I spend a lot of time examining parts looking for defects. In order to be a really efficient watchmaker you have to be able to see the defects and correct them during the disassembly of the watch. If you don’t find them until you have reassembled the watch you end up having to partially (or fully) disassemble the watch and re-clean components in order to correct the problem or replace the part.
Sometimes, however the defects are invisible (or imperceivable). This happened to me recently. I received a dive watch with a bezel that would not rotate. Usually this is because there is so much junk under the bezel that it is stuck in its current position. As usual, I removed the bezel and spring and thoroughly cleaned everything. It all appeared to be in good condition so I lubricated the parts and reassembled the watch. The bezel still wouldn’t turn! I repeated this several times (like banging your head against the wall) and got the same results.
Since the bezel is a simple apparatus I assembled it without the spring and found that it turned free and smoothly so I pulled a new spring out of the drawer and replaced what appeared to be a perfectly good spring with a new one. This cured the problem. On further examination I still could not see the defect in the old spring – but there was something definitely wrong with it, I just don’t know what.
What is the lesson here? Watches are simple machines and sometimes there is only 1 or 2 things that can possibly cause the problems you are seeing. When you can’t “see” the problem, a little trial and error can produce the results you need.