During cylinder block and cylinder head assembly, the traditional cup-plug pressing operation is based on process and equipment that are dedicated to a single assembly line. This approach no longer matches the demand for a quick change of assembly line setup to satisfy customers’ responses in the automobile industry. Furthermore, the pressing operation is performed in multiple separate operations across the assembly line. As a result, it is difficult to control the cost and quality of the pressing process. To address this issue, a flexible cup-plug pressing operation was introduced in the engine assembly line. The quality of a flexible pressing operation is determined by the component design, fixture design, support pad mounting location, pressing parameters, and assembly load. It would be extremely time-consuming to evaluate all these factors either empirically or through physical trials. In this paper, a finite element (FE) method was developed to evaluate the quality of flexible pressing process to ensure the first-time-right implementation in cylinder block and head assembly lines and thereby reduce scrap rates and machine downtime. This method optimizes the size and location of pads by evaluating their contribution in taking up the assembly load. A good correlation was observed between predicted and measured press-in force and support pad contribution.