If you are wanting to replace a used engine there are a few things to keep in mind. 1st decide if your going to keep your transmission or get a used transmission to install as an assembly with the used engine(front wheel drive cars the assembly has to come out from under vehicle).

Disconnect the battery, drain fluids from radiator, and remove radiator. If pulling transmission block wheels pull driveshaft and plug the tail of the transmission to keep fluid from spilling. Then remove distributor cap (if equipped), unbolt exhaust (depending on car may be easiest to remove exhaust manifolds from engine, some cars it's easier to unbolt them from the exhaust pipe). Remove the starter and alternator. Attach engine hoist. If leaving transmission in car unbolt from engine, be careful as it may drop, use a jack to support.If pulling transmission disconnect shifter linkage, cooler lines (if equiped)any electrical connections, and speedometer cable (if equiped).remove and label all electrical connections on engine. If engine has a turbocharger disconnect it to avoid damage. Double check that no wires or cables are still attached to engine, and remove motor mount bolts (make sure there is tension on hoist or it will drop). Use hoist to slowly lift engine from car making sure to keep assembly clear of hitting any body part.You may need to tilt engine to clear firewall or other body part.

Now is a great time to clean that road grime from the engine compartment, and do some painting.While apart check the motor mounts for wear.On the used engine you should replace wear items such as water pump, timing belt, spark plugs, and wires.Installation is reverse of removal, just go slow and line everything up. Before starting engine make sure and change the oil.If the transmission was left in the car make sure the fluid is full before starting engine also.