We used a dial indicator on a cylinder-bridge tool to position TDC. You could also use a dial indicator with a magnetic base for this. Place the dial indicator over the cylinder and set the zero mark at roughly the piston's highest point. Rotate the engine counterclockwise to 0.100 inch down and then rotate the crank clockwise to where the piston is 0.050 inch down in the bore. Record the degree-wheel reading. Then continue to rotate the piston clockwise through TDC to 0.050 inch down on the dial indicator to the opposite side of TDC and read the degree wheel. The two numbers will be the same when TDC is positioned accurately.
We used a magnetic base and dial indicator with a short extension to read lifter travel. For accuracy, make sure the dial indicator does not bind throughout the entire lifter curve.
The size of the degree wheel will also affect accuracy. The larger the wheel, the greater the distance between each degree mark. Powerhouse sells a 16-inch-diameter wheel, but it also costs $180. When we rechecked all our measurements using JGM's Pro wheel, we found only one checking point-intake closing-was different by less than 1 degree. This led us to believe our small degree wheel was accurate.
With the cam, crank, timing set, and No. 1 piston and rod in place in the engine, the first thing to do is mount the crank nut on the crank snout, install the degree wheel, and position a pointer so it's very close to the degree wheel and lines up directly over an individual timing mark. There should be no question where it is pointing. This eliminates visual errors.
Next, rotate the crank until the No. 1 piston is close to TDC. Adjust the degree wheel to indicate TDC. This just has to be close. Now turn the crank about 50 degrees counterclockwise and mount your piston stop. For our Rat, we used a dial indicator on a bridge, but it works the same way. For a piston stop, merely rotate the engine clockwise until the piston contacts the stop and record the number on the degree wheel. Then rotate the engine the opposite direction until it hits the stop and record that number. If the degree wheel is located correctly (which it probably isn't), the numbers on either side of TDC will be exactly the same-let's use 24 degrees for our example (your number will vary). Most often, you'll get two different readings-say 26 and 22 degrees. Add the two numbers and divide by two, which in this case will be 26 + 22 = 48 / 2 = 24 degrees. Move the degree wheel to read 24 degrees against the stop and then rotate the engine back to the stop on the opposite side of TDC. It should read the same number.
This first step is the most important. If the TDC position is not correct, nothing else you measure will be accurate. Double-check your work up to this point. Once you have accurately established TDC, you can move on to actually degreeing the camshaft.
Get Your Degree
The next step is reading cam lift with a dial indicator. First, you'll need to position the magnetic base to the block and then mount the dial indicator. Next, you'll need a tappet of the same style as the cam. You can't use a roller tappet on a flat-tappet cam nor can you use a flat-tappet lifter on a roller cam.
Our cam for the fat Rat is a mechanical roller, but the procedure is always the same regardless of cam style. Do not place the tip of the dial indicator in the pushrod cup of the lifter to read lift. The lifter cup radius offers no flat area for repeatability. Instead, use the edge of the lifter or build a dedicated lifter with a flat that will accurately locate the dial-indicator plunger. Make sure the dial indicator travels roughly the same angle as the lifter. If the heads are bolted on the engine, you can use a pushrod to move the dial indicator
Once the dial indicator is set, run through the entire lift curve several times to ensure it always returns to zero. If it does not, this is usually due to binding between the lifter and the dial-indicator plunger. Reposition the dial indicator until the indicator always returns to zero. This is important for the accuracy of your test.
Now we need to talk about the timing card. In our case, we were degreeing a Comp mechanical roller cam. Comp's cam cards for mechanical roller cams list the opening and closing specs at 0.015 inch. Because these numbers are close to the base circle, it's difficult to create accurate measurements. This is why Comp prefers to degree cams by using the intake-centerline method. That procedure is detailed in the "Intake-Centerline Method" sidebar.