Oil pan structure for an engine

In an example, an oil pan 8 comprises a bottom plate 26, a vertical wall 27 integrally protruded upwardly from outer edges of the bottom plate 26, an outwardly extending flange 28 formed integral with the vertical wall 27 at the protruded end and fixed to the lower end of a crankcase 2, a pair of bosses 21, 21 located below the outwardly extending flange 28 and integrally projecting laterally outwardly from the outside surface of the vertical wall 27 for supporting a component 14 of an engine 1, and a connecting piece 29 disposed between these two bosses 21, 21 for connecting the two bosses 21, 21 integrally. The bottom plate 26, vertical wall 27, outwardly extending flange 28, bosses 21, 21 and connecting piece 29 are formed by casting. The inner edge 29a of the connecting piece 29 on the side of the vertical wall 27 is formed integral with the outwardly extending flange 28. Such an arrangement can prevent shrinkage cavities from being produced when a pair of bosses are provided on the outside surface of a vertical wall of an oil pan made by casting and these bosses are reinforced.