Abstract: A piston assembly includes a piston having a crown with an upper combustion surface with a cylindrical outer surface extending downwardly from the upper combustion surface. A pair of pin bosses depends from the crown to a pair of pin bores having generally cylindrical bearing surfaces aligned along a pin bore axis with a top wall portion extending between the pin bosses. The top wall portion has a concave bearing surface forming a continuous concave bearing surface with the pin bores. A separate skirt is fixed to the piston against relative movement. At least one rib extends upwardly from the top wall portion of the piston on opposite sides of the pin bore axis to a lower wall surface of the crown. The at least one rib joins the crown to the top wall portion to provide structural support to the top wall portion against unwanted deflection.