Originally Posted by jimmuller

I did notice a derailleur pulley bolt backing itself out once. Whenever I remove a pulley those bolts bother me because they are so small that I could easily strip them with even a small wrench. Of course one pulley rotates in the direction of tightening its axle bolt, and the other in the direction of loosening it. So the key is keeping them lubed and free enough that the bearing exerts little friction on the bolt.

When I'm doing a re-build or repair I often have to leave something loose with the intent to check everything later before a test ride. Most of the time I remember. That's what test rides are for!