It would take a book with many pages to answer the questions ask in there entirety. Coupling two or more engines challenges the builder to cope with
mechanical physics that don't want to cooperate. I can think of a few, possible on the VOC web that are our brothers that have took on the challenge.
Neil Diggens Dad coupled two Triumph's together using the crank coupling gears from an Arial Square Four. Dan Smith coupled two Harley's. Dave Matson
has coupled two Vincent's, while in the service he coupled THREE Vincent's. Many attempt's have been made, the failures in the endeavor far out number the successes . Having been told this by those that have tried, spending a couple of decades watching doubles at the drags spit there coupling chains with regularity, I decided to build a test bead to find out what physics were involved in the coupling of two engines . On my son' s video that he made for a birthday present, you will see a double engine Mustang motor/scooter, the white bike. That is the quickie I glued together for the test bead. After an extensive test project for real life going on's , I came to the conclusion to make happy the coupling chain , it was paramount to have the front engine lead the rear engine in its ignition firing by 10 degrees. All other attempts like firing the engines 180 degrees apart proved unworkable, shedding the chain in short time . All other combinations had the same results. ( more later)
Max
excuse the sp