Degreeing a Camshaft

January 17, 2010 CamshaftEngine

HOW TO DEGREE IN A CAMSHAFT ON A PONTIAC 326-455

 

For my 400 engine rebuildI chose the Competition Cams 270H camshaft. It has a lift of .470″ on the intake and exhaust. With Magnum Roller Rockers it is .006″ higher. The cam is designed to be positioned straight up, that is, dot to dot, on the timing sprockets. If it measures correctly, straight up will match the recommended 106 degree intake centerline of the manufacturer. (By the way, it did.)

 

There are several ways to degree a cam. This is my version. As indicated above, my engine is a 400. The following method worked exceptionally well for me and applies to when you have the heads off the block .

 

How to do it

 

Step 1. Align the timing sprocket dots for straight up. The cam sprocket dot should be at 6 o’clock and the crank sprocket dot at 12 o’clock high. [This is the easiest way to get the sprockets aligned because they are close to one another. It can als be performed with both at 12 o’clock.] Use a straight edge to help with the alignment. Take your time. When the crank key and sprocket and cam key and sprocket are in proper position slide both toward the engine in matching increments. At some point, the tight fit will require taping with a plastic hammer. Light taps… alternate between the crank and cam gears and avoid hitting the chain. If the gear is too tight a fit to start, heat the gears and chain in the oven. Raising the temperature to 130 degrees will make a big difference. Also, put a light coating of anti-seize on the cam hub and crank hub. This will aid assembly and permit removal if you need to pull the assembly apart to advance or retard the cam.[I used a true roller timing set. with 3 key ways; the sprocket was installed on all three to verify the accuracy of the set. It proved to be accurate on all keyways. I chose the middle keyway to give me the 106 degrees specified by Comp Cams. Note that the 270H and other Comp Cam grinds are manufactured with 4 degrees advance. Lobe separation angle is customarily 110 degrees with these grinds.] Once the sprockets are in place, double check the dot alignment by rotating the crank a few times to verify alignment. If everything checks out, proceed to Step 2.

 

Step 2. Hook up the Degreeing Wheel. Put TDC at 12 o’clock noon and fasten it on with the crank bolt. Also pick the right timing cover bolt hole to fasten your “coat hanger wire” degreeing wheel pointer. After cutting an appropriate length of wire, sharpen one end on a grinding wheel (or use a file) as this will provide an accurate pointer. Bend the wire so that it is at or near the 1 o’clock position on the crank. With my method, the wire will be repositioned several times. Go to Step 3.

 

Step 3. The piston stop. If the heads are on the block you must use a piston stop through the spark plug hole on the # 1 cylinder to locate TDC. [A spark plug piston stop requires a different procedure–not described here.] If you are rebuilding your engine or have the heads off so that you can see the pistons, a top of the block piston stop will be requred. These stops can be purchased from Crane, Comp Cams, Jegs, Summit, Powerhouse and local speed shops or simply fabricated from a piece of 3/16 inch steel. The steel strap must have three holes drilled into it. Two at each end to secure it to the head, and one in the middle. The stop will be positioned across the top of the cylinder bore and secured with the 5/8 inch head bolts with locking nuts. A whole in the middle of the strap should be fitted with a smaller bolt, e.g. 1/8 inch bolt with nuts and washers. Position the small bolt so that bolt head will contact the top of the piston. It is wide and will not mar the piston surface. Once the top of the block piston stop is screwed in with the bolt head protruding into the bore you are ready to find top dead center (TDC).

 

Step 4. Finding TDC. Rotate the crankshaft clockwise until the piston stops against the bolt head. Next, reposition the wire pointer to TDC on the degreeing wheel. Be accurate. Then, rotate the engine counter-clockwise (opposite direction) until it stops against the bolt head. Examine the pointer and compare it to the numbers embossed on the degreeing wheel. Divide the figure in half. [Example: degree wheel shows 32 degrees. Half of that sum is 16 degrees] Move the pointer to the half way point between the number and TDC on the wheel. [The pointer will be positioned to16 degrees.] Now, if your calculation is correct by turning the crank the opposite direction, clockwise, the stop should be on same number on the other side of TDC. [The piston should stop at 16 degrees]. If the two integers [e.g., 16] are the same you have found TDC. Now, remove the piston stop and turn the crank until TDC on the degreeing wheel aligns with the pointer. Do not disturb the pointer. [I also verified TDC by using a dial indicator on the number 1 cylinder.] Once you are certain that you have located top dead center, proceed to the step 5.

 

Step 5. Maximum Lift and Intake Centerline. Install an unoiled hydraulic lifter on #1 intake. Set up the dial indicator so that you can measure the amount of lift on the lifter. Everything needs to be perpendicular and properly aligned. The indicator shaft should sit on the lip of the lifter (not in the cup). Once this is properly aligned, rotate the crank clockwise until the lifter is on the bottom (base) of the cam lobe. This is the lowest point so the dial indicator can now be set to 0. Begin rotating the crank until you reach maximum lift (.313 on 270H). At maximum lift, reset the dial indicator to 0. Now rotate the crank in the opposite direction, smoothly and very slowly, stopping at .100″ below maximum lift. Now, reverse rotation until the dial indicator reads .050″ before maximum lift. Take a reading off the degreeing wheel and mark that number on the wheel (or use masking tape and write it down on the wheel). Continue rotating the crank past maximum lift until you reach .050″ below it and stop. [You are taking readings on both sides of the cam lobe.] Read the wheel and note the number of degrees. Take these numbers (example, 1st reading, 62 degrees; second, 150 degrees ) and add them (62+150=212). Divide this number in half (212/2=106) and you will have confirmed the intake centerline (106). [Additional note: Go through this procedure twice to verify your numbers. Accuracy takes practice. For additional information on degreeing cams, consult the cam manufacture’s degreeing instructions.]