Cuckoo minute hand stops while time train running

[nan11580]

1-day G M ANGEM countwheel cuckoo. I took apart, cleaned, polished/burnished pivots, oiled. Problem is that the minute hand stops at the 8 with the rest of the time training running … BUT the hand doesn’t stop each revolution. Runs fine for 60 hrs, 48 hrs, etc. then randomly, hand stops at the 8, escape wheel still rotating, time weight dropping.

When I move the stuck hand forward there is a little resistance for a few degrees, then it moves easier. Strike works normally and freely, except paused when minute hand stuck.

What I have done: noted on minute arbor lifting cam where lifting lever tab is when hand stops. Polished/burnished edges of the cam.  Should I grease the cam?  Any suggestions about where to look next? Thanks!

[KeithDoster]

Hi nan11580.  If it were me, I’d try to start eliminating as much as I could. Take the movement apart again (yeah, I know, that kinda stinks) and only run the time train with everything else removed. If it runs for a couple of weeks with no issues, then you can safely assume the problem lies within the strike train or the interaction between the strike and time trains. You’ve already addressed that by checking the edges of the lifting cam, but I assume the problem persisted after you polished it. Should I also assume the minute arbor is absolutely straight? Start there and let us know how it goes.

[nan11580]

Follow up: problem solved, it was  the motion works. Testing in-hand, after several revolutions the idler gear and hour wheel skewed towards each other til they were flat against each other, then friction, and minute hand stops (usually at the 8).  See photo.

What I did:  I replaced the taper pin on the washer of the idler gear. Original taper pin was curved from trying to jam it in the arbor hole.  I replaced with a long flat taper pin, rectangular in cross section. Theory is to apply equal pressure on washer to prevent wobble/skew. After 70 hours testing, the idler gear and hour wheel are maintaining airspace between them.  See two photos showing movement with original curved taper pin and gears jammed.

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