The crank case is the housing for the crankshaft.The enclosure forms the largest cavity in the engine and is located below the cylinders.Crankcases have often been discrete parts, but more often they are integral with the cylinder bank(s), forming an engine block.
A crankcase often has an opening in the bottom to which an oil pan is attached with a gasketed bolted joint.
The metal case enclosing the crankshaft and associated parts in a reciprocating engine.
The metal housing that encloses the crankshaft, connecting rods, etc., in an internal-combustion engine, reciprocating pump, etc.
I would beg to differ with Alex the component in question seems to be way up to have scratches (caused by rough terrain )without causing damage to other items nearby - its seems like a case of of the oil seals going kaput - Aluminium parts do have textures like the one seen in the picture.