A control system for an adjustment device for a variable compression ratio engine comprising: a jack head, a jack piston, a sprocket wheel, a movable transmission member, and a control valve. The jack piston is received within a chamber of the jack head defining first and second fluid chambers. The control valve controls the flow of fluid between the first and second fluid chambers. Based on the position of the control valve, fluid flows from the first fluid chamber to the second fluid chamber or vice versa, moving the control rack connecting the jack piston to the sprocket wheel. Reciprocating motion of the sprocket wheel adjusts the position of the cylinder of the engine.