COMP Cams® Top 10 Tech FAQs

jjamros · #1 (**permalink**) 05-14-2010, 04:08 PM

From measuring pushrods to degreeing camshafts, read on to find answers to the ten most frequently asked questions that COMP Cams® Technicians receive.

1. How do I set valves for hydraulic and solid lifters?

Adjusting intake valves:

We recommend you work with one cylinder at a time. Using the crankshaft dampener bolt in the snout of the crankshaft, turn the engine over by hand in the direction of its running rotation until the exhaust pushrod just begins to move upward to open the valve. Stop rotation. The intake lifter is now on the base circle of the cam, and the intake valve is ready to be adjusted.

Hydraulic Lifter Cams:

Tighten the polylock until all the slack is taken out of the rocker arm and pushrod. By lightly turning the pushrod with your fingers as you tighten the polylock, you will discover or feel a point at which there will be slight resistance. At this point, you have taken all the excess slack out of the pushrod. You are now at what we refer to as “zero lash.” Turn the polylock 1/2 turn more, and while holding it with a wrench, tighten the set screw using a T-handle or Allen wrench. This will give you the ideal preload of the rocker arm, pushrod and lifter. Repeat this procedure for each cylinder and carefully adjust all intake valves.

Solid Lifter Cams:

Consult cam spec card or cam manufacturer for correct lash specifications. With the proper feeler gauge between the roller and valve stem, turn the polylock until a slight drag is felt on the feeler gauge. Hold the polylock with the wrench, and then tighten the set screw using a T-handle or Allen wrench. Repeat this procedure for each cylinder and carefully adjust all intake valves.

Adjusting exhaust valve:

To adjust exhaust valves, turn the engine over until the intake pushrod moves all the way up. Rotate past maximum lift, approximately 1/2 to 2/3 of the way back down. The exhaust lifter is now on the base circle and the exhaust valve can be adjusted.

Hydraulic Lifter Cam:

Rotate the exhaust pushrod with your fingers and begin to
tighten the exhaust polylock. When you feel resistance on the pushrod, you are at “zero lash.” Rotate the polylock 1/2 turn more, and then tighten the set screw. Go through the exhaust valves, and repeat the procedure carefully. Now all of the valves are adjusted with the proper preload.

Solid lifter Cam:

Tighten the polylock, with the proper feeler gauge between the roller tip and valve, to the point at which there is a slight drag when moving the feeler gauge. Hold the polylock with the wrench and tighten set screw. Following this procedure, carefully adjust all exhaust valves.

2. How much preload should I look for in a typical hydraulic Lifter?

You should look for .030-.060 of preload.

3. How do you figure out what your lift will be with a different rocker ratio?

You take the lobe lift given on the card and multiply it by the rocker ratio (e.g.,.400 x 1.6 = .640). Or you can divide the valve lift given on the card by the rocker ratio it is given with, and then multiply it by the new rocker ratio.

4. What is the difference between different Lobe separations?

Tighter lobe separation tends to narrow the power band and typically increase the peaks. Tighter separation will also increase cylinder pressure and increase bottom end torque. Narrow also reduces piston to valve clearance, hence too narrow creates many issues with fitment. Also, narrow will decrease engine vacuum at idle and may cause issues with misfire. And, wider lobe separation will do the opposite of the points on tighter separation.

Lobe Separation = (Intake Centerline + Exhaust Centerline)/2

5. What is the difference between different Intake Centerlines and how is this not the same as lobe separation?

By advancing and retarding a cam, you can move the ICL wherever you would like, but unless you have separate cams for the intake and exhaust (like the DOHC Ford) you cannot change the lobe separation once a cam is ground. Advancing the cam will make more cylinder pressure and build bottom end while retarding will broaden the power band and add top end, but can also make the motor a little lazier on the bottom.

6. How do you determine pushrod length with a checking tool?

Technique #1

This technique requires the use of a COMP Cams® Hi-Tech™ Pushrod Length Checker. These are marked with a standard length stamped in them. This number represents the gauge length of the part (.140" gauge diameter), with the two halves screwed completely together. Extending the pushrod one rotation lengthens the gauge length .050". For example, a pushrod stamped 7.800 and screwed apart one rotation would be 7.800" + .050" = 7.850" gauge length. Therefore, you would order the part number from the catalog that matches this gauge length, since gauge length is how they are listed.

Technique #2

This technique requires one of our Magnum Pushrod Length Checkers. Once fixed, you don’t need to have an expensive gauge or a pair of calipers to measure it. You just need a pushrod of a known length to compare it to (a standard). Then use a pair of common 6" calipers to measure the difference between the standard and yours.

Here are a few final tips for pushrods in general. It is always a good idea to buy a few spares when purchasing a set of custom length pushrods, and stick them in your toolbox. If one ever fails at the track, and you need a replacement, it would be nearly impossible to borrow one from a fellow racer.

