Item 2 is the chain tensioner - its only job is to take up the slack on the return (non-tension) side of the primary chain drive (the one from the engine to everything else). A sprocket on the tensioner would not change anything. I can't imagine why it would have two sprockets, since there is only one primary chain, unless you twist the link between two sprockets to tension the chain. Sounds like we need to see a picture.
