- To reduce size of the engine.
- To reduce crankpin dia.
- If not oblique cut not able to lift same from top with piston.
- If not oblique cut have palm bolts ,increase in production cost.
- Apart from this , as engines are becoming more efficient the liner bore dia is not increasing but as the power output is increasing the bottom end bearing size is increasing , because it has to transmit so much of the peak pressure (downward thrust) .Because the thrust is increasing the bottom end bearing size has to increase , liner dia and bore remains almost same.
Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole. More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out. To compensate for the loss of material in the shell due to opening, a doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the dirrection in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as the stress in this direction is maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating Circumferential stress: Pd/4t More over a considerable material and weight saving is achieved as minor is along the direction of maximum stress.