Engine Block: Crankcase

The crankcase has a one-piece "open deck" design and is made entirely from AluSil. The cylinder walls are hardened using a specific procedure (exposure honing). Exposure honing involves treating the cylinders with a special "soft stripping". This removes the aluminum from the cylinder surface and the hard silicone particles remain.

Open Deck = Exposed cylinder coolant chamber 

Fig 1: Identifying Return Coolant Collection Area

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Identifying External Cylinder Bank Wall

Courtesy of BMW OF NORTH AMERICA, INC.