Needed a chain tensioner because that modified hub isn't perfect and the way in which I mounted the swing arm and fabricated the JS plates just made the chain routing too close to the swing arm. I didn't like any of the commercial mini bike offerings, with a silly little spring and a skate board wheel. It might be fine for some applications, but not mine with this much weight, and a tire shredding four horsepower Tecumseh with a cam and a carb and a high rise intake manifold and headers.
So knowing this is not brain surgery, or curing cancer, I spent about two weeks thinking about it and writing stuff down, and looking at motorcycle tensioners out there for $100 and made this thing. If you want to know more about it, or lessons learned or parts used, PM me, although (see brain surgery comment) I will have forgotten already.
Parts I made and used. Torsion spring is 19 LBS.
Assembled. Can you find the Tecumseh alignment dowel?
Upside Down. Honda XR Brake Anchor Arm shown.
Shitty Welds, but they hold.
Right Side Up
From the Side