Overview Degreeing a cam
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Overview Degreeing a cam is a method to check that the actual valve timing events of the camshaft match the specifications on the cam card. While the odds of a cam being manufactured incorrectly are slim with today's production standards, the process of degreeing accounts for other variances such as a misindexed crank keyway or timing gears.Consider that your timing gear set could be off one degree, and that the crank keyway is one degree, so on and so forth. All these seemingly minor factors can significantly change the specs on your cam. Degreeing a cam is simple and easy to do. All that is required is a degree wheel, piston stop, and a dial indicator with magnetic base. You don't need to spend a lot on these parts and they will be invaluable for future engine projects or cam installations.Degreeing can be achieved with the heads installed or removed from the block. If the heads are installed, you will need a spark-plug hole type piston stop. If the heads are off the car you can use a stop that mounts on the block itself. Before diving into the degreeing process you should be familiar with how to read and interpret a dial indicator, degree wheel, and the manufacturer's cam specifications.
Reading a Dial IndicatorMost indicators have a total of 1" travel before the plunger bottoms out. One revolution of the large pointer is 0.100", and each small hash is .001". The small dial on the face records the number of revolutions in hundred-thousandths (0.100") up to ten revolutions, (one inch). The outer bezel rotates so you can set to zero. Reading a Degree Wheel
Good degree wheels will split the wheel into quarters, and label Before and After Top Dead Center (TDC), as well as Before and After Bottom Dead Center (BDC) If yours doesn't show these sections (see image), don't worry, you can mark them yourself. Reading a degree wheel is common sense. A circle has 360°. In a fourstroke engine, each stroke (movement of crank up or down the bore) is therefore 90° of crank movement. Camcards indicate valve opening and closing events based on whether they occur before or after the piston at the top or bottom of the stroke. Reading the Cam CardThe cam card is provided by the camshaft manufacturer and lists all the
specifications for that particular cam. Without this card you can still degree the cam but you won't know if the results are correct. A typical cam card or sheet shows the intake and exhaust lobe ("tappet") lift, the duration in degrees the valve is open, measured at 0.050" valve lift. The cam card also shows the timing events, i.e. when each valve opens and closes. The degreeing process will verify all of these specifications.Follow along as we outline the steps involved in degreeing a camshaft. Note that we are assuming the camshaft has been installed with the timing gears set to "straight up" (no advance or retard applied via the crank gear.) Install the degree wheelBring the number one piston to the top of its bore and securely mount the degree wheel to the crank snout and set up a sturdy pointer. We simply bent some pipe strapping and bolted it to the block. Line up the pointer with the Top Dead Center mark on the wheel. We'll verify true top dead center in the next step. Find true Top Dead Center Install the piston-stop on piston #1. We rigged up a stop using a pushrod guide plate and some bolts. Rotate the engine clockwise until the piston contacts the stop. Mark the degree wheel at this point. Then rotate then crank counterclockwise and mark the degree wheel again.
Adust the degree wheelExact TDC is halfway between the two marks you made in step 2. If in step 2 you counted 20 degrees to one side of the TDC mark and 24 degrees on the other, you would move the degree wheel two degrees, so that you have 22 degrees on each side of the TDC mark. Perform step 2 again until you come up with the same degrees on either side of the TDC mark. Once you set final adjustment to the degree wheel, do not move the wheel or pointer throughout the degreeing process. Verifying gross liftMount the dial indicator plunger on the lifter edge as shown. Set the piston to TDC and zero the indicator. (If you are degreeing with the heads on, then place the plunger on the tip of the pushrod.) Rotate the crank in the normal direction of engine rotation (clockwise). Note the total lift on the dial indicator. The total lift should be within .003" of the value on the cam card. Repeat this until you can obtain consistent readings for both intake and exhaust lifters.
Verifying valve open pointBring the piston to TDC and set the dial indicator to zero on the intake lifter. Rotate the crank clockwise until the dial indicator shows exactly 0.050" of lift. Stop rotating and read the degree wheel and compare it to the cam card specification for "Intake Opens" at 0.050" lift. Verifying valve close pointContinue to rotate the crank until the valve reaches 0.050" from fully closed. To do this, watch the dial indicator as you slowly rotate the crank. When the intake valve is fully open the dial indicator will be at the gross lift as specified on the cam card. As the valve starts to close the needle on the indicator will move backwards. Stop when the needle is 0.050" away from zero. Take the reading and compare it to the cam card specification for "Intake Closes" at 0.050" lift. Set the dial indicator on the exhaust lifter and Repeat steps 5 and 6 to obtain exhaust readings.
ResultsIf your opening and closing figures are more than 2 degrees off, you will need to move the cam in relation to the crankshaft in order to correct your opening and closing figures. If the cam is opening early, the cam is too far advanced, and will need to be moved in the opposite direction of the crank rotation. If the cam is opening late, the cam is too far retarded, and will need to be moved in the direction of crank rotation. Depending on the engine being used, there are usually offset bushings, offset keys, or multi-indexed gears to accomplish this movement. If the lift numbers are off more than 0.003", you should contact the cam manufacturer as the cam may have been ground incorrectly