[ChrisH]

There's an even easier way to tesion chain. Take a piece of 1/2" dia delrin rod about 1.5" long or enough longer to bridge whatever gap your chain is runing through. Drill a hole through the center of the rod perpindicular to the axis of the rod about 3/8" from each end. The two holes should be parallel to each other. Slide the rod under the chain but up against some supporting structure until it is just a little too tight. Bolt the rod down. The chain will wear into the rod until it is the right tension. It will then stop wearing into the rod as a sort of equilibrium is reached.

It takes 10 or 15 minutes to fabricate and install.