I have just attempted to replace a broken regulator spring off of a 990, with a spring from a 974. They looked the same, but when I removed them to make the exchange there is a problem. As you can see the one on the left is the broken one and there is a small hole next to the screw hole that a little pin from the regulator cock goes into to help hold it in place. The one on the right has a little pin to apparently fit into a hole that is being occupied by a little pin.

My question: Are there two different regulator spring designs, or, is the pin stuck in the hole? If there are two designs where could one be found?

And save the pin and the "old" regulator screw!

Thanks, that is the information I needed, but how does one remove the locator pin without damaging the balance bridge? Very small needlenose pliers?

If you have an ultrasonic cleaner it might help to loosen the pin.

I used a tweezer and some fluid and it eventually rocked out. As for the tiny extra screw, well, it's somewhere!

I got my $12 worth today!

I would tighten a pin vice around the pin, or better yet a wire chuck of the proper size in the headstock of a watchmakers lathe, and while holding the headstock slowly move the balance cock back and forth and gradually pull out the pin.

Larry

Mike,
Try and find that screw. You'll be needing one someday.

Actually I did find it later. And I saved it. They really are small and hard to work with. The watch looks much nicer with the regulator spring correctly installed and unbroken.