Having a hard time envisioning this: what actually keeps the stem from pulling all the way out? Is it just the tip of a little screw?

 

I'm not sure learning new stuff is allowed on a holiday, but I had no clue either. I still don't know what's going on inside, but this was interesting nonetheless.

 

The stem is held in place with the set lever, which has a small pin on it that mates with a grove in the stem.

The set lever can either be secured by a spring, where there isn't a screw head only a push piece to release it, or a screw, where you loosen the screw until the set lever pin is clear of the stem grove and able to be removed.

Rob

 

Only photo I could find on short notice...here you see a setting lever and setting lever screw from an Omega Cal. 285...



They were both replaced due to condition, but the red arrow shows the small pin that catches in the groove on the stem. The internal portion of the tube that you see is threaded, so this part is flipped over and pushed into a hole on the dial side, then the screw is threaded in from the wheel train side.

Cheers, Al

 

Thanks Rob and Al. A quick search for setting lever and stem surfaced diagrams to help, um, put all the parts in place.



http://collectorebooks.com/watch2/watch01.htm

 

Thank you, gents. A picture is starting to form...

So, I don't know if the little diagram below is representative of the average stem. Would the red arrow tip intersect with the area on the stem between "C" and "B"?

 

Yes.

 

In thinking through how the stem and sliding pinion function, it occurred to me that on a non-hacking movement, the pulled out stem would be turning along with the hands. Pretty obvious I suppose, but I had never thought about it.

I dug out my Gyromatic with a signed crown and sho'nuff, it's turning.

 

Thanks. It looks like the post on the set lever has a slight concavity - is that how they come, to mate better with the convexity of the stem; or does it "wear" into that shape over time? Further, do set levers need to be replaced typically, or only occasionally over many years of wearing?

 

The concavity is a result of wear, not a typical feature. On a properly fitted set lever the post should not bottom out on the stem grove, it should clear the bottom of the grove only slightly when fully seated.

Not often that the set lever itself wears out, mostly on a threaded one the threads get damaged over time from mulitple uses, and the other common wear issue is the hole for the stem in the mainplate, that enlarges over many years and results in the stem not being held in place, the fix is to custom make a stem that fits snug in the enlarged hole.

Rob