Six Sigma is one of the popular methodologies used by the companies to improve the quality and productivity. It uses a detailed analysis of the process to determine the causes of the problem and proposes a successful improvement. Various approaches are adopted while following Six Sigma methodologies and one of them is DMAIC. The successful implementation of DMAIC and FTA is discussed in this paper. In this study, the major problem was of continuous rework up to 16%, which was leading to wastage of man hours and labor cost. Initially, fault tree analysis (FTA) was used to detect the key process input variables (KPIVs) affecting the output. Multivariable regression analysis was performed to know the possible relationship between the KPIVs and the output. The DMAIC methodology was successfully implemented to reduce the rework from 16% bores per month to 2.20% bores per month. The other problem of nonuniform step bores was also reduced significantly. 1. Introduction Diesel engines have very wide applications in this modern technological era. They are designed to cater for the need of construction, mining, power generation, locomotives, marine transport, compressors, and so forth market segments. These are heavy power requirement applications. For such applications, the output requirement may vary from 10 horsepower to 3500 horsepower. The engine with this huge power output is also huge. The firm in which this study was conducted was involved in manufacturing 1？V- and 16？V-cylinder diesel engines. The sand casted engine block went through various operations and then was assembled. Operations like undercutting, water clearance chamfer, boring, step-boring, and so forth were performed on each cylinder. The step-boring operation was the most difficult operation. It needs special attention as the liner is resting in it. A cylinder liner is pressed into an engine block and houses the piston. The cylinder liner is much harder than the engine block and prevents the piston from wearing out through the cylinder bore. Typically used in aluminium engine blocks and diesel engines, the cylinder liner is either pressed into position or held in place by the cylinder head. In large engines such as the engines found in diesel locomotives, the cylinder liner is part of an assembly containing a new piston, piston rings, and a connecting rod. During scheduled maintenance or repair, the liner is changed as a complete unit. In aluminium engine blocks, the block material is too soft to house a piston. The friction of a piston moving up and down inside the alloy block would make
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