Reply To: Fine tuning

[Bob Tascione]

Sgoodstal,

Since the balance amplitude is good and balance motion recovery time is quick I think your timing problem does have to do with the balance assembly.
When you say that you changed the spring I’m assuming that you are referring to the mainspring and not hairspring. It is possible though that the hairspring may have been changed sometime in the past. The fact that the mean time screws were already turned up against the balance rim could mean that someone in the past had to deal with this slow rate problem. You mentioned in your first post that you didn’t think this watch has mean time screws. You may be correct as I don’t have a 992 here to check out but I was under the impression that the 992 split balance has 2 mean time screws and the 992E (elinvar) solid rim has 4. I’ll have to do a little digging through some books to find out.
Because of the extreme positional error it’s very possible that the balance is way out of poise. Here are a few things you can check.

1. Check the balance in a truing caliper to determine that it’s true in the flat as well as in the round. It’s very possible that the staffing process has somehow distorted or stretched the balance arms. This can result in the rate problem you’re seeing.

2. Check that the staff is securely staked to the balance. A loosely staked staff is a fairly common problem.

3. Check for concentricity (If the staff is staked off center).

4. Check that the roller table is secure on the staff.

5. CHECK that the ROLLER JEWEL is not loose. VERY COMMON problem. Also check that the roller jewel is straight and not jamming in the pallet horn.

6. Make sure that the hairspring stud is tight in the balance cock hole and that the regulator pins and regulator are secure.

7. Check that all balance rim screws on one arm of the balance match the screw location of screws on the other arm. Same hole pattern beginning from balance arm to end of each rim.

8. Check that all balance screws (not the mean time screws) are turned and tightened down to the rim.

9. Check the poise of the balance.

10. Cracked, shattered or loose balance hole and cap jewels.

Let us know how it goes.
Hope this helps,
Bob