No idea how to do a leak down test but I willing to give it a shot.
If you are a newbe, and you do not have a LD tester;
here's what I recommend.
1) Take off the driver's side VC, and look for a sloppy pushrod preload, on the low-pressure cylinder, as compared to another cylinder with good pressure; which may signal a cam-lobe going down. Of course the checking has to be done with the lifters on the base-circles. If you suspect a loose fit, more testing is needed.
As to the LD test
2) Next, remove the radcap, and fill the rad right up. Cuz;
Later, as you put pressure to the cylinder for this type of LD test, the piston will fly to the bottom; and the chamber will pressure-up. Keep your knuckles away from the fan! Then; Right away, check the coolant in the rad for bubbling. As the pressure comes up, 100psi can do damage in the rad if the headgasket is leaking; So if you get bubbling, or the water blows out; stop the test!
If no bubbling, then for the rest of the time, keep one eye on the filler-neck.
3) Next, remove the rocker gear. This will allow the cylinder to seal up, as good as it can get. What you need to do now is to inject air into the plug-hole, and see where it comes out.
But
If you hear air coming out the carb, or air coming out the tailpipe, then, one or both of the valves are leaking. Since the piston is at the bottom, you can now bop the valves without fear of bending them on the pistons. I smack them with a dead-blow hammer, but you can use whatever. Don't go crazy cuz it is possible to kick a lock out.
After every bop, listen for a change or decrease in the hissing, and/or a change in the sound of the valves smacking back onto the seats. As you continue, if you get a sharp "pop", and the hissing more or less quits then stop the test. What you are doing is smashing the carbon off the seat, and simultaneously blowing it out.
If this works, then after a few bops, any hissing left is going into the CC past the rings, which is sortof normal.
But if the hissing never stops
You may have a bent or burned valve.
5) Put the valve gear back on, with the rocker shaft oriented correctly, and correctly torqued to IIRC 15 ftlbs for 5/16ths bolts. Then
6) redo the compression test.
If the numbers are same as before, you still don't know if it's bad or stuck rings, or a scratch in the cylinder wall, or really could still just be valves; so now, you gotta go rent an LD tester, and repeat the test with the Piston at TDC/Compression, minus the valve bopping..
