Crankcase Production (CP) is a company engaged in manufacturing, one of which produces one component of the engine motor unit, namely the crankcase component. In the production process, there are still various indications of waste that cause a decrease in the efficiency and effectiveness of the production process. One of the biggest problems is defects, with a percentage of defects above 5%. Therefore, it is necessary to optimize the process of the crankcase to increase the effectiveness and efficiency of production. This study aims to eliminate waste in the production line of the crankcase by implementing the lean manufacturing concept. The lean manufacturing method used is the Waste Assessment Model (WAM) to distinguish waste in the manufacturing process. The integrated cost value stream introduces cost lines that can help facilitate decision-making. Based on the results of waste identification, the 3 largest wastes were found, namely defects, inventory, and transportation. There are 2 alternative improvements to overcome this waste, namely by changing the jig tool and changing the push-to-pull method. The results show that defect waste decreased to an average of 4.8%, the total value added cost decreased by 1%, total non-value added cost decreased by 55%.