This article on how to degree dual overhead camshafts is intended to give the reader an understanding of the degreeing process.
Camshaft degreeing is the process in which the lobe center of the cam is adjusted to match a predetermine crankshaft position. Because this is basically done by means of a protractor and in degrees represented by the protractor the expression of camshaft degree, cam degree or degreeing cams stuck.
Adjustable cam gears.
Adjustable cam gears are required to degree dual overhead camshafts. It helps in the process of adjusting the intake and exhaust cam separately from each other so that they open and close at the correct moment. Adjustable cam gear allows the engine tuner or engine builder to move the crankshaft in small increments whilst the camsshafts remain stationary or vice verse. The process of camshaft degreeing insures that maximum lift correspond to a desired crank position. The center line or the point on the cam where maximum lift occurs is known as lobe center.
Lets say the advertised lobe centers for a set of 264º camshaft is 110 for the inlet cam and 103 for the exhaust cam. Adjusting your cams too these specs will most probably bring them very close to their maximum designed performance. A lobe center of 110 on the inlet cam means that maximum valve opening will be at 110º ATDC and 103 on the exhaust will mean that maximum valve lift will be at 103º BTDC
How to degree dual overhead camshafts.
The process of camshaft degreeing almost always starts with the adjustable cam gears set at the zero position and the camshafts installed to match factory specifications.
1. Use a pencil, paper and arithmetic for this procedure, to keep track of the results.
2. Fashion a rigid pointer from stiff wire or an old coat hanger and attach it to the engine block. This pointer locates the degrees on the degree wheel.
3. With a degree wheel installed on the crankshaft, rotate the crank to get the no 1- piston at TDC and check to ensure that the valves are fully closed then adjust the pointer to zero (0º TDC) on the degree wheel. (Free Degree Wheel)
4. Turn the crankshaft opposite the running rotation approximately 15-20 degrees. Install a piston stop on the top of the engine block fastened in place by two head bolts or in the case of overhead cams install the piston stop into the spark plug holes. Note: A dial gauge can also be used.
5. Continue to turn the engine in the same direction until the piston comes back up and just touches the piston stop. Make a note of the exact number on the degree wheel that the pointer is on.
6. Rotate the engine in the other direction (running rotation) until the piston comes back up and touches the piston stop. Again note the number where the pointer is.
7. Remove the piston stop and rotate the crankshaft to the midpoint of the two marks. At this point the piston is at the true top dead center. Loosen the degree wheel and adjust it so it will read 0º TDC at the pointer. Don’t rotate the crankshaft to do this!
8. Now, it’s time to locate the lobe center line relative to TDC. Attach a dial indicator on the top of the engine block. Set the tip to contact the top of the no 1-cylinder inlet valve shim/bucket. Check to make sure that the indicator plunger is parallel to the valve stem. NOTE – any variance in an angle will produce geometric errors in the lift readings.
9. Rotate the engine in the normal direction of rotation until a reading on the dial gauge of 0.040? lift is reached. (Valve will start to open) Mark the dial gauge and make a note of the reading on the degree wheel.
10. Continue to turn the engine in the normal direction past maximum lift. The valve will now return to its close position. Make a note of the degree wheel reading when the indicator reads 0.040″ on the return side
11. Now add the larger of the two readings that you noted on the degree wheel to 180 subtract the smaller number and then divide the answer by two. Your answer will indicate the lobe center of the cam. Example: open reading was 4 and closing reading was 43. Now add 43 to 180 = 223, subtract 4 = 219 divide by 2 = 109.5. Lobe center is 109.5 degrees.
12. Continue to move the cam on the adjustable cam gear and redo steps 10 to 12 until the required lobe center is achieved.
13. Now do the same for the exhaust cam
The abbreviation for dual or double overhead camshafts is DOHC