Abstract: A side-valve type internal-combustion engine has a cylinder head formed with a recess or recesses each of which forms a combustion chamber with the associated cylinder and which is large enough to permit the alternate flow of suction or exhaust gas between the suction (inlet) or exhaust valve and the cylinder. In plan, the configuration of the recess is generally L-shaped and covers the both valves and part of the cylinder. One leg of the L-shaped recess provides a straight line passage between the suction or inlet valve and the cylinder, while the exhaust valve and the cylinder are connected in series by the one leg of the recess from the cylinder to the suction valve and then by the other leg from the suction valve to the exhaust valve. The height of the recess is reduced in the region directly above the exhaust valve to a level considerably lower than the rest of the recess so that the upper wall surface of the recess is very close to the exhaust valve when it is in its uppermost position.