I bought a brilliantly clean SB 209 movement off of E-bay for next to nothing that the seller said needed a balance staff. When I removed the balance assembly for staffing, I noticed the balance cock had two dial spacers wedged under it. I re-staffed the watch, re-assembled it, and holding the balance cock in place with my fingers checked the running of the movement. It ran fine. Then, when I began to tighten down the balance cock screw, the balance froze. If I loosen the balance cock screw, it begins to run again. As long as I don't tighten the balance cock screw, it runs fine. Just one or two turns of the screw and it freezes. Any thoughts on this? Thank you in advance.

Robert,

To answer this correctly would be a very lengthy answer, if we assume the problem lies with the staff and you have the 100% correct staff for the model, you may need to adjust the staff length slightly and polish pinion and tip once done, examine carefully which end or both to make the adjustment and of course making sure there is sufficient length to remove without encroaching on the cone section when endshake and gravity taken into account.
There are many other causes and tests that should considered, this is really where you need to sit with someone and examine. Of course we are assuming that the jewels are 100% and seated, often people will grind them away, change incorrectly, check for quick fix gouging of underside of cock and plate, bending of balance cock itself and anything else that may look odd often you have to try and undo many previous quick fixes.

Thank you for your reply, Mr. Abell. Maybe I should just send the thing to you!!!!
Thanks again,
Robert

If you still have problems send it over and will take a look.

It's on the way today, Mr. Abell. Let me know what you find. Thanks.