This book will discuss the Otto-cycle internal combustion engine, and its mobile and fixed components with a focus on maintenance. The objective will be to disseminate knowledge regarding the technical procedures performed in engine repair, using a didactic approach that is easy to understand. The operation and work cycle of the engine will be the first chapter, dealing with the theoretical cycle of the alcohol and gasoline engine. The second chapter will deal with the main parts of the engine, defined as fixed and moving parts. Chapter three will deal with the lubrication and cooling systems and some aspects of preventive maintenance. The fourth chapter will address the measuring instruments applied to engines in repair, an important topic to clarify the importance of metrology. The last chapter of this work develops metrology in engine repair and in its fixed and mobile components.