7750 Ratchet drive wheel repair

[gasdoc 0]

I felt guilty about not having any quality posts (I'm mostly a lurker) so I pulled out this old post from 2009 I did on another forum. It may help someone....

 

The BCE (28.8k asian 7750) I bought for a friend about 7 months ago kept stopping. The watch would come to life with gentle swirling to charge the rotor, or with handwind but would stop soon after.

 

I posted this one previously, but here is the solution. (My solution anyway)

 

DISCLAIMER:

I am not a watchmaker or expert. I decided to undertake this experiment since without it, the movement would be junk. Please don't try this unless you like your movement to be junk. This is for entertainment only.

 

 

The Ratchet Drive wheel had several teeth knocked off. I'm not sure how this happened exactly, but I've been told this is a result of aggressive hand winding the 7750 along with poor lubrication or a dirty movement. I ordered a replacement ETA wheel from Borel hoping that it was a direct swap. Careful that you get the ratchet driving wheel, the ratchet wheel itself is sturdier and steel looking.

 

Sorry for the crap pictures.

 

The wheel on the right is the asian with the missing teeth, the left is the ETA.

 

Well, no luck, the jewel bearing is smaller on the asian for this part, can't interchange it.

 

So now I have a useless movement, and a perfect new ratchet drive wheel that won't fit.

 

You can see that the wheels construction is a steel pin pressed into a brass? gear wheel.

 

So here is what I did:

 

1. I drilled a hole about 2mm in diameter into my aluminum movement holder, deep enough that the entire center pin could fit into it.

 

 

2. Place your ratchet wheel, small gear side down into the hole.

 

 

3. Slowly close the movement holder using the adjustment bolt (black) until the opposite side it touching the ratchet wheels pin. Then apply gentle pressure making sure everything is level.

 

 

4. TADA! You've removed the pin.

 

 

5. Now without mixing up all the parts, repeat on the ETA wheel.

 

6. Take the center of the asian ratchet drive wheel and the outer brass gear of the ETA wheel and set aside.

 

7. Drill a hole in the aluminum movement holder the size of the shoulder of the center pin from the wheel and put it in the hole as shown.

 

 

 

8. Now drop the ETA brass wheel onto the asian center pin, and carefully line the holes up. I used a little grease to hold all the parts steady.

 

 

9. Drill another hole directly opposite the 1st tiny hole so the pin can go inside the aluminum while it presses down the brass wheel. Slowly and carefully close the movement holder down so it presses the wheel on.

 

PRESTO! You've got a servicable ratchet drive wheel.

 

Now I know this probably isn't the best way, and I am sure someone will figure out a better one, and a better press might help too, but in a pinch it worked great.

 

Other options?

1. Replace the jewel bearings with ETA versions? Not sure how or what the cost would be.

2. Grind down the center pin on the ETA wheel to fit the asian jewel bearing....seems almost impossible.

 

 

Completed asian/swiss hybrid ratchet driving wheel installed.

 

Swiss 7750 reversing wheel installed (direct swap - some movements only). These go bad commonly on the asian, see Fransisco's writeup on this one.

$15.50 from Borel.

 

Hope this helps someone, or inspires them to find a better way. We will see how long it will last.

[10:10 Watch Repair 1]

nice work and DIY solution.

Every watchmakers bench should have a staking kit BTW, which is designed for this sort of work.

[Luthier 1]

I'd use Dremel as a lathe, and carefully thin down the pin's end.

But you found great solution already, Mike.

[gasdoc 0]

the pin end is so tiny this would probably not work. I know somepeople can do it with a watchmakers lathe, but still tough.

[MikeMcNair 0]

very very well done sir!!!!!!!