Here's the Cliff's Notes version of doing a compression test:
1. Make sure all the valves are closing- - - -precise adjustment isn't a concern right now- - - -just be sure there's at least SOME clearance when each valve is closed.
2. Remove all the spark plugs. Block the gas pedal wide open and make sure the choke is fully released.
3. Disable the ignition. On a pedal start truck just leave the key in the "off" position.. Disconnecting the primary wire at the side of the distributor is a foolproof method regardless of how the coil is wired.
4. Spin the engine with the starter after connecting the compression gauge to the #1 cylinder. Let the compression "hit" 3-4 times. Record the reading and move on to the next cylinder.
5. Repeat step #4 until you run out of cylinders.
6. If the compression readings aren't within about 5% of each other, squirt a couple of tablespoons of motor oil into the cylinders one at a time and repeat the sequence for a "wet" compression test. This temporarily seals worn piston rings. Little, or no pressure increase will be seen in a cylinder with a bent, stuck, or burned valve on a wet test.
Two adjacent cylinders with low or no compression pressure probably indicates there's a head gasket blown out between those cylinders.
Good luck!
Jerry
