Machining defects for the valves used in engines have also recorded high rejection level in Dent & Damages and Stem Roughness hence the quality of valves produced is compromised and the cost of producing them highly charged. These questions form the focal research concerns of this work; which utilize the Six Sigma DMAIC (Define, Measure, Analyze, Improve, and Control) rigorous frameworks. For Dent & Damages, the possible cause was found to be the metal to metal contact when unloading, which has therefore been resolved by placing polypropylene (PP) layer onto the output chute. In the case of Stem Roughness, the frequencies of replacing the grinding dresser were too spaced out, a situation that stemmed from the lack of an efficient method of tracking the dresser’s state and expiry time. A solution was developed where changing of the dresser was synchronized with an automatic alarm, such that the machine was switched off after an expiry of the set limit of dresser usage. These interventions helped to reduce the defects significantly and proved that using DMAIC methodology in industry can help to enhance both the product quality and the production processes. Defects in engine valve manufacturing were reduced significantly by addressing root causes: metal-tometal contact was mitigated using a polypropylene (PP) layer, and irregular grinding dresser changes were resolved with automated alerts. Rejection rates decreased from 2.86% (Sigma Level 3.5) to 0.27% (Sigma Level 4.3), improving quality and operational efficiency. The Six Sigma DMAIC methodology proved broadly applicable for process optimization in manufacturing.