A single-shaft dual expansion internal combustion engine includes first and second power cylinders and an expander cylinder. The cylinder head fluidly couples the first and second power cylinders and the expander cylinder. First and second power pistons reciprocate in the first and second power cylinders and connect to a first crankpin of the crankshaft. A multi-link connecting rod assembly includes a rigid main arm supporting a first pivot pin, a second pivot pin and a third pivot pin. The first pivot pin connects to an expander piston reciprocating in the third cylinder. The third pivot pin couples to a first end of a swing arm, and a second end of the swing arm rotatably couples to a fourth pivot pin that couples to a distal end of a rotating arm that attaches to a rotating shaft coupled to rotation of the crankshaft.