WARNING: This page is about a different car, the 2016 BMW Z4, 2015 BMW Z4, and 2014 BMW Z4. However, it is still accessible from the selected car via links, so may be relevant.
TIGHTENING TORQUE SPECIFICATIONS - STARTER MOTOR WITH MOUNTING
Type
Thread
Tightening specifications
Dimension
1AZ Starter motor to crankcase/transmission housing