Before any calculation can...
Before any calculation can be done, you need to find true TDC on the No. 1 cylinder. Pletcher mounted a positive stop tool onto the cylinder so he could find TDC.
Pletcher then hand-rotated the engine clockwise until the piston made contact with the positive stop and recorded the degrees indicated on the degree wheel. In this case, it was 38 degrees before top dead center (BTDC). Next, the engine was rotated by hand in the opposite direction, counter-clockwise, until it once again made contact with the positive stop. This time, the measurement was 32 degrees after top dead center (ATDC). Add these two numbers (38 degrees BTDC and 32 degrees ATDC) together and divide by 2 (38 + 32 = 70/2 = 35). Without turning the crankshaft, move the pointer to the 35-degree ATDC mark on the degree wheel. To check that the pointer was properly set, Pletcher hand rotated the crankshaft in both directions, touching the positive stop to make sure the pointer hit the same spot on the degree wheel. Now the degree wheel and crank, when set at the zero-degree setting, marks the true top dead center of the No. 1 piston.
At 0.050 Of An Inch Next, Pletcher inserted a lifter bore dial indicator into the No. 1 cylinder intake lifter bore to measure the lift on the lobe. Make sure you are measuring the intake lobe-if you are measuring an exhaust lobe, the numbers you get will be crazy. When doing this, make sure there isn't any grease-like break-in lube on the lobes, which can skew your readings on the degree wheel.
Pletcher then hand-rotated the engine clockwise, the normal operating direction (opening side of the lobe) until the dial indicator read 0.050 inches of lift, the industry standard checking height. Pletcher recorded the reading indicated from the pointer on the degree wheel, matched it to the cam card and then hand-turned the crank clockwise again to verify the maximum lift on the cam card. As the dial indicator started to decrease, Pletcher stopped rotating the engine at 0.050 inches on the closing side of the lobe. Once again, a reading was taken and recorded from the degree wheel and matched to the cam card. Pletcher continued to rotate the engine to make sure the dial indicator returned to zero at the base circle side of the lobe. Using these two readings, you can verify that the cam is matched to the cam card's specs. "I always repeat this a minimum of twice," Pletcher said. "There's always a chance that the dial indicator slipped or the degree wheel came loose on the crankshaft. Checking your work to make sure you get the same readings will prevent problems later on."
Confirming Duration We wanted to check some of our measurements to see how they matched our cam card. To calculate duration on the No. 1 intake lobe, we took our readings at 0.050-inch and found they were 27 degrees BTDC (opening) and 59 degrees after bottom dead center (ABDC, closing). To calculate duration, add these opening and closing values (27 + 59 = 86), and then add 180 (180 is the number of degrees between TDC and BDC). This (86 + 180 = 266) equals 266 degrees duration. To find the intake lobe centerline, divide the duration (266) by 2, and then subtract the opening value (27 degrees): 266 / 2 = 133 - 27 = 106 degrees intake lobe centerline. Apply the same formula to get the exhaust lobe values, if you choose to check them.
A lifter bore dial indicator...
A lifter bore dial indicator is used on the intake lobe of the No. 1 cylinder to check when the lifter is at 0.050-inch of lift on the opening side of the lobe and the same on the closing side. At these points, the degrees are checked with the manufacturer's specification on the cam card.
In order to perform the task of degreeing a camshaft, you will need the following tools:
* A degree wheel. It is best to pick the largest degree wheel you can find. The larger the wheel the more accurate it is.
* A pointer to point at the degree wheel. The pointer should have a stable base that can be attached to the engine block where it will not move.
* A dial indicator with a stable base. This needs to read in 0.001-inch increments at a 11/42-inch of travel.