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Originally posted by FoxBodyNick
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To use the clay method take a 1/4th inch amount, cover the valve reliefs on your piston and rotate the engine one full cycle. Make sure it's 2 revolutions past top dead center. Take the head back off and peel the clay away. The best benefit of clay is that you can use an x-acto knife and cut it into sections and measure exactly where the thinnest area is, if there is any. Remember .080 and .100 minimum thickness.
The next method takes a little practice but is great if you dont want to take the heads off the car, although it will be necessary to replace the intake and exhaust valve springs on one of the cylinders. I use a checkign spring, but if you don't have a dedicated light weight spring, take a trip to your local hardware store. Remember the spring only has to have enough pressure to keep the valves fully closed and return an open valve back to it's closed postition.
Ok let's jump forward, you have replaced the intake and exhaust valve springs with lightweight springs. Now you want to adjust the rockers to zero lash. What is important here is if you are using a hydraulic type cam, wether it be a hydraulic roller or flat tappet hydraulic cam. Do NOT preload the lifter. All you want to do is take all the movement out of the pushrod WITHOUT collapsing the plunger in the lifter. Make sure you do this adjustment when the lifter is on the base circle of the cam which is at top dead center on the compression stroke.
So now we have the valves ready for measuring. You will need feeler gauges set to 0.100 thousandth's. Start with your piston at top dead center and rotate one full revolution in normal operating rotation. Keep your eyes open now, as the piston starts traveling back up the bore the exhaust stroke starts to occur and the exhaust valve will start opening. Watching the valve train you will notice the exhaust valve opening till it's fully open. As you are approaching top dead center you will notice the intake valve starting to open before the exhaust valve is fully closed. This is the area of overlap, usually about 10-15 degress before and after top dead center. Both the intake and exhaust valves are open and the piston is near the top.
During this overlap point is when you want to measure the piston to valve clearance. The piston is so close to to the top that you can push down on the nose of the rocker and actually feel the valve making contact with the piston. Now with your feeler gauge set to 0.100 insert the feeler gauge between the valve stem tip and the rocker arm. If you can insert the gauge at 0.80 for the intake and 0.100 for the exhaust then you have enough piston to valve clearance.
It may take you some trial and error before you can identify the prescise overlap period at which you need to check the clearances, but this is a good way for someone that does not want to take off the heads.
I highly suggest you go through the steps above several times, it is VERY easy to miss the overlap, resulting in very unaccurate measurements. Work slow and this process can be accomplished by just about anyone.
Final note, if your measurements are say less than 0.10, for example there is .090 clearance on the intake you can retard the camshaft and play around with that but remember that will also affect performace charactersitics of the cam. Hope this helps. lol.
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