Capital gains exclusion 2 year rule

[Ben Pohle]

if I were to purchase a property as a primary residence, reside in it for 2 years, then rent it out for 2 additional years and sell it at the end... 

Will I still be exempt from capital gains up to $250k single/$500k joint filer, or does that get "wiped out" after it became a "business?"

Assuming no other exclusions from capital gains within that time frame.