and so the diameter of the second section 23 of the cylinder equals to the outer diameter of the sleeve piston 40 the intake way 11 and the exhaust way 12 are located at the highest place within the second section 23 the bottom of the cylinder 10 provides a retaining ring 24 employed for holding the compression spring 25 which touches the bottom of the sleeve piston 40 and also offers a uprising force to the sleeve piston 40 as shown in fig4 the piston 30 is placed in the first section 23 of the cylinder 10 and the compressed gasoline is sealed by the piston ring 31 the sleeve piston 40 is located at the upper dead point of the second section 23 of the cylinder 10 the sealing rings 43 44 are located below the intake way 11 and exhaust way 12 to stop the engine oil 19 leaking out of the crank case 16 and entering the intake way 11 and exhaust way 12 as shown in fig5 immediately after the spark plug 18 ignites an explosion of the compressed mixture of gasoline and air the main piston 30 begins to move downward and move into the chamber 41 of the sleeve piston 40 and touches the groove race 42 so as to bring down the sleeve piston 40 together the intake way 11 and the exhaust way are respectively opened similar to the prior art of the tow stroke engine and the spring 25 is compressed when the main piston 30 arrives at the position as shown in fig6 the rotary force from the crankshaft 17 turns the main.