Ford Camshaft Timing - Degreed To Go

The degree wheel, which attaches to the crankshaft, tells you in degrees where the crankshaft is positioned relative to its 360-degree journey. Zero degrees is TDC. It's also 360 degrees when we make one full revolution of the crankshaft. All we have to do is establish TDC on the No. 1 cylinder. It doesn't have to be that cylinder, however; it can be any one you choose. Just make sure you're on the compression stroke at TDC for that particular bore when setting the degree wheel at zero.

Once you have TDC dialed in, don't disturb the degree-wheel position on the crank, as that will change TDC accuracy and throw off everything, forcing you to start over.

This entire setup includes a degree wheel from Comp Cams and the dial indicator. The dial indicator measures lobe lift off of the base circle. When we read the degree wheel, we get duration. It's a good idea to measure duration two ways-off the base circle and from 0.050 inch to 0.050 inch. To ensure accuracy, check lift and duration twice on each cylinder and record your findings with each.

After establishing zero degrees at TDC, roll the crank one full turn (360 degrees), and make sure the degree wheel is properly positioned. Now you're ready for cam timing.

Locate the manufacturer's cam-specification card. The cam card will tell you exact valve opening and closing specifications (duration). To confirm accuracy, you need a dial indicator with a measuring range of at least 1 inch on each lifter. With both valves closed, set the dial indicator at zero. Begin with the intake valve; slowly turn the crank clockwise until the lifter rises 0.050 inch. Stop turning the crank and read the degree wheel. This begins duration at 0.050 inch. If our cam card says the intake valve opens at 31 degrees BTDC, the degree wheel should show 31 degrees BTDC at this time.

On a cylinder-by-cylinder basis, record your reading. Slowly rotate the crankshaft clockwise and watch the lifter rise to the top of the lobe and then record lift. Continue turning the crankshaft and stop when the lifter reaches 0.050 inch above zero (base circle). Our cam card says intake closes at 67 degrees ABDC; we should see 67 degrees on the degree wheel. Repeat this procedure on all eight intake lobes.

Once you've checked and recorded all intake lobes, look over your findings with the cam card. Don't be surprised to find readings that are off 2-4 degrees from cam-card figures. Sometimes it's the camshaft and sometimes it's your crankshaft keyway. The crankshaft keyway should be in perfect alignment with sprocket timing marks at 12 and 6 o'clock. You have options that will get your timing spot on. We'll get into those shortly.

Repeat the same procedure on each of the exhaust valve lifters and record your findings. See how they compare with the manufacturer's cam card. Again, slowly turn the crank with each lobe and carefully document your findings. Every lobe should yield the same findings.

Advancing valve timing raises cylinder pressure because both valves close earlier. This should improve low and midrange torque. Retarding cam timing improves high-rpm performance, sacrificing low-end torque. For street performance, it's a good idea-depending on the camshaft-to advance timing 2-4 degrees. This should improve overall performance. Pay close attention to piston-to-valve clearances whenever you're advancing or retarding cam timing. This is a lot of work, but so is building another engine because you didn't catch all the details.

A Homemade Degree Wheel Forty years ago, Marvin McAfee of MCE Engines in Los Angeles fabricated his own billet-aluminum degree wheel because no one offered anything like it in the marketplace. He takes it further with not only degrees, but fractions of a degree for extreme accuracy. As McAfee dials in a camshaft, he makes notations on the degree wheel with a felt-tip marker. After recording his findings, he removes the markings with lacquer thinner and a rag. Note the custom fabricated pointer, too.	When advancing or retarding cam timing, always check piston-to-valve clearances with a head temporarily bolted into place. Mold modeling clay into the valve reliefs and observe valve impressions. Minimum valve-to-piston clearance is 0.060 inch. Ideally, you will have more.	Here, we have advanced cam timing at the crank by 2 degrees (2A). Rotating the crank gear to the proper advance (A) or retard (R) timing marks is an easy way to achieve the needed timing correction.
Another way to advance or retard cam timing is at the cam itself. Drill out the pin hole per the manufacturer's directions and use the appropriate offset eccentric. Kits typically include five eccentrics-five different advance and retard positions.	Another option is an offset crankshaft key, available in various advance or retard positions, which enables you to advance or retard the crank sprocket.	One method of advancing or retarding valve timing is a double-roller timing-chain set with an adjustable crank sprocket. Advance or retard valve timing as much as 8 degrees by moving the sprocket clockwise or counterclockwise around the crank Woodruff key. This mandates extreme caution. Check valve-to-piston clearances. We advance or retard cam timing to modify where we want power to happen. However, sometimes cam indexing from the manufacturer is off enough to warrant advance or retard depending on valve timing events.
Here's a good example of valve overlap on a degree wheel. Note the exhaust valve open and close time as it segues to intake valve open. This is called valve overlap, where we take advantage of intake velocity and exhaust scavenging. This helps cylinder pressure at high revs.	Crank degrees also show up on the harmonic balancer. This is total ignition timing at 3,000 rpm-in this case, 34-36 degrees BTDC.	Another important issue when addressing camshaft lobe lift is rocker-arm ratio. When it's 1.6:1, there's 1.6 times the lift than at the cam lobe. There's lobe lift and there's valve lift. Based on rocker-arm ratio, there's always more lift at the valve than at the lobe.