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HOW TO DEGREE A CAMSHAFT

HOW TO DEGREE A CAMSHAFT
 

Most performance camshafts do not have to be degreed in order to work. Degreeing is a procedure used by engine builders to optimize engine output. It is a useful way to verify correct engine assembly, and to fine tune a racing combination. If you change the cam timing, be sure to recheck piston to valve clearance. The minimum clearance is .100.

 

TOOLS REQUIRED

The degreeing procedure requires a degree wheel, a pointer, a dial indicator, and a piston stop. The degree wheel and dial indicator are machine shop tools which must be purchased. The pointer may be purchased or fabricated from a piece of wire rod. The piston stop may also be fabricated. The crankshaft, camshaft, timing chain, and the rod and piston for the number one cylinder must be installed in orderto degree the cam. Mount the degree wheel to the front of the crankshaft. Install the pointer on the engine so that it points to the zero on the degree wheel when the number one piston is at the approximate top of its travel. This initial mounting location is only used to get “in the ballpark, the exact Top Dead Center position will be determined in our next step.

 

ESTABLISHING TOP CENTER

The first task is to accurately locate the Top Dead Center (TDC) of piston travel in the number one cylinder.

Although it is possible to do this with the heads on the engine, it is more easily done before they have been installed. Install the piston stop on the number one cylinder, and rotate the crankshaft until the piston contacts the stop. Mark this spot on the degree wheel, and then rotate the crankshaft in the opposite direction until it contacts the stop again. Note the degree wheel reading. Add up the number of degrees in the narrow angle separating the two points where the stop was reached, and divide the number by two. This number of degrees will tell you where to locate the center point in between the two positions. This center point position is the actual Top Dead Center (TDC). Mark this position on the degree wheel. Remove the piston stop and rotate the crankshaft until the TDC mark lines up with the pointer. Loosen the bolt holding the degree wheel, reposition the wheel so that the zero mark is perfectly lined up with the pointer, and tighten the mounting bolt.

 

MEASURING THE RELATIONSHIP OF THE CAMSHAFT TO THE CRANKSHAFT

Once we have located Top Dead Center, we can compare the position of the camshaft to that of the crankshaft. Camshafts are designed so that the valves open and close at specific intervals as the crankshaft rotates. The relationship between the two shafts is expressed as the variance from designed specifications, in degrees. (Note - Most camshaft specifications are expressed in crankshaft degrees. The crankshaft rotates twice for each single turn of the camshaft.) The reference point used for comparison is the intake lobe centerline of the cam. This spot, on the cam's number one intake lobe, is located through a similar procedure to that used to find Top Dead Center A solid lifter is placed on the number one cylinders intake cam lobe. A steel ball, the same diameter as the pushrod end, is set into the lifter. A dial indicator is set up against the ball, to read the lifter's vertical movement as the cam rotates. Set the indicator to read near zero at a point close to the maximum lift position of the cam lobe. Rotate the cam through the high part of the lobe, noting on the degree wheel the two spots where a reading of .050 below maximum lift appear on the dial indicator, once on the lifters way up on the lobe, the other on the way down. The lobe's centerline will be located in the exact center of the two equal indicator reading points. (Note - This may not correspond to the point of maximum lift.) This centerline's position, as indicated on the degree wheel, can be compared to specifications. A camshaft which specifies the intake centerline to be at 108 degrees after TDC, but which is at 104 degrees after TDC when checked, is considered four degrees Advanced. If the same cam checked out at 110 degrees after TDC, it would be two degrees Retarded. Advancing the cam from specifications will improve lower RPM performance at the cost of high speed power. Retarding the cam will enhance top end power, but will sacrifice low speed torque. While cam timing adjustment can be a useful tuning aid, it is not a substitute for correct camshaft selection. We offer timing sets featuring multiple keyways, which permit altering the cam timing without the use of fragile offset keys or bushings..

 



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