Camshaft specs are arguably one of the most difficult parts of engine building to get right, from scratch. As such most of us rely on the experts to spec-out our bumpsticks for us. However, you don’t have to know how to spec a camshaft in order to make sure your camshaft is built to spec.
In this video from Pete’s Garage, he covers how to properly install your timing set, and then perform all the required checks to confirm that your camshaft – from Comp Cams, in this case – matches all the numbers on the card. The one thing Pete doesn’t do in the video, is check the intake centerline, which is traditionally the main check performed in the degreeing process.
However, make sure to read all the way through to the end of the article, as we explain both methods of checking that the camshaft is installed correctly, and and thanks to Pete’s thorough videography, we can actually calculate the cam’s intake centerline, even though he didn’t.
Finding Top Dead Center
As Pete covers in the video, the first step is to rotate the crank so that the number-one piston is slightly below it’s peak travel, on the upstroke. Then, with a dial indicator set up indicating on the crown of the piston, rotate the crank until the piston is at the absolute peak of its upward travel..
Once Top dead center is found, it’s time to install the timing set, making sure that the crank gear has the appropriate keyway aligned. In this case, it’s a nine-way gear, and Pete wants to install it using the 0-degree option. Then, making sure the timing mark is properly aligned on the cam sprocket, it is fastened to the camshaft using ARP bolts, some thread locker, and 35 lb-ft of torque.
Setting the Degree Wheel
Without a proper reference point, all of this would be for naught. A degree wheel is a handy tool that is easy to use, and should be in the toolbox of anyone who has ever rebuilt and engine. Pete has a unique setup in which the bolt that threads into the crank is internally threaded for the degree wheel mounting bolt. “The nice thing about putting a bolt inside of the actual crank bolt, is that I don’t have to worry that when I’m rotating the crank, that I’m moving the degree wheel at all,” he explains.
Once the piston is set to top dead center and the pointer is aligned at the TDC zero mark, Pete verifies the degree wheel’s accuracy by checking the degree wheel and pointer’s reading with the piston .020 inch in the hole, as indicated by the dial indicator, before and after top dead center. With both readings coming in at 8 degrees, the pointer and degree wheel are confirmed to be aligned.
With everything aligned, the first check to be performed is to check the intake valve event timing at .050 inch of lift. According to the cam card, the valve should open to .050 inch at 12 degrees before top dead center. Rotating the crank until the dial indicator – which has been positioned on the lifter, in line with the direction of movement of the lifter – shows .050 inch of lobe lift reveals 12 degrees BTDC on the wheel.
The next check is the intake valve closing event, at the same .050 inch measurement, but in the other direction. This one is called out at 44 degrees after bottom dead center, and the degree wheel indicates 44 degrees ABDC on the money.
Pete’s next check is to confirm the “duration at .050 inch” specification on the cam card. While this is essentially the same as the two previous measurements combined, not only does it verify duration at .050 inch (remember, check twice, and all that), but it also double checks the numbers to verify that the cam is installed in the proper position.
Once the 12-degree BTDC and 44-degree ABDC events have been confirmed and marked on the wheel, Pete counts of the degrees of rotation between the two. Somehow in his second measurement, he’s lost a degree, but that could be a simple math error, and the duration of 236 degrees at .050 inch checks out.
The final spec that Pete checks is the cam’s lobe lift. With the indicator still set up on the lifter, he zeros it out while the lifter is riding on the cam’s base circle, he simply rotates the crank until the camshaft lobe is at its peak lift, and records the reading on the dial gauge. In this case, the cam lobe measures .363 inches, which is exactly what’s called for.
Degreeing The Cam
While all of those checks ensure that the camshaft specs are what they are supposed to be, you also need to check that the camshaft is installed in the correct position. Whether you are installing it straight up at 0 degrees of advance or retard, as in this video, or if you are adjusting the camshaft’s installed position for optimum performance, you need to verify that it is actually where you think it is.
One method is by using the duration check that Pete did, and ensuring that the degree wheel readings for the opening at .050 inch and closing at .050 inch events are where the cam card specifies. Some argue that method to be better, as it is unaffected by an asymmetrical lobe design. In addition to comparing the intake opening and closing events to the cam card, you can also find intake lobe centerline from those numbers, with slightly more complicated math.
However that isn’t the traditional degreeing method, as suggested by Comp Cams. In the more traditional method, your goal is to find the centerline of the intake lobe. To do that, you find the peak lift of the cam lobe, just the same as in the video, but then locate points on the degree wheel .050 inch before and after the peak lift reading. You then add those two readings together, and divide by two, and that would be your intake centerline. Compare that to the cam card, and you can adjust cam timing with your timing set from there.
Regardless of which method you use, ensuring that your camshaft is installed properly and matches the specs on the cam card is one of those steps in engine assemble that some people see as extra and others as mandatory, but can be the difference between an engine that runs great, and one that just runs.