This book presents each of the distinct engine epochs chronologically in its own chapter, including profiles of archetypal motorcycle models best associated with each engine. Images of a select variant most representative of each engine era illustrate the introduction of each chapter. Further details on these highlighted engines are given in the pages for the specific model from which each was taken. More than 40 classic Harleys are portrayed in detail, from the first "Model Number 1" F-head single of 1903 to the Pan America adventure tourer of 2021, powered by Harley's state-of-the-art liquid-cooled Revolution Max engine. In between, the development of the Harley-Davidson engines is traced as a gradual evolutionary process, reflecting how the brand's unique classic V-Twin characteristics--hearkening all the way back to the F-head 45-degree layout--came to define an attitude, emotion, and lifestyle, fostering a company maxim: "If it ain't broke, don't fix it."