Marine propulsion device

A marine propulsion device comprising:

• an engine cover;
• an engine disposed within the engine cover;
• a drive shaft disposed below the engine and along a vertical plane;
• and
• a propeller shaft connected to the drive shaft in a power transmittable state;
• wherein
• the engine includes:
• a plurality of cylinders:
• a plurality of pistons configured to slide inside the plurality of cylinders on a one-to-one basis;
• a plurality of connecting rods coupled to the plurality of pistons on a one-to-one basis, the plurality of connecting rods configured to convert reciprocating motions of the pistons into a rotary motion;
• a crankshaft coupled to the plurality of connecting rods, the crankshaft connected to the drive shaft in a power transmittable state;
• and
• a crankcase accommodating a portion of the crankshaft, an upper portion of the crankshaft and a lower portion of the crankshaft protruding outwardly from the crankcase;
• the crankshaft includes:
• a plurality of coupling portions coupled to the plurality of connecting rods on a one-to-one basis;
• a first functional portion provided on the upper portion of the crankshaft protruding from the crankcase, the first functional portion arranged to drive a first functional component;
• and
• a second functional portion provided on the lower portion of the crankshaft protruding from the crankcase, the second functional portion arranged to drive a second functional component;
• the entire crankshaft has been processed by a first treatment to at least enhance a corrosion resistance thereof;
• at least an entire surface of the plurality of coupling portions of the crankshaft have been processed by a second treatment to at least enhance a strength thereof;
• and
• neither of the first functional portion and the second functional portion has been processed by the second treatment.

A method of manufacturing a crankshaft in a marine propulsion device, the method comprising the steps of:

• shaping a crankshaft to include a coupling portion configured to be coupled to a connecting rod, a first functional portion provided on an upper portion of the crankshaft and configured to drive a first functional component, and a second functional portion provided on a lower portion of the crankshaft and configured to drive a second functional component;
• processing the entire crankshaft by a first treatment to at least enhance a corrosion resistance thereof;
• and
• processing at least an entire surface of the coupling portion of the crankshaft by a second treatment to at least enhance a strength thereof;
• wherein
• the first functional portion and the second functional portion are not processed by the second treatment.