Degreeing The CamshaftsCamshaft manufacturers make their cams to a certain reference point so when installed correctly they perform to their design specifications. When installing cams it might seem that just setting your fancy adjustable cam gears to zero means the cams are installed correctly. What if the cam gears are a little bit off in their manufacturing or the dowel pinhole is off a few degrees? How about if the head was shaved and now the cams sit closer to the crank? Any of these variables will affect cam timing and what you thought was zero is now something different. Every proper race engine should have the cams degreed. This doesn't mean retarding and advancing the camshafts until you make more power. It's a process where measurements are taken to ensure the camshaft is installed per the manufacturer's specifications-basically to start from a zero point. Since I'll be testing so many camshafts I need to degree each camshaft to make sure that I'm running them like the manufacturer intended. This process requires a few tools and some patience. You need a degree wheel so you can see how many degrees the crank is turning and a dial indicator to measure the amount of valve lift. I assembled a used "test" engine on a stand for the measuring process. Stiff factory springs can make testing difficult, as the spring force will try to spin the cam around on the opening and closing ramps. To make things easier, I swapped in some light springs.
Every manufacturer will give you some specification on how the cams should be installed. For this example we'll use a cam card provided by Crane Cams. Cam cards give valve lift points in reference to top dead center and bottom dead center. Before we begin we must first find top dead center, where the piston is at its top most position. Using a degree wheel, we mount the device to the crank snout. In our case we're using a digital degree wheel from Altronics. This new device replaces the traditional degree wheel and pointer system.
This method offers some major advantages over the old technique. Screwing in a piston stop into the spark plug hole on cylinder No. 1, we rotate the engine one way until the piston makes contact on its way to top dead center.
A push of a button and then spinning the crank the other way until it hits the piston stop and the Altronics Digicam computes top dead center. This system is much more accurate and quicker than the traditional degree wheel. Next, we mount a dial indicator in a way that we can accurately measure valve lift.
While this sounds easy, it requires some thinking and possibly fabricating some fixtures to hold the dial indicator correctly and securely. As with most engine applications, the 4G63 engine uses hydraulic lifters, meaning oil pressure is constantly adjusting valve lash. Unfortunately, with no oil pressure these lifters start to collapse if you push down on them. In my test, where there was no oil pressure, the cam lobe would ride on the follower and collapse the lifter instead of transferring all of its motion to the valve. Solid lifters to the rescue! Installing these and then adjusting the lifter until there is a little preload ensures that the cam lobe motion will be transmitted to the valve motion.
With our dial indicator installed, we've found top dead center and the cam is ready to be degreed. The Crane Cams card specifies that the intake valve should open 0.050 of an inch at 4.5 degrees before top dead center. We spin the crank over until the Digicam reads 4.5 degrees before top dead center. We look at the dial indicator and see that we're at 0.060 of an inch of lift, which is 0.010 of an inch more than specified on the cam card. The valve is open too far at this point so the solution is to loosen the cam gears and retard the cam until lift comes back down to 0.050 of an inch. Looking at the cam gear, the timing marks indicate the cam is now 2 degrees retarded.