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Bulova 6CF Movement

Folkvisor

By Folkvisor
in Watch Repairs Help & Advice

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Folkvisor Super WRT Addict

Folkvisor

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The 6CF I have will work as long as pressure is applied to the stem, as in winding pressure - it need not actually be turned.

The pallet fork moves fine and the balance wheel is fine when it is replaced without the pallet fork being in place.

The watch wants to work. I just don't know where the problem lies but there is some friction somewhere.

Maybe the mainspring is shot.

 

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Folkvisor Super WRT Addict

Folkvisor

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The watch has been cleaned, lubricated and winds fully. The mainspring might just be very weak. 

It's a bit of a mystery why it doesn't run. The impulse jewel is between the banking pins and the regulating mechanism doesn't seem to be the problem.

Either there is too much friction somewhere - I have no idea where - or the mainspring just isn't strong enough to keep it running.

I find it strange that it runs when I keep winding pressure on the mainspring.

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m1ks WRT Addict

m1ks

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My guess would be friction on the barrel arbor pivots or a weak mainspring. I know the symptoms you mention, I have an HMT that exhibited those and winding fully would get the balance moving lethargically briefly then stop. Then holding winding tension got it swinging and it eventually continued but the amplitude is low. That will get stripped, cleaned and checked at some point.

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nickelsilver Distinguished Member

nickelsilver

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It's about 99.99% not a mainspring issue. It should limp along with a 5x weaker spring- poorly but running. Is the train free with the balance and fork out? Like two clicks of wind, train should run and escape wheel should turn backwards at least a little at the end. With just a few clicks of wind the fork should snap back and forth cleanly. With fork out and balance in, balance should oscillate freely and for quite some seconds with a swift twist of the movement. If these things aren't happening then start checking methodically.

Going back to the barrel- it could be an issue: when you assemble it you should hold the assembled barrel between stout tweezers on the ends of the arbor and check for endshake. Make sure the cap is fully seated. Make sure the holes in the plate aren't too worn (often an issue with seiko). But even if all that was wonky it should 'run', at least poorly, with a couple of turns of wind.

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StuartBaker104 Distinguished Member

StuartBaker104

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It can be very difficult to observe the effects of wear in the barrel arbor bushes. This can cause the barrel to cant over and significantly increase the friction in driving the next wheel in the train.  This will not happen without tension in the spring, but you can see how much play there is when the spring is unwound.  Wear could be in the barrel or the movement plate/barrel bridge.  In the latter case you sometimes have to look at the plates from the inside as the wear can be below the edge of the oil sink.

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Folkvisor Super WRT Addict

Folkvisor

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6 hours ago, yankeedog said:

Agreed.with the balance and pallet assembly removed the watch should spin.even with a weak mainspring.

It does. I've removed the balance and the pallet fork and it spins with no problem with only one turn of the crown.

The pallet moves back and forth and the balance is free. I'll check the barrel for wear.

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nickelsilver Distinguished Member

nickelsilver

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8 hours ago, Folkvisor said:

It does. I've removed the balance and the pallet fork and it spins with no problem with only one turn of the crown.

The pallet moves back and forth and the balance is free. I'll check the barrel for wear.

One turn of the crown or one click of the ratchet wheel? It should spin the gear train with one or two clicks. With a few clicks the fork should snap back and forth with a little nudge.

But imagining one turn of the crown turns the train the watch should still run. If it's even just close to being in beat, the balance is free, the fork is working correctly*, and the train is free, the watch really should run with just a bit of winding.

Check with balance and fork in, power down, see that the balance swings freely while engaging the fork. It may stutter a bit as the fork knocks into the escape wheel, that's normal.

 

*Perhaps the escapement is grossly out of adjustment but still "snaps" when manually advanced.

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Folkvisor Super WRT Addict

Folkvisor

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Thank you both for your input.

I will check the hairspring again. It was messed up and I had to untangle it but it was flat, evenly spaced and centred on the balance cock before I put it back on the balance staff. I'll check it again but i really hope it's OK. Working on it under a microscope with fine tweezers isn't my favourite thing to do. 

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Folkvisor Super WRT Addict

Folkvisor

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18 hours ago, yankeedog said:

Brain surgery is probably easier.

Funny you should say that. I was on a watch factory tour and one of the companies held a master class in watchmaking for us. The guy next to me had been a brain surgeon and he was losing screws left and right. He turned to me and said, “I’m sure glad my former patients aren’t watching me do this.

 I’m not at home just now so I’ll let you know what happens.

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