The mobility method of dynamically loaded journal bearings was applied to optimize the lubrication of the main journal bearing of the crank press. The effects of oil viscosity, temperature bearing clearance, length, the existence of the circumferential groove, peak press force, and crank rpm were examined. From the results of the minimum film thickness and the maximum film pressure, some of the factors could be optimized, and the degrees of the beneficial and detrimental effects of the others could be estimated.