A few months ago I had a unit with a hour wheel that just spun freely. The little itty bitty toothed gear under the wheel had come loose. I dug through my parts bins and found one, installed it and all was OK. Yesterday I ran into another one with the same problem. Wondering which end of the little gear went against the bottom on the wheel I used a 10x loupe to inspect it and discovered that it was threaded and so was the bottom of the larger wheel. I thought it was a press fit. Using a nylon jawed plier I tightened it up and it is also working good today. I am a relative newbie and always will be a newbie, but for those of you that have not yet discovered this, I thought I would post a little note on the subject.

That gear that unscrews is called the safety pinon. It unscrews when the mainspring breaks or the click is unhooked from the ratchet wheel.
I ran into that problem myself when learning. One lesson I also learned is never use a pair of pliers to tighten that gear. Some of the gears are brittle and a tooth will break off with to much torque. I now use a pair of tweezers with teeth to hold the gear and then tighten it slightly with my fingers.

Jim, So it is possible that I caused the gear to spin loose while letting down the MS by sticking a pin in the ratchet release hole. Neither units had a broken MS. The nylon tip pliers I mentioned have a very soft grip, kinda like a pair of battery tweezers and are parallel closing.

Yes its possible thats what happened. If you have bench winders to wind movements that are out of the case make sure one is in the movement so that when you stick the pin in you can slowly let the tension off the spring by slowing the winders spin. If you dont have them make one with an stem and a crown and do the same thing.

I like that idea. I have been putting pressure on the hour wheel to keep it from spinning to fast or the ratchet wheel.

Patrick,
I'm far from an expert, but what I do is put a stem into a pin vise and hold the pin vise to allow it to unwind slowly. I picked up a large quantity of stems here and there, usually have the right one when needed.
Bill

A bench winder is one tool I feel is essential. This is especially true with 18s watches where the mainspring release can only be accessed with the movement out of the case. The home made one with the stem and pin vice sounds good but they are available from time to time and worth the investment.

Thanks all for your replies. I found a way to do it with a leather washer by retarding the speed of the wheel as it unwinds.