Audels Engineers and Mechanics Guide 4 is part of Frank D. Graham’s eight-volume series covering modern engineering practice. First published in 1921, the collection served as a practical course of study and reference for engineers, mechanics, electricians, and industrial workers.

Volume 4 focuses on diesel, gasoline, and oil engines, along with producer-gas systems. Its question-and-answer lessons explain internal-combustion principles, ignition, fuel delivery, engine timing, lubrication, cooling, performance, and maintenance.

The volume uses diagrams and calculations to help readers understand how engine adjustments affect power and efficiency. The illustration beside the title page includes examples of ignition timing and other engineering principles used to evaluate mechanical performance.

This book documents the period when internal-combustion engines became increasingly important alongside steam power. Its inclusion in the collection helps show how engineers adapted as industrial power technology continued to evolve.