Rocker shaft with diamond-like carbon coating

A rocker shaft assembly for a valve train of an internal combustion engine, comprising:

• a rocker shaft including:
• a substantially cylindrical outer circumferential surface;
• and,
• a layer of metal-free amorphous hydrocarbon deposited on the substantially cylindrical outer circumferential surface;
• and, a rocker arm:
• radially disposed about the substantially cylindrical outer circumferential surface;
• in contact with the layer of amorphous hydrocarbon;
• and,
• at least partially rotatable about the rocker shaft.

A method of forming rocker shaft for a valve train of an internal combustion engine, comprising:

• forming a substantially cylindrical outer circumferential surface;
• and,
• depositing a layer of amorphous hydrocarbon on the substantially cylindrical outer circumferential surface, wherein:
• the rocker shaft is arranged to engage a rocker arm such that the rocker arm is at least partially rotatable about the rocker shaft.