Ever since my very first days of watchmaking school I have given the gear train a good spin during assembly before installing the escapement. This is an opportunity to check and see that all the wheels turn true and free. It is extremely rare that I encounter a problem at this phase, since I diagnosed problems and replaced parts during disassembly.
It may seem like this exercise is futile given that I discover a problem maybe once a year this way. Today was one of those days however. The gear train was noisy and didn’t turn freely, in fact it would hardly turn at all in one direction. After considerable investigation I determined that the newly installed fourth wheel (received from the factory) was incorrect for this model. It fits well in the watch, it has the same length shaft, even the endshake was correct. Unfortunately this one has one fewer spoke, and I can only conclude that it belongs in a different watch. I did not take the time to count teeth or pinion leaves, because I will just replace it with the correct part.
Conclusion: I’ll just keep spinning my wheels as a watchmaker 🙂