Hello Machies, Thanks for being here for my question. Without wasting time let me take you to my question. As you all know that in 2 stroke engine there are two strokes. First one is for expansion (exhaust) and the second one is for compression (ignition). It's self explanatory that why piston goes downwards in expansion stroke.. But immediately after the 1st stroke why automatically piston goes upwards? Is there any force that makes piston to move upwards? Your answers are greatly appreciated.