1966 Bulova 12ECACD (Buren 1321) - seconds hand sweep not fluid

[WhatRainwaterDoes]

I'm servicing a 1966 Bulova Ambassador with rust damage. The watch ran fine prior to service when wound by the microrotor, but the keyless works were rusted out so the watch could not be manually wound or set. I've replaced most of the keyless works (new stem, setting lever and screw, sliding clutch, and first intermediate wheel) and done a service and it now it can be wound and set. It runs great on the timegrapher, +12 s/d, 300 amplitude, 1.1 m/s beat error.

I thought my service was done! When casing the watch, I put the seconds hand on and it does not sweep fluidly around the dial over a minute. In places, it "jumps" like a quartz watch, never stopping, but not moving at a consistent rate. What I've tried/noticed:

• The issue is only with the seconds hand installed. Under a microscope, the pinion rotates freely and normally when the hand is not in place
• The issue is the same with the dial, hour and minute hands, hour wheel and cannon pinion all removed, so it can't be friction against those parts
• I recleaned and relubricated the seconds pinion and bridge and it didn't help. The pinion pivot appears to be intact and set within the jewel properly, with a normal amount of end shake
• The hand moved freely prior to my service as far as I remember, or at least I didn't notice any issues

Given all the above, the only thing I can think of is that the extra weight of carrying the seconds hand is causing an issue with the setting inside the mainplate, but I'd have no idea how to "peg out" the long tube, and I'm really reluctant to strip the entire 30 jewel movement down again to reclean the mainplate unless I have no other choice. Any suggestions?

[WhatRainwaterDoes]

I think I've got a diagnosis. The end shake is too much and the seconds sweep seems to be fluid while movement up, which probably means I've got a worn seconds pivot. I'll see about replacing it.

[JohnR725]

We really need a picture of your watch to see how the secondhand is being driven otherwise we get to guess

8 hours ago, WhatRainwaterDoes said:

seconds pinion

.Usually with separate pinions There can be a spring that pushes against it to hold it in place. Otherwise I have a habit of flopping around which is exactly what you're seeing.

[Neverenoughwatches]

8 hours ago, WhatRainwaterDoes said:

I'm servicing a 1966 Bulova Ambassador with rust damage. The watch ran fine prior to service when wound by the microrotor, but the keyless works were rusted out so the watch could not be manually wound or set. I've replaced most of the keyless works (new stem, setting lever and screw, sliding clutch, and first intermediate wheel) and done a service and it now it can be wound and set. It runs great on the timegrapher, +12 s/d, 300 amplitude, 1.1 m/s beat error.

I thought my service was done! When casing the watch, I put the seconds hand on and it does not sweep fluidly around the dial over a minute. In places, it "jumps" like a quartz watch, never stopping, but not moving at a consistent rate. What I've tried/noticed:

• The issue is only with the seconds hand installed. Under a microscope, the pinion rotates freely and normally when the hand is not in place
• The issue is the same with the dial, hour and minute hands, hour wheel and cannon pinion all removed, so it can't be friction against those parts
• I recleaned and relubricated the seconds pinion and bridge and it didn't help. The pinion pivot appears to be intact and set within the jewel properly, with a normal amount of end shake
• The hand moved freely prior to my service as far as I remember, or at least I didn't notice any issues

Given all the above, the only thing I can think of is that the extra weight of carrying the seconds hand is causing an issue with the setting inside the mainplate, but I'd have no idea how to "peg out" the long tube, and I'm really reluctant to strip the entire 30 jewel movement down again to reclean the mainplate unless I have no other choice. Any suggestions?

Does the same thing happen through all dial positions? 

[WhatRainwaterDoes]

Photo enclosed. There is no spring to hold the pinion down but there is a washer underneath between the pinion and mainplate. The condition is worse dial up than dial down. 

[JohnR725]

13 hours ago, WhatRainwaterDoes said:

There is no spring to hold the pinion down but there is a washer underneath between the pinion and mainplate. The condition is worse dial up than dial down. 

It's explained in the service manual that the washer has a purpose it just doesn't go into great detail as to whether the Washer is flat or curved or exactly how it works. But it is very important if you want your Sweep to work correctly

Bulova 12 EBA Series.pdf

[WhatRainwaterDoes]

19 hours ago, JohnR725 said:

Usually with separate pinions There can be a spring that pushes against it to hold it in place. Otherwise I have a habit of flopping around which is exactly what you're seeing.

I solved the problem on my own while waiting for my follow up posts to clear moderation, but it was this that gave me the clue. The washer is curved and I had it upside down. I'd never seen a washer on a watch before except between the hour wheel and the dial, and I was used to orienting them "bowl-shaped", but it never occurred to me that the tension needs to push on the moving part. In this case, the washer needs to be oriented "dome-shaped" to put tension on the seconds pinion. Thanks for indirectly giving me the key!