A ladder frame of an engine is disclosed, in which noise and vibrations are minimized, the installability of the oil filter is improved, and inclusion of air is reduced in the oil flowing from the cylinder head to the oil pan. Inside an elongate rectangular outer block, three partitioning walls are formed equidistantly, so as to form four crank chambers. The crank chambers of the outer block respectively have bottom faces which are not perforated or open but are completely closed. On the side parts of the bottom faces, there are respectively formed oil flow faces which gradually become deeper in the direction of the revolutions of the crankshaft. Among the oil flow faces, those of the first, second and third crank chambers have oil drain holes respectively at their ends. Thus the bottoms of the crank chambers are closed so as to close the space between the cylinder block and the oil pan, resulting in the reduction of the noise and vibrations. |