Free piston engines having a free piston having a first piston diameter in a cylinder with a combustion chamber on a first side of the first piston and a piston rod having a second diameter fastened to a second side of the first piston and extending to a single second piston having a third diameter smaller than the first diameter, but larger that the second diameter, the single second piston extending into a hydraulic cylinder, the second piston having a first hydraulic area defined by the third diameter in a first hydraulic chamber, and a second hydraulic area defined by the area between the third diameter and the second diameter in a second hydraulic chamber, and valving to control the coupling of a high pressure, a low pressure and a reservoir to the first and second hydraulic chambers to control the free piston.