I had the same problem...could not move the sprocket or motor. I wanted to use 26X2.25 balloon tires. What I had to do is go to 26X2.00 tires. It still rubs a little...but after 5 years and 4,000 miles the tire is still holding strong.
For the tensioner, some use a sheet metal screw or bolt or both to keep the tensioner from getting into the wheel...
chain tensioner modification