A reinforcing insert for an engine block (10) formed of an engine block material is provided which is positioned in the bearing saddle area of the block for increasing the strength and stiffness of the bearing saddle area to ensure a secure connection of the main bearing cap throughout engine operation thereby ensuring proper crankshaft support and operation. The reinforcing insert (12) is formed of a material having a higher modulus of elasticity than a modulus of elasticity of the engine block material. The insert includes a lower transverse surface for positioning at a lowermost position in the engine block, an upper surface (36) positioned farthest from the crankshaft, a first and second linear side surfaces (18a,18b) for positioning on opposite sides of the crankshaft. The linear sides extend from the lower surface (22) along respective planes in nonparallel relation to each other. The linear sides may extend either in a converging or a diverging manner from the lower surface. Alternatively, the insert may include two cylindrical inserts positioned in bores formed in the block on opposite sides of the crankshaft. These insert designs provide strengthening and stiffening of the block over an optimum area while permitting secure attachment of a main bearing cap to the block.