Another hint involves cup end pushrods. Measuring them for length is especially difficult, no matter which technique above you choose to use. The size and shape of the cup end varies greatly from manufacturer to manufacturer, so measuring from the ball end to the cup end over the cup surface is a dangerous practice. The best strategy is to drop a 5/16" diameter steel ball into the cup end, and do all measuring over this ball, subtracting the 5/16" diameter (.3125") to calculate the length.

7. How do you check piston to valve clearance?

Step 1:
With the camshaft installed, remove the cylinder head from the block. Clean the combustion chamber and the top of the piston and valve reliefs. The cleaner the piston, the better the clay will stick to it.

Step 2:

Apply a strip of model clay 3/8” to 1/2” wide and approximately 1/4” thick to the pistons. The clay strips should be placed perpendicular (across) to the intake and exhaust valve reliefs (fig. 1). Applying a small amount of oil to the clay will prevent it from sticking to the valves as they press into the clay.

Step 3:
Reinstall the cylinder head with the gasket that is going to be used. It will not be necessary to re-torque the head yet. All head gasket manufacturers can tell you what the compressed thickness of their gasket will be. Measure the gasket before you install it permanently, and add the difference of the gasket thickness to your piston to valve clearance. This will be within .001” or .002” of the exact clearance. Install a sufficient number of head bolts to secure the head in place while you are rotating the engine. Install the pushrods, lifters and rocker arms on the cylinder you have prepared for the clearance check.

Step 4:

Adjust the rocker arms to their suggested clearance. If the camshaft you are checking uses hydraulic lifters, you must temporarily use solid lifters in their place. Hydraulic lifters bleed down and would create a false measurement. Once the hydraulic lifters are replaced with solid lifters, adjust the lash to “zero.” Be sure not to pre-load the valve spring (fig. 2) (be sure to reinstall the hydraulic lifters before starting the engine).

Step 5:
Turn the engine over by hand in the normal direction of rotation. Be sure to rotate the engine over 2 times. This will be one complete revolution of the cam and, it will assure you of an accurate reading on both the intake and exhaust. Remove the cylinder head from the block. Be sure to do this gently, so the clay is not disturbed. It may be stuck to the valves or combustion chamber, so be careful.

Step 6:

With a razor or a sharp knife, slice the clay cleanly, lengthwise through the depression and peel half of it off the piston (fig. 3). The clay’s thickness in the thinnest area will represent the minimum piston to valve clearance.

Step 7:
To accurately check the thickness, use a set of dial calipers (fig. 4). The clay can also be measured close enough with a thin steel rule.

Note: Be sure to check piston to valve clearance after the cam has been degreed in. The positioning of the cam in the engine will greatly affect the piston to valve clearance.

8. How do I degree a camshaft, and why we do we use the Intake Centerline Method instead of valve timing events?

The Intake Centerline Method

There are several accepted ways to degree a camshaft. At COMP Cams®, we feel the Intake Centerline Method is the easiest and most accurate. This method of cam degreeing is very practical and indifferent to design characteristics. It simply involves positioning the center, or point of maximum lift, of the #1 intake lobe with Top Dead Center of the #1 piston.

The Intake Centerline Method still requires accuracy to be correct, but it is somewhat more forgiving. Once you have degreed a camshaft using this method, you will be surprised at its ease. We also recommend positioning the dial indicator on the #1 intake retainer because lift measurements will include any deflection that may occur in the pushrod and rocker arm. This makes the degreeing process as accurate as possible in relation to what actually goes on inside the engine. Before you proceed, you will need a Cam Degree Kit (Part #4796) from COMP Cams®.

Time to Go to Work

Step 1:
The camshaft and timing set have been installed. Make sure that the timing marks on both the cam gear and crank gear are aligned properly, per the cam installation instructions. Use chalk or similar marker to better define the marks.

Step 2:
For example, we have our cam card, and it suggests we install the cam on 106 degree intake centerline. Install all the rocker arms and pushrods in the engine as normal. On the #1 intake lobe, install the solid lifter in place of the hydraulic lifter. If a solid lifter or roller cam is being checked, use that respective lifter. Adjust the #1 intake lash to exactly zero. Do not pre-load the lifter. Next, adjust the #1 exhaust lash to zero. You should be able to turn both pushrods with your fingers easily.

Step 3:
Attach your COMP Cams® pointer (Part #4794) to the block. Many people will make a pointer out of some sort of rigid, yet manageable wire. A stiff coat hanger wire works well.

Step 4:
Attach the degree wheel to the balancer, and install the assembly on the crankshaft

There are several ways to attach the degree wheel to the crankshaft. In our example, the degree wheel is mounted to the balancer. The crank may be rotated from either the front or from the flywheel end. Obviously, if the engine is in the car, you must rotate from the front.
Remember, the greater the leverage, the smoother the crank rotation, thus more accuracy. NEVER use the starter to turn the engine while degreeing the cam.

