Smoke from breathers.

As far as the leakdown test, it would take a lot of typing to try and explain all technical stuff. So if you have plenty of time on your hands to read through this, lol, i'll post the link to article in CC.

http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/viewall.html

A comp test or even just pressuizing a cylinder can show a obvious failure. If neither shows a problem, a leakdown would be the next test to evaluate the condition of the engine.