The tensioner includes a cylinder inside a large capacity reservoir tank without interference with other components. The tensioner maintains oil inside the cylinder at all times, thereby improving the response of the tensioner when the engine is re-started after a long periods of inactivity. This prevents any fluctuation and wear and tear of a timing chain during engine re-start. Furthermore, the reservoir tank is integrally cast with the cylinder block to reduce manufacturing costs and increasing space-utilization of the engine.