Well, I'm venturing into wristwatches... Have a Gruen Precision 17J Autowind, Swiss movement, appears to have a broken mainspring. Numbers on the movement include F1560 by the escape wheel, GXC on the base of the balance cock, and 550SS on the autowind weight.

Any ideas on a part number of a mainspring?

Mike Miller
NAWCC Member# 154831
NAWCC-IHC Charter Member# 27

According to my Bestfit catalog, the mainspring should be a White-a-loy #WA40 or an A40 Samson. This is for a MS that has Dennison dimensions of 5 1/2 x 10 x 12 1/2. I hope that this helps.
B

Mike,

You did not describe exactly what you're experiencing. Usually the mainspring in automatic self winders do not break. I would like for you to post a description of how it was determined the mainspring is broken. Please bear in mind that self winding watches when fully wound are designed to slip In other words on most of them you can wind until the cows come home and never come to an end like on a wind up watch.

This is accomplished by having additional length of mainspring attached to the end of the mainspring curving in the opposite arc. This produces drag against the mainspring barrel allowing a specific amount of wind before slipping.

Having said all of that if the mainspring is in fact broken any supply house can get you the spring using manufacture name and line size or model number in this case 550SS.

Hope this helps,

Rich Kuhn

NAWCC Member 128623
IHC Member 155

rich_kuhn@email.msn.com

Thanks for the replies,

Richard, I haven't determined exactly that it is the mainspring that is the problem. I am familiar with the slip arrangement in the spring design. While wearing the watch the other day, there was a "pop" and the watch stopped. Initial examination indicates that all is ok with the train, balance and escapement. There is simply no power to the train. I will be tearing it down soon and thought I'd order a mainspring ahead of time banking on that being the culprit. If there are any other ideas as to what problems to look for, I'd be most appreciative in hearing them.

Mike Miller
NAWCC Member# 154831
NAWCC-IHC Charter Member# 27

Mike,

Could be the mainspring barrel opened and released the spring, perhaps that might be the "pop" you heard. This is not a simple arrangement and not at all the kind of watch I'd recommend as a first project.

Be VERY careful in taking this apart, be absolutely certain it has been let down before you remove the bridge which contains the mainspring barrel. However, prior to that it is necessary to remove the self-wind mechanism. And that is where you can get into a LOT of trouble.

Let me put it this way, in watchmaking school one had to first be entirely proficient in "time-only" movements prior to working with movements of greater complications. If you'd like some guidance on this or any other procedure feel free to call me at 440-878-9385 afternoons or evenings but not after 10:00 Eastern Time.

Regards,

Rich Kuhn

NAWCC Member 128623
IHC Member 155

rich_kuhn@email.msn.com

Richard,

Your words of caution are heard loud and clear. I must admit, this one is is a little like driving beyond my headlights. I have done a lot with pocketwatches, down to 0 size. But these wristies are a different beast. The autowind mechanism looks to be an aditional bridge atop a standard movement. and those clicks look tiny

I will proceede with caution and appreciate your offer of guidance! Might be taking you up on it real soon

Mike Miller
NAWCC Member# 154831
NAWCC-IHC Charter Member# 27

Mike,
You picked quite a "beastie" to cut your first "Wristie" teeth on. I've studied the self wind topic heavily with Rich and he is right when he says understand the plain time onlys first. Once you get past the autowind unit, what sits underneath will start looking familier to you. The urge to tear down the auto wind unit like you would a regular pocket or wrist movement got the best of me in my first experience. Those little "clicks" and their stinky little springs like to fly. After a good hour of "minesweeping my room with a magnet recovering everything (I hoped), the real challenge arrived....how does this go back together. To this day I make a sketch of the little spring and click arrangements before I loosen the first screw. In most cases the whole "gizmo" can be lifted off intact when you determine the right screws to remove. Excercise caution with "Gruen"...they're notoriously "flimsy" in nature.
Good Luck

Ralph Rehner
NAWCC# 151536
IHC Member# 149

I finally decided to give it a try, The watch is nothing special and I do want to learn. I have examined the autowind mechanism and am past it for the most part but would like some advice on where to go next in the dismantle.

A little update first. The mainspring is not the problem! It opperates and slips like it is supposed to. My suspicion is that the train is gummed up and simply won't transfer power to the escape wheel, or there is a spec of dirt lodged in a gear. Beleive it or not, a local watchmaker (AWI certified) did a cleaning on this one 4 months ago, but the plates and movement have a sticky film throughout (lube solution?)

If you look at the photo you see that the autowind works are removed. Mainspring tension is down. The lever bridge would be my next step, Along with the cannon pinion on the reverse side, And it looks like the barel and train bridge are combined and held with 4 screws. What about the small bridge with three screws at the back of the center wheel? Should this come off before the barrel/train bridge?

Any pointers greatly appreciated.

Mike Miller
NAWCC Member# 154831
NAWCC-IHC Charter Member# 27