Jaeger Le-Coultre P478 balance jewels

[Barnaby]

I've just finished servicing a JLC P478.

When I got the watch it was missing the top balance jewels (endstone and cap). I ordered what I thought was the right jewels from Cousins, but what arrived was a jewel in a big brass setting with two screw holes, as if for non-shock proof movement.

So I decided to try swapping in jewels from other movements to see if any would work. I tried jewels that matched the diameter of the bottom balance jewels of the JLC- like the Seiko 6119, or Incablocs fro ETA movements, but they were the wrong depth. I ended up with the jewels from a FHF 905. They had a slightly smaller diameter than the JLC ones but they fitted depth-wise perfectly, and the watch ran.

But....the watch runs very well in all positions except for two of the vertical positions. I'm talking 290 degrees DU, DD, CD, CL, dropping to 150 degrees CU and CR.

So the first question is: could ill-fitting jewels on one end of the balance cause this?

If yes, then it would be good to get the correct jewels. I'm not familiar with JLC movements, so if anyone knows what the correct ones are then that would be great.

[nickelsilver]

They would probably (pretty much 100%) be Kif jewels, and probably show issue du dd, not two vertical positions if wrong. Likely they aren't correctly centered, causing interference with the fork in those positions.

[nevenbekriev]

OK, but You should first say if th the radial and axial free play of the balance is OK with the new setting, does the balance not rubb in anything around... Sometimes, when radial free play has got for a reason slightly bigger, then in the vertical position where the balance is above the fork, as it gets closer to the fork, the impulse jewel rubbs in the fork arches. In such case, slightly bending the banking pins out helps. This is espacially true for hi grade moveements, where all gaps and free plays are adjusted to minimum.

[Barnaby]

It seems that the best thing would be to source the correct Kif jewels. I've checked the Cousins website and find the Kif section totally confusing. The endstone needs to be 1.5mm diameter and the cap jewel is 1.2mm diameter. On their website there's Kif 501 through Kif 584 endstones...

[nickelsilver]

Cousins has this list of Kif parts for LeCoultre, looks like for 478 the cap jewel (contre pivot) is part 516, and the hole jewel (chaton empierre') is 303 / 9.2. The 9.2 is the hole size, or 0.092mm. A 0.09mm should be fine. Both are in stock at Cousins.

[Barnaby]

That's brilliant, thank you so much

[Barnaby]

I've fitted the new jewels and the issue persists...

Looking at this:

On 6/10/2024 at 7:02 AM, nevenbekriev said:

OK, but You should first say if th the radial and axial free play of the balance is OK with the new setting, does the balance not rubb in anything around... Sometimes, when radial free play has got for a reason slightly bigger, then in the vertical position where the balance is above the fork, as it gets closer to the fork, the impulse jewel rubbs in the fork arches. In such case, slightly bending the banking pins out helps. This is espacially true for hi grade moveements, where all gaps and free plays are adjusted to minimum.

i cannot feel or notice much side-shake at all. But the bad position is the one in which the balance is over the fork. The banking pins are already bent outwards about 10-15 degrees...

[nevenbekriev]

On 6/20/2024 at 4:05 PM, Barnaby said:

But the bad position is the one in which the balance is over the fork. The banking pins are already bent outwards about 10-15 degrees...

Well, if they are already bent (probably in the factory), does it mean that bending them more will cause something awfull?

I would check if there is 'healthy' free play between the guard finger and the guard roller on both sides and between imulse jewel and fork horns too. This will make things clear and will help to make the right decision what to do in order to solve the problem.