Engine balance shafts supporting structure

A casing accommodating therein a pair of balance shafts (8,9) below the cylinder block (3) comprises an upper casing (10a) and a lower casing (10b) that can vertically be split, and an oil pump body (7a) is molded integrally with one of the upper and lower casings. In addition, one end of each of the two casings is inserted into the oil pump body for support therein, and the two balance shafts are each supported on a bearing provided between the two casings in such a manner as to be split into two halves at an intermediate portion or the other end thereof. With this construction, the oil pump body can be molded together with the casing, thereby making it possible to reduce the number of components used and man hours for assembling. In addition, since the bearings can be split into two halves, when compared with other portions of the balance shafts, the journal portion can be thinned, thereby making it possible not only to reduce the sliding friction but also to make the casing smaller in size and lighter in weight. More over, the degree of freedom of designing balance shafts can also be improved. With the balance shaft supporting structure for an engine the durability of a balancer, as well as the degree of freedom of designing the same are improvided without making the engine larger in size and increasing the number of components used.