). The bushings are installed in the cam gear after the dowel pin hole is drilled oversize. These bushings are made offset in different increments to allow you to advance or retard from your initial reading. Several companies make timing gear sets with multiple keyway crank sprockets as another option for altering cam timing. Be sure to always degree the cam again after changing bushings or crank sprocket locations.
While degreeing a cam at first may be confusing, you will find that after time, it will come easier. Competition Cans even makes a video on degreeing ( #190-1) for those of you who like to play "couch potato" and learn at the same time.