It is incomplete to even talk about degreeing a camshaft without discussing piston-to-valve clearance. It's like learning how to drive but never being taught how to use the brakes. Learning how to make the car go is nice, but it's critical to understand how to make it stop! It's the same way here: Having the camshaft off by a degree or two never blew up an engine, but banging the valves into the piston top sure has.
The only way an engine will blow up after being degreed in wrong is if there is a lack of piston-to-valve clearance-the further you advance a camshaft the less intake valve-to-piston clearance you will have; conversely, the further you retard a camshaft the less exhaust valve-to-piston clearance you will have. I think you can see the importance of the relationship between degreeing a cam and the piston-to-valve clearance.
I know a lot of guys who are willing to trust the cam card and will plug in exactly the rocker-arm ratios the cam card tells them to. But as soon as you start playing with different combinations-which is what you are going to have to do if you hope to find a horsepower advantage-you are on your own. Don't ever assume you have enough piston-to-valve clearance unless you have plenty of money and are willing to learn the hard way. Hopefully, if you are that kind of guy, you are buying your pistons and valves from me. This also applies to anyone who thinks the process of checking piston-to-valve clearances is too time-consuming. Rebuilding your engine because you have needlessly bent all the valves is what is really time-consuming.
Mock-up Engine So what is involved in checking piston-to-valve clearances with the degree wheel? Glad you asked. It's really not all that difficult. One note: Although checking piston-to-valve clearances isn't tough, there are several steps. Probably the easiest way to get the gist of how we do this is to take this copy of Circle Track to your shop and try each step on an engine as you read along.
Once you have all your parts ready to assemble your engine, it is time to mock-up your short block. Set your crank, cam, timing chain (or belt), and your No. 1 piston and rod assembly in the engine. Don't be afraid to put the top ring on the piston for stability, and attach the cap on the end of the rod with fasteners for safety. Although this is a mock up, we still need to lubricate the parts as if it is the final assembly. At this point I like to put my degree wheel on and use a dead stop to find my TDC (top dead center) mark.
With your degree wheel in place, go ahead and set your cylinder head on the engine and fasten it securely with a couple of fasteners. Your cylinder head should have the intake and exhaust valve in place for the cylinder we are checking. I also like to install valve seals to ensure the valves will not fall out. At this point using the head gasket is optional; but if you decide not to use one remember that you must add the compressed thickness of the head gasket to your final piston-to-valve clearance figure to be accurate.
Now that your cylinder head is securely fastened to the engine block, it is time to set up your dial indicator to indicate valve travel.
We will be checking our piston-to-valve clearance for the intake valve at TDC and 10 degrees ATDC (after top dead center), and the exhaust valve at TDC and 10 degrees BTDC (before top dead center). The locations are where the piston and valves will be the closest through the cycle.
With your dial indicator on the exhaust valve, turn the degree wheel clockwise to 10 BTDC, making sure the valve is securely closed and your dial indicator is at zero. Next, slowly move the exhaust valve down toward the piston while you are watching the reading on your dial indicator. Once the valve is firmly against the piston and will not move down any farther, write the reading from the dial indicator on a piece of paper. This is your valve drop for the exhaust valve.