How To Degree Cams

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DOING IT

There’s more than one way to degree cams but the centerline method is the most common. There are even multiple ways to perform the centerline method. However, the following procedure is arguably the most common. 

As explained, a cam may reach peak lift for several degrees of crankshaft rotation. Therefore, finding a cam’s peak lift won’t necessarily reveal its centerline. In order to find its centerline, you’ll need to locate the exact midpoint between when a particular valve opens and when it closes. For dual-overhead cam engines, the procedure must be followed twice — once for the intake and once for the exhaust. Typically, measurements are taken on the number one cylinder’s valves.

Step 1: Begin by positioning the number one piston at TDC using the engine’s and crank pulley’s marks and fasten the degree wheel in front of the crank pulley with its TDC mark pointing up. Remove any covers or other accessories to allow the wheel to sit flat. All of this is easiest with the engine on a stand but can also be done anywhere so long as you can fit the degree wheel into place and still read it.

Most degree wheels are designed for clockwise-spinning engines. This degree wheel was relabeled to make cam degreeing counter-clockwise-spinning Honda engines a bit less painful.

Step 2: Find a short piece of welding rod or a metal coat hanger, bend it into a “J” shape, and sharpen its long end to a point. Slide a bolt through its bent end and fasten it to the engine near the degree wheel. Bend the rod so that its sharpened end points toward the degree wheel’s TDC mark.

A piece of aluminum welding rod bent and fastened to the block makes for a good reference pointer.

Step 3: When degreeing cams, never rely on the engine’s pulley, block, or timing belt/chain cover marks to pinpoint TDC. Variables like block height, inconsistent keyways, and piston dwell often make such methods inaccurate by as much as five degrees. Instead, use the piston-stop method to determine precisely when the piston’s reached its absolute highest point as well as the middle of its dwell. Begin by rotating the crank approximately 15 degrees in its normal operating direction so that its number one piston is just past the approximate TDC location you found earlier. Thread a piston-stop into its spark plug hole until it touches the number one piston. If you don’t have a piston stop, you can use a customized spark plug or fabricate your own piston stop out of anything rigid that threads into the spark plug hole and touches the piston just past TDC. 

You can buy a fancy piston stop or make one out of an old spark plug and some spare hardware. Just about anything that’ll thread into the spark plug hole and prevent the piston from reaching TDC will work.

Step 4: Continue to rotate the crank in its normal direction of rotation until the piston contacts the piston stop and record the degree wheel value corresponding with the pointer. Rotate the engine in the opposite direction until the piston contacts the piston-stop again and record that value. If both figures are the same, you’ve lucked out and have already located TDC. Usually, though, those two numbers will be different. True TDC lies halfway between them. For example, say that you’ve first recorded 26 degrees BTDC and then 22 degrees ATDC. Add the two numbers together, divide the result by two, and you get 24. Next, reposition the pointer halfway between the two, which in this case is exactly 24 degrees apart from each previously recorded value. Be sure that the pointer is dead-on and don’t disturb it. The math should appear as follows:

First Reading (26° BTDC) + Second Reading (22° ATDC) = 48° 

48° / 2 = 24°

Step 5: Remove the piston stop and rotate the crank so that the pointer lines up with the degree wheel’s TDC mark. You’ve now accurately located TDC and, chances are, it’s not where your timing cover and crank pulley say it should be. If you’re not sure that you did this step correctly or your wire or crank get bumped out of position, start over. The cam degreeing process is only as accurate as its initial TDC location.