Step 5:
Before installing the piston stop, rotate the crankshaft to get the #1 piston in approximate T.D.C. position, with both the intake and exhaust valves closed. This can be a rough guess, but it can save you from making a mistake later. Adjust your pointer to zero or T.D.C. on the degree wheel.

Step 6:
Turn the crankshaft opposite the engine rotation approximately 15-20 degrees. This will lower the position enough to allow the T.D.C. stop to be installed in the spark plug hole. Screw in the piston stop until it touches the piston. (fig. A). Continue to turn the engine in the same direction until the piston comes back up and touches the piston stop. Mark the degree wheel with a pen or pencil on the number the pointer is on (fig. B). Turn the engine in the other direction (same as engine rotation) until the piston comes back up and touches the piston stop. Make a mark on the number the pointer is on (fig. C).

Step 7:
Remove the piston stop after marking the two points on your degree wheel. Rotate the crankshaft to the midpoint of the two marks. This point is T.D.C. for cylinder #1. Without rotating the crankshaft, adjust the degree wheel to read 0 degrees at the pointer (fig. D). You are now ready to locate the intake lobe centerline relative to T.D.C. If you are not absolutely sure that your 0 degree mark is set at T.D.C., repeat this procedure. This step is critical to proper cam alignment.

Step 8:
Attach the dial indicator to the dial indicator mount. Position the dial indicator mount so the tip will contact the retainer of the #1 intake valve (fig. E). It is important that the indicator plunger be parallel to the valve stem. Any variance in the angle of the indicator will introduce geometric errors into the lift readings.

Step 9:
Rotate the engine, in the normal direction of crankshaft rotation, until you reach maximum lift. The dial indicator will change direction at the point of maximum lift. At this point, set the dial to zero (fig. F).

Step 10:
Back the engine up (usually counter-clockwise) until the indicator reads .100”. Turn the engine back in the normal direction of rotation until (usually clockwise) the dial indicator reads .050” before maximum lift. Record the degree wheel reading.

Step 11:
Continue to rotate the engine over in its normal direction of rotation until the indicator goes past zero to .050” on the closing side of maximum lift. Again, record the degree wheel reading.

Step 12:
Add the two numbers together and divide by 2. That number will be the location of maximum lift of the intake lobe in relation to the crank and piston. This is the intake centerline. For example: The first degree wheel reading was 96 degrees. The second reading was 116 degrees. These two numbers (96 +116) added together will be 212. Dividing 212 by 2 will equal 106. Your actual intake centerline is 106 degrees. Reference back to your cam spec card, and we see that the recommended intake centerline for your camshaft is 106 degrees. Everything is where it should be. In the event that your camshaft did not degree in as per manufacturer’s specs, it will be necessary to either advance (move ahead) or retard (move back) the cam to meet suggested intake centerline. Depending on the engine application, there are several different suggested methods for advancing or retarding the camshaft. One common method is by use of a crank gear with multiple keyways, each one being at a slightly different relationship to the gear teeth. A second method is to use off-set bushings that fit on the cam pin and in the cam gear. The off-set will advance or retard the cam depending on how the bushing is placed on the cam pin. Another method is by off-set keys that fit into the crank gear keyway. A more elaborate system uses an adjustable timing gear. Contact COMP Cams® or your local COMP Cams® dealer for the method best suited to your application.

Note: When degreeing a cam, remember to look at the degree wheel as a full 360 degrees, no matter how the degree wheel you’re using is marked. Many degree wheels are marked in 90 degree or 180 degree increments. On wheels that are marked in 90 degree increments, keep in mind that you must continue to count the number of degrees past 90 degrees. Be sure all readings are taken from Top Dead Center. Keep in mind that to advance the cam, you must lower the intake centerline. For example, if our cam has a lobe separation of 110 degrees, the cam is “straight up” when the intake centerline is 110 degrees. Moving the centerline to 106 degrees advances the can 4 degrees. If we change the centerline to 112 degrees, this would be 2 degrees retarded.

9. What is installed height on a head and how does it affect the spring pressure and lift ability?

Basically, it is the height from the bottom of the retainer to the base of the head where the spring sets. Springs have recommended installed heights, and shorting or raising that height will affect the given specs for the spring. Shorting it will add pressure and take away lift ability; raising does just the opposite.

10. How do you properly break in a camshaft and what oils and additives should you use?

Use high zinc oil (such as the COMP Cams® Break-In Oil) with our 159 additive. Vary the RPM of the motor between 2000-2500 RPM for about 25 minutes. Do NOT try to constantly start the motor if you can not get it to fire with a new cam in it.