To start work on Z4 vehicles, you need to disconnect the cable(s) attached to each battery negative terminal. Next, remove the air filter housing. First write down where the starter elements are originally connected. Then, unscrew the nuts holding those parts and disconnect the wiring coming from and going to the starter motor. First, remove the mounting bolts from the starter that connects the engine and transmission. Raise the starter from its place in the engine bay. When putting things back in place, follow the steps you used to take them out. Make sure to tighten all fasteners according to the recommended torque values.