if a rope was run through the rear wheel and the bike suspended in a such a way to apply tention to the lower chain run as it was hanging nose end down from the ceiling,then connect the chain on the upper run as snug as possible by hand,at this time you will only be livting a 12 inch or so piece of chain to make the connection and all excess play suould be held tight with the rope and motor compression,that is as tight as is expected and the idler and spring idler may or may not be needed it is mainly to clear the chain stay on narrow problems,,, ,and to avoid chain wipping ,the teeth on the sprockets need to be beveled correctly and sprokets aligned properly to eliminate chain occilation which acts like a bearing slide hammer on the little components
the motor needs to be mounted in a way that there is positive ,absoluty no play,frame contact not dependent on the little bolts to do more than look nice holding parts in place, not act as 5/16-3/8 ths muffler clamps forcing things to bend into place to hold