The disclosure provides engines or pumps that includes a rotatable shaft defining a central axis A, the shaft having a first end and a second end. The shaft can have an elongate first island disposed thereon. The first island can have a body with a volume generally defined between front and rear surfaces that are spaced apart. The front and rear surfaces can lie in a plane parallel to a radial axis R. The perimeters of the front and rear surfaces can define a curved perimeter surface therebetween. The engine or pump can further include a front side plate disposed adjacent to the front surface of the first island, and a rear side plate disposed adjacent to the rear surface of the first island. The engine or pump also includes a first contour assembly disposed between the front side plate and the rear side plate.