Mike, Tom,


This is exactly what this cut-out is for.

Some engines have a flat in their back-plate, so the uncut piston-skirt will have clearance.


On the rotating crank-web and the rear bearing, such a flat cannot be machined... so the cut-out must be in the piston skirt.


Many engines may have no such 'cut-out' in their original, small displacement version.
But when the manufacturer 'strokes' the engine to offer versions of increased displacement, the piston will have a cut-out at its front; or if there already was one, it will be larger for the stroked version.

This way, the piston can descend further down without hitting anything solid...