[rotorwrench]

The direction of rotation sets the thrust side. When a connecting rod is going down on the power stroke in a clockwise rotating engine (as viewed from the front), the piston thrusts the opposite direction. In the case of the model A, the thrust side is toward the valve chamber. Split skirts are for piston expansion as they heat up but that spit is a weak point on the skirt so you don't want the split on the thrust side.