A leakdown tester doesn't need to be complicated, although the kit in the link is handy and inexpensive. I just use an adjustable air pressure regulator from Harbor Freight and a spark plug shell with an air hose quick connect nipple soldered into it. Adjust the regulator to 100 PSI on the built-in gauge with no air flowing, and plug the air hose onto the adapter screwed into the spark plug hole. If the pressurized cylinder holds 90 PSI, for instance, there's a 10% leakdown rate. A cylinder with good piston rings, valve seats, and a head gasket that's not leaking should hold pressure in the 90%+ range. Listen at the carburetor, tailpipe, or crankcase filler to determine where the leakage is. A leaky head gasket or a cracked cylinder head will cause bubbles in the radiator.
Jerry
