Abstract: Internal combustion engine structure comprising a one-piece cylinder-block and crankcase casting with integral cylinder-head, of light alloy, and incorporating valve guides, induction ports, exhaust ports, spark plug wells, cooling-water chambers open at the upper portion of the casting around the valve seatings and closed by a cover, said cooling-water chambers extending axially around the cylinders and outside the areas corresponding to the induction and exhaust ports and also to the spark-plug wells, said casting further comprising in said areas around said cylinders a wall portion provided with cooling fins, whereby the casting can be obtained directly from a light alloy in a chill-mould, notably according to the known high-pressure casting process.