The correct selection of rough datum and the reasonable design of initial positioning fixture are crucial issues in the processing process.

When positioning the side of the connecting rod, the rough datum positioning method of the connecting rod datum end face and the outer circle of the small head blank at three points and the outer circle of the large head blank at two points is adopted.

This can ensure that the machining allowance of the large and small head holes and the covered machining surface is uniform, the weighing of the MG Roewe Maxus Engine is uniform, and the shape and position of the part assembly are guaranteed.

In the processing of Bare Engine, the processing positioning method of the rod end face, the top face of the small head, the side face and the side face of the large head is adopted.

In the processing of Bare Engine from the oblique joint surface of the bolt hole to the stop, the processing positioning method of its end face, the two seat faces of the bolt and one bolt seat face is adopted.

This positioning and clamping method with high repetitive positioning accuracy, stable and reliable can make the parts less deformed and easy to operate, and can be used in various processes from rough processing to fine processing.

Due to the uniform positioning datum, the size and position of the positioning points in each process are the same. These provide good conditions for stabilizing the process and ensuring processing accuracy.