Cylinder Block

This is the Cylinder Block (often called the Cylinder Barrel or Jug) of an internal combustion engine. 

The above picture is from a small air-cooled engine, likely a moped or a small motorcycle. 

Key Features Visible:

• The Cylinder Bore: The large hole in the center is where the piston moves up and down.

• Cooling Fins: The horizontal ridges on the outside are designed to increase surface area so that air blowing past can pull heat away from the engine.

• Timing Chain Tunnel: The rectangular opening to the left of the main bore is where the timing chain (or cam chain) runs up to the cylinder head. This confirms this is a 4-stroke engine block.

• Stud Holes: The four holes at the corners are for the long bolts (studs) that hold the cylinder head, block, and crankcase together.