Hi.

I've been having a problem with setting the time of my Benrus BB4 movement (ETA 900) after the stem popped out and I put it back in place.

the stem works fine for winding and when not pulled out turns easily in either direction, though I intend to replace it due to obvious wear. I ordered a three pack of NOS stems.

The problem is that after restoring the stem , first cleaning it of some old grease and wiping with a cloth lightly moistened with oil, it has become increasingly hard to turn the stem to set the time forwards. Near impossible now. since the watch gains a few seconds per day I have found that a tiny bit of back pressure on the stem will momentarily stall the movement so it gets back in line. I certainly don't wish to do this much at all.

I'm thinking that whatever mechanism that disengages the hands from the movement to allow free motion in setting when the stem is pulled out isn't working, probably jammed with debris of some sort.
I suppose the narrow probe at the end of the stem controls this.

I've never seen anything on how this mechanism works or is constructed.
The winding bridge looks to be separate from the rest of the mechanism. In looking at parts movements I saw one with that bridge removed.
I don't want to attempt a cleaning or repair of this till I know exactly what to expect to find.

Any information , directions to a resource or advice is appreciated.

PS
I did find this short video.

 

That's the cannon pinion. It doesn't actually "disengage" the hands, just allows then to turn when the friction of the cannon pinion is overcome by the torque you are applying with the crown via the setting mechanism. The pilot diameter on the stem is not involved in this process.

This is a very basic movement with a very common setting mechanism and cannon pinion, and likely it just needs a service.

Although I can't find a tech guide for this specific movement, if you look for one for an ETA 6497 it will give you the information you need.

Cheers, Al