As you may have noticed from the pictures in the last post, the bottom bracket, cranks, and chain ring are all installed. To convert a double chain ring to a single you'll either need to buy shorter sleeve nuts or be cheap like me, file them down one by one. Two pieces of advise for doing this: firstly, flip the nut over and thread the bolt through the crank to hold them in place while you file. Secondly, use a bigger file than I did. I must have looked like primitive man trying to start a fire as I was squatting on the floor filing away in the middle of the night.