Motorcycle Modification is an important part of the total experience for many motorcyclists either in the search for individuality, to make improvements or to make the machine more suitable for their use.  It also supports a whole industry of parts suppliers, modifiers and manufacturers as well as providing the opportunity for all types of individual effort. All types of modification have one thing in common, the overriding need to see that the change does not make the machine less safe to ride than the original. This book proposes a simple method, based on long established aircraft and aero engine practices, of reviewing any intended modification at an early stage so that any potential safety problems can be avoided. The book is more than just a basic manual and incorporates many memories from a long career, various related and unrelated thoughts and a few original and possibly controversial suggestions which occurred to the author at the time of writing. It invites the readers to either agree or disagree with any or all of these deviations from the basic method. The book avoids much engineering theory to ensure that it is readily understandable to those motorcyclists who do not claim to be professional engineers but are contemplating modifying their machines or are just interested in all thing mechanical. Originally published in 2020, the opportunity to produce a 2nd Edition has allowed it to be updated to 2024.  During that time I have concentrated on conversion of two wheeled machines into three wheelers and have learned a lot about the practical problems of this type of modification. The 2nd edition has provided the opportunity to add a new section in the hope of helping anyone thinking of doing this type of modification to avoid many of the problems with this type of change. Forward into the future but not forgetting lessons learned from the past. What-ever projects come along, the principles of failure analysis which are the basis of this book will remain the best way to ensure safety.