The bike I'm doing the conversion on did have a derailer, but the chain tensioner I made was from a different derailer from a different crappy pacific bike. Plus I'm not just using the derailer as the tensioner I took the mount off the old derailer and used it to MAKE a new tensioner. The only reason it dosent fit is cuz the bolt is too big and since it sits in the old derailers spot, it hits the cog.