A cylinder leakdown test is done by putting air into a cylinder through a spark plug hole with a quick-connect air line fitting brazed into a spark plug shell. Get each cylinder to top dead center on the compression stroke, and lock the crankshaft by putting the transmission into high gear and setting the parking brake, or using vise grips on the flex plate of an automatic transmission car. Listen for air leaks at the intake and exhaust, indicating leaky valves, or at the crankcase filler, indicating ring leakage. Bubbles in the radiator show head gasket leaks and/or cylinder head cracks. If you've got an adjustable air pressure regulator, adjust it to 100 PSI with the air line blocked off, and the pressure with air going into the cylinder will show you the percentage of leakage- - - -85 PSI=15% leakdown rate, etc. A good cylinder will have less than 10% leakdown, and a really good one will be under 5% leakage.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!