1937 Elgin Grade 315 Running Slow

[gpraceman]

My father-in-law handed me a 1937 Elgin Grade 315 pocket watch to fix that had belonged to his father.  I have it running again, but it is losing about 160 seconds per day, regardless of the position.  That's with it regulated to the faster limit.

I replaced the mainspring with NOS Elgin 2339.  Blued steel, not white alloy.  It is an S-shaped mainspring.  Old mainspring was essentially cemented in place with dried oil so I didn't want to reuse it.

It had a broken balance staff.  Caseback has a dent in it, so the watch took a good shock.  I was able to find a donor movement from the same manufacturing year and swapped out the balance wheel and hairspring.  I know that the ideal solution is to replace the balance staff, but I'm still pretty new to this.  I am looking for a staking set and will eventually tackle that repair.

I was able to get it back running with the donor balance.  Amplitude was about 270 deg and beat error 0.3 ms.

There are no timing washers on the balance wheel, that I can tell.  No meantime screws.  The hairspring is between the regulating pins.  I did not lubricate the pallet fork pivots and just a tad of Moebius 9415 on the face of the pallet jewels.

I took it back apart to reinspect and reclean it.  I found a chipped jewel for the seconds wheel on the mainplate.  Would this really be my culprit?  I would have thought that I would see some obvious positional error, especially in the dial down position.  Pivots look fine.  All other jewels look fine.

[JohnR725]

7 hours ago, gpraceman said:

balance wheel and hairspring

By swapping of the balance complete you do not know the history of that balance complete in other words what makes you think it's supposed to keep time? Versus the original one where the owner or somebody might've said yes it was fast or slow.

7 hours ago, gpraceman said:

I found a chipped jewel for the seconds wheel on the mainplate.  Would this really be my culprit? 

If you look at American pocket watch jewels you always find that ship a flaw or something their vintage natural stones. Yours looks just fine

Then is your balance wheel perfectly round? The bimetallic balance wheel has arms that can move especially if somebody squeezes them typically that will run fast. If for some reason their bent out just a hair you'll run slow.

 

[gpraceman]

21 minutes ago, JohnR725 said:

By swapping of the balance complete you do not know the history of that balance complete in other words what makes you think it's supposed to keep time? Versus the original one where the owner or somebody might've said yes it was fast or slow.

If you look at American pocket watch jewels you always find that ship a flaw or something their vintage natural stones. Yours looks just fine

Then is your balance wheel perfectly round? The bimetallic balance wheel has arms that can move especially if somebody squeezes them typically that will run fast. If for some reason their bent out just a hair you'll run slow.

 

Yes, I know that swapping in the balance wheel and hairspring for a donor is not a perfect solution, that they had tuned these for the particular pocket watch they originally went in.  I did keep the original balance cock, to reduce the amount of change.  It was rather the more expedient way to get the watch running again until I can get a staking set and some experience under my belt before attempting that repair on a family heirloom.

I hadn't noticed any out of round with the balance wheel.  Once I get it back together, I'll check that out.

I would think that the chip being on the edge of the pivot hole would be a problem, but maybe far less of an issue than the balance change.

[JohnR725]

4 minutes ago, gpraceman said:

I would think that the chip being on the edge of the pivot hole would be a problem, but maybe far less of an issue than the balance change.

You can look at the wheel with its pivot that goes into the offending jewel and do you see any signs of damage? Then replacing the jewel is always a interesting thing at least it's on the dial side you can use a modern jewel nobody's going to notice it just depends on how you want to do this.

Oh and the regulator pins how far apart are they?

7 minutes ago, gpraceman said:

I did keep the original balance cock,

On American pocket watches you will find a serial number very visible. But underneath every single plate will be a partial of that serial number. It's because when they were making the watch all the parts were made together. So in general you really can't swap bridge components for the most part because they just won't fit. There is a reason they put serial numbers on everything to keep everything together.

11 minutes ago, gpraceman said:

that they had tuned these for the particular pocket watch they originally went in. 

For timing the balance wheel and hairspring were matched together so as long as you keep the hairspring with the balance wheel timing should be fine. The problem becomes the escapement adjustments can have issues when you're swapping balance completes sometimes some of the components will have slightly different sizes.

[gpraceman]

1 hour ago, JohnR725 said:

You can look at the wheel with its pivot that goes into the offending jewel and do you see any signs of damage? Then replacing the jewel is always a interesting thing at least it's on the dial side you can use a modern jewel nobody's going to notice it just depends on how you want to do this.

No sign of damage on the wheel or pivot.  Probably a non-issue, due to the pinion that would contact that jewel.  The face of that is pretty wide and flat with respect to that jewel.

1 hour ago, JohnR725 said:

Oh and the regulator pins how far apart are they?

Now that you mention it, I did have to widen those a bit to get it to release the old hairspring.  The gap really didn't seem too bad.  When I get it back together, I'll adjust that.

1 hour ago, JohnR725 said:

On American pocket watches you will find a serial number very visible. But underneath every single plate will be a partial of that serial number. It's because when they were making the watch all the parts were made together. So in general you really can't swap bridge components for the most part because they just won't fit. There is a reason they put serial numbers on everything to keep everything together.

Yes, I know about the matching serial numbers.  I did want to keep this pocket watch as original as I could, so another reason to keep the original balance cock.

I did think it a bit strange that the train wheel bridge on the donor movement indicated that it was 17 jewels (eBay listing photos), when it should have been 15 jewels.  Once I had it in hand I could see from the serial number for that bridge that it was not original to that pocket watch.  All other serial numbers matched though.

1 hour ago, JohnR725 said:

For timing the balance wheel and hairspring were matched together so as long as you keep the hairspring with the balance wheel timing should be fine. The problem becomes the escapement adjustments can have issues when you're swapping balance completes sometimes some of the components will have slightly different sizes.

Gotcha.  It may have to remain running that way until I can replace the staff in the original balance wheel and restore it to the pocket watch.  Unless there is some easy adjustment that I can make to it.  In reality, my father-in-law is not going to be depending on it as a timepiece.  It will be sitting in a glass display dome along with some other stuff of his father's.  I was just looking to get it running as good as I could.

Edited September 18, 2023 by gpraceman

[JohnR725]

4 minutes ago, gpraceman said:

The gap really didn't seem too bad.

Over coil hairsprings have to have the regulator pins as tight as possible but still allow the hairspring to slide. Then ideally they hairspring should build the slide in for reassembly. Otherwise if they're far apart that would be a reason for running slow especially as the amplitude drops.

 

6 minutes ago, gpraceman said:

It may have to remain running that way until I can replace the staff

Just keep the original balance wheel with the watch and don't worry about it.. It only really become an issue if the replacement balance wheel wasn't working properly at least as soon as you deal with your timing issue.