depends on what ur planning on doing, normally u replace the water pump, timing belt, alternator belt, while the engine is out and might as well do a new exhaust manifold gasket if ur old one is shot if u never took it off then ur good to go, if everything is decent then just slap it in there and call it a day, when i put in my last engine i did everything b4 i dropped it in just because i didnt want to take it out and had the down time to play around