to simplify the connection of a cylinder barrel and a cylinder head to , a crankcase and to reduce the weight of an engine . a liquid - cooled engine is provided with the crankcase wherein a cylinder barrel having a water jacket on the cylinder side for cooling is connected to the crankcase . a cylinder head is connected to the cylinder barrel . a plurality of mounting bosses extend from fitting planes to a crankcase of the cylinder barrels and to cylinder heads that are integrated with cylinder blocks . the cylinder barrels and the cylinder heads are integrated in a state in which the mounting bosses encircle the cylinder bores and the cylinder blocks are fastened to the crankcase by bolts inserted into each mounting boss .