Not to hijack but.....these are related questions.

I always here people say that a leak-down test is a better determination of what's going on inside an engine. I know how a compression test is done, have a gauge, and can do that myself.

What is involved with a leak-down test? What is the procedure? How much for tools?

How much could I expect to pay to have a leak-down done?

Since I don't wrench professionally anymore I just bought a leakdown tester at Harbor Freight for $40. Procedure can vary but what I do is pull all plugs, use a remote starter switch to bump the engine over while I hold a finger over the spark plug hole until I hear and feel the compression stroke. Then I put a long thin screwdriver in the cyld and rock the engine back and forth by hand until I can feel that the piston is at TDC. Otherwise the air will push the piston down. Now inject the air into the cyld following directions as some testers work differently. If leakage is excessive then listen at throttle body/carb, oil fill, exhaust to hear where the air is escaping. I've done lots of these tests on cars. I'd loosen the belt on a marine engine first (water pump). You can also use a fully degreed harmonic balancer but my way works good. I used to use the test as a back up if the compression test showed a problem. Leakdown will tell you if it's an intake valve, exhaust valve, rings or head gasket or crack.

Thanks for the info. It does sound a little more complicated than a compression test.

a compression will tell you if something is wrong
a leak down test will tell you whats wrong