In the shop floor, cracking issue was noticed during assembly of valve seat and valve guide in the engine cylinder head, especially near the valve seating area. This paper reveals a non- linear finite element methodology to verify the structural integrity of a cylinder head during valve seat and valve guide assembly press-in operation under the maximum material condition, i.e., smallest hole size on cylinder head for valve seat and guide and largest diameter of valve seat and guide. Material and geometrical nonlinearities, and contact are included in this method to replicate the actual seat and guide press-in operation which is being carried out in shop floor. The press-in force required for each valve seat and valve guide assembly is extracted from simulation results to find out the tonnage capacity of pressing machine for cylinder head assembly line. Stress and plastic deformation due to assembly load are the criteria checked against the respective material yield. Further the tolerance such as roundness and centre point shift are evaluated for valve seats and valve guides and verified with design specification of the cylinder head assembly. This method is also used to evaluate the different assembly pressing process and optimize the pressing sequence for valve seats and valve guides assembly. This method allows design engineers to identify structural weakness at the early stage or to find the root cause of engine cylinder head failures. As a result, the failure rate of valve seat and valve guide assembly would be minimized through the analysis and consequently reduce the cost of physical trials in the shop floor.