Patent ID: 7086356

Claim:
An engine cooling structure in which cylinder barrels having cylinder bores and cooling cylinder water jackets are coupled to a crankcase with a crankshaft rotatably supported therein, cylinder heads having head water jackets communicating with the cylinder water jackets are coupled to the cylinder barrels with combustion chambers defined between the cylinder heads and the cylinder barrels, pistons slidably fitted in the cylinder bores have top ends facing the combustion chambers, and a water pump for circulating a coolant between the cylinder and head water jackets is mounted on the crankcase on one end thereof along the axis of the crankshaft comprising: coolant supply passages formed in said crankcase for guiding the coolant from said water pump; coolant return passages formed in said crankcase for guiding the coolant led from the cylinder water jackets; said coolant supply passages and the coolant return passages extending substantially parallel to the axis of said crankshaft with the axes of said cylinder bores being disposed therebetween and said cylinder water jackets and said head water jackets are formed such that the coolant supplied from said coolant supply passages returns from said cylinder water jackets through said head water jackets to said cylinder water jackets, wherein said cylinder water jackets are formed in said cylinder barrels for being divided into a supply jacket portion communicating with said coolant supply passages and communicating with said head water jackets and a return jacket portion communicating with said coolant return passages and communicating with said head water jackets at a position spaced from said supply jacket portion, and wherein said supply jacket portion and said return jacket portion, with superposed portions surrounding substantial halves of the cylinder bores, are formed in the cylinder barrels having the cylinder bores arrayed in the axial direction of the crankshaft and a plurality of supply and return branch passages, which connect the regions of said supply jacket portion and said return jacket portion that correspond to the cylinder bores to said coolant supply passages and said coolant return passages are disposed in the crankcase and the cylinder barrels at each cylinder bore.