An engine and a motor are actually two different things and should not be confused in your writing.
AP Style states that an engine develops its own power, usually through internal combustion or the pressure of air, steam, or water passing over vanes attached to a wheel. Some examples of engines would be automobile engines, airplane engines, tractor engines, missile engines, turbine engines, etc.
A motor receives its power from an outside source. Some examples of motors are electric and hydraulic motors.