If the nut was too far on the threads then the washer wasn't thick enough. I went through this in 1996 with a '67 Barracuda that I bought. The car was overall in decent condition, but had a sloppy idler. There are no washer. Put a thick washer on and had no more problems with a sloppy idler. I only kept that in a few years. The next time the car went together was with a home built DC k-member and a 383...