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Dialing in a cam


Blair

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Fuck it.

Set up the DTI over number one piston with the head off. Wind the crank over untill the piston reaches the top of it's stroke. (When the DTI needle stops moving, but no further) note where the degree wheel is. (Mark it if need be) Wind the crankshaft in the other direction untill the piston reaches the top of it's stroke again. Make a mark. The point in the middle of these two marks is true TDC. This is because there will be a few degrees of dwell at tdc. Place a pushrod in the inlet hole for number one. Place the dti above it so that the pushrod is as vertical as possible. This will allow the DTI to measure the cam lift as acurately as possible.

Wind the camshaft around untill the dti shows .050 of lift.

Check the cam spec sheet. It will say something like cam timing at .050,

inlet opens @ 7.5' BTDC . (Or something) Starting from your true TDC, wind the crankshaft forward (or back) the desired number of degrees. then assemble the timing chain etc. You really need an adjustable cam gear. (Kelfords sell these) Or you set up your cam sprocket half a turn out, and drill a new dowel hole into the end of the cam. (on an A series Datsun motor)

Once you've tighened up your adjustable gear, (If you bought one) wind the motor over clockwise and check the number of degrees on the degree wheel when the DTI reads .050 as the valve is closing. This should match the Valve closing timing on the cam specs. Then to be extra sure it's right, check the opening and closing timing on the exhaust valve too.

If you run your cam a wee bit advanced, (Have the valve open @.050 before the number of degrees in the cam specs) The engines powerband will be slightly lower in the rev range. And if you run it slightly retarded, the powerband will be later in the rev range. As a motor wears the cam timing will become slightly retarded and a used motor will begin to feel like it revs a bit more freely.

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Thanks Bart.

Here's What I have found so far............ Dont you just love copy n paste!!!

The Procedure to Degree the Camshaft

1. The dial indicator and stand must be attached securely to the engine. Any deflection could cause an error in your readings. Using the number one cylinder as a starting point, hand rotate the engine in a normal direction (clockwise, when standing in front of the engine) until the intake valve is closed (the lifter is down on the base circle of the cam lobe). If the intake manifold is off the engine, mount the plunger of the indicator directly on top of the intake lifter itself.

If the intake manifold is on the engine, you can use the pushrod as an extension to the dial indicator and mount the plunger tip directly on top of the pushrod. In either case it is important to make sure the angle of the dial indicator plunger is the same angle as the lifter or pushrod travel. We want to read "straight line" (linear) movement of these parts, so the plunger must be aligned properly. With the indicator in position, set the dial indicator to zero.

2. Hand rotate the engine in its normal direction of rotation while watching the dial indicator. As the lifter starts to move up the opening side of the lobe, the reading on the dial indicator will start to increase. Continue rotating the engine until the dial indicator shows .050" of rise. Stop and take a reading on the degree wheel and write it down.

3. As you continue to rotate the engine, the reading on the dial indicator will rise up to the maximum lobe lift. The lifter is now on the top of the lobe. (The maximum lobe lift is shown on the spec card and can be verified at this point if you wish.) Continue the rotation and the lifter will start down the closing side of the lobe. Carefully watch the dial indicator as the numbers descend. When the indicator descends back to the .050" reading, stop, take a reading from the degree wheel and write it down. Rotate the engine and return to the base circle of the lobe. The dial indicator must read zero again to be sure the process was correctly done.

4. You now have the two important readings from the degree wheel, both taken when the dial indicator read .050". One reading as the indicator was ascending on the opening side, the other when it was descending on the closing side. Compare these numbers to those on your camshaft inspection card to verify the position of the intake lobe.

The camshaft specification card provides much information, but the numbers you are most interested in for the degreeing of the cam are at the bottom of the card. In the box identified as "Cam timing at .050" Tappet Lift". (Just a reminder, the word tappet and lifter mean the same thing. This can also be expressed as .050" lifter rise.)

Inside this box are the degree readings that the degree wheel would show for the intake "opening" side of the lobe and the intake "closing" side of the lobe when the dial indicator is at .050" of lift. (Below those figures are the opening and closing figures for the exhaust.) Compare your readings for the intake to those on the card. If you're within a degree, your camshaft is installed in the correct position.

5. You can follow exactly the same procedure on the exhaust lobe to determine its opening and closing degree points at .050" of tappet (or lifter) rise, and compare these readings to those on the specification card. If you also check the exhaust lobe you will have four points of reference (intake opening and closing, and the exhaust opening and closing) to go by. Remember, if you are plus or minus one degree of these readings, your cam is in the correct location and will be synchronized to the crankshaft's rotation.

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