Going to work yesterday I thought that my pedal drive felt just a bit strange.
So I came out during the day to adjust my rear wheel. I found that the chain tensioner roller was completely missing. No sign of it. After thinking about it for a bit, I came up with a decent substitute.
emergency chain tensioner 01.jpg
It's a machine screw. I didn't even bother to check size or length. I suppose it was an inch and a half or so. Double-nutted to the chain tensioner bracket.
Then on the chain side I filled the shaft of the screw with washers that fit loosely on the screw. They'd do the same thing as a roller would. Double-nutted the end to hold them on.
emergency chain tensioner 02.jpg
I only had to go about 12 miles before I could get my spare roller on there. But it worked so well that I think I could have ridden indefinitely.