Taking a few minutes to degree in your camshaft will ensure that it is optimized to do its
Stock car racing engines are all about precision. We're talking about a level of attention to detail that most people would consider obsessive. For example, if you've spent much time around musclecar guys or street rodders, you may have heard a few bragging about having their engine blueprinted. But I bet you've never heard an experienced racer brag about the same thing.
That's because any racer or engine builder worth his salt will consider blueprinting part of the standard operating procedure when it comes to race engines. Blueprinting is simply a fancy way of saying that every critical measurement on every part is matched to the engineering blueprint, and allowable tolerances have been held to the absolute minimums. On road cars, blueprinting is a luxury, but because of the stresses involved, a race engine that hasn't been blueprinted is a repair bill waiting to happen.
After installing the cam, install your timing set.
An important part of the blueprinting process is degreeing the camshaft. This is necessary to make sure the cam's timing events are properly synched with the crankshaft's position. There are a couple of reasons for doing this. The first is to make sure your cam timing is actually correct. The most obvious reason for the timing to be off is an improperly ground cam, but this is actually very rare. More common reasons are: a poorly machined block and/or heads; the cam or crank gear is incorrectly marked; a condition exists with incorrectly machined cam- or crank-gear keyways; or there is simply an accumulation of incorrect machine tolerances. Second, by manipulating the cam's position relative to the crank's, you can influence where in the rpm range the engine will make power. For the majority of engines, advancing the cam (moving the point of maximum intake lift closer to piston TDC) will move the peak power lower in the rpm range. Going in the other direction will do the opposite.
The most reliable and simplest method for degreeing in a cam is the Intake Centerline Method. This method does not involve a lot of complex calculations or require a lot of expensive equipment, but degreeing any cam does require a few specialized tools. You can assemble the tools yourself, but in many cases it's easier to purchase a kit from an engine parts supplier. We are using a camshaft degreeing kit from Powerhouse Products that gathers everything into a convenient case. This way, everything we need is in one place when we need to degree a cam on an engine and we won't have to go scrounging all over the shop. Powerhouse offers specialized kits for degreeing a cam with the cylinder heads either on or off the engine. We chose the heads-on option because it is simple, and whenever you perform a cam swap on an existing engine it allows you to check the cam without having to pull the heads.
This is the positive piston stop. It installs in the spark-plug hole and extends into the
PreparationThe first step is to make sure your camshaft and timing set are properly installed. Begin by installing the timing set "straight up," neither advanced nor retarded. The tick marks on both the cam gear and crank gear should be pointed directly at each other (the cam-gear mark pointing straight down and the crank-gear mark pointing straight up). If you have all of your valvetrain assembled, that's fine. We don't because we prefer to degree in the cam during the pre-fitting process. This is recommended because if you catch a problem you're still early enough in the build to fix it without causing a crisis.
You'll also notice in the photos we're using an adjustable-length checking pushrod. We are also using the lightweight checking springs included in the kit from Powerhouse. If you choose to check the cam during the pre-fitting stages, just install one of the rocker arms you plan to run on the intake valve on the No. 1 cylinder (it's the second valve back on the right side of the engine) and use a checking pushrod at the proper length to set the valve to zero lash. Finally, you should also have your cam card handy to check against the manufacturer's specs.
The Powerhouse kit we are using allows you to degree the cam with the heads attached to th
Finding Piston TDCInstall the included degree wheel on the nose of the crank and use the piece of wire to form a pointer. You can mount the degree wheel by using the crank bolt, although this isn't the best idea since you'll need to turn the crank both clockwise and counterclockwise, and the bolt can loosen and allow the wheel to spin. It also can be bolted directly to the harmonic balancer, but the best idea by far is to use a crank socket from Comp Cams. The socket not only allows you to spin the crank in both directions, but it also provides the best method of securing the wheel to the crank. Next, secure the included wire to the block and bend it to form a pointer as close as possible to the wheel without touching it.
Now, remove the rocker arms and install the included piston stop into the spark-plug hole for the No. 1 cylinder. If you don't remove the rocker arms, you could cause a false reading if the pistons hit the top of the positive stop. Using a half-inch ratchet in the crank socket, slowly turn the crank until the top of the piston contacts the stop. Spin the degree wheel to make this the zero point on your pointer and tighten the wheel back down. Now turn the crank the opposite direction until the piston contacts the stop again, and mark that point on the wheel. Remove the positive stop from the spark-plug hole. Divide the number by 2-this is piston TDC. For example, on our engine the point was 52 degrees. That means piston TDC is at the 26-degree mark. Spin the crank until the pointer is at your TDC mark. Now, without moving the crank, loosen the wheel and spin it until the zero mark is underneath the pointer. Now you know that piston TDC for your checking cylinder is at zero degrees on the degree wheel.
Go ahead and reinstall the rocker arms, setting the lash to zero.
Measure Valve MovementFinally, the fun can begin in earnest. Mount the dial indicator on the head and position it so it touches the outside edge of the intake-valve retainer opposite the rocker. Make sure the indicator is parallel to the valve stem. If it isn't, your measurements won't be correct.
Rotate the crankshaft clockwise until you reach the valve's maximum lift. You'll know because the pointer on the indicator will start moving back in the other direction. With the valve at max lift, set the dial indicator to zero.
Rotate the engine counterclockwise until the indicator reads 0.100 inch. Spinning the crank clockwise again, turn the engine until the dial reads 0.050. You always want to hit your points by spinning the crank in the same direction it will rotate when the engine is running. This will remove variances created by slack in the timing chain. If your rings provide a lot of friction, it can be easy to go too far. If so, back up and try again. Just do not set the dial to 0.050 by turning the crank counterclockwise.
Once you have the indicator on 0.050, record the degree-wheel reading. Continue to rotate the wheel until the indicator goes to 0.050 on the other side of maximum lift. Record the number the indicator is pointing to on the wheel again.
You can find your point of maximum lift in terms of crank degrees by taking the two numbers and averaging them. In our example, we came up with 80 and 140 degrees on the wheel. The average is 110 degrees, which means the intake valve for the No. 1 cylinder achieves maximum lift 110 crank degrees after the piston has reached top dead center. It is also exactly where our cam card tells us it should be, so we can continue assembling our engine with confidence that the cam is set for optimum performance.
Install the degree wheel on the engine. We're using a crank socket from Comp Cams that all
Install the dial indicator on the head so it touches the outside edge of the valve retaine
Several options are available if you want to advance or retard the cam timing.