Medana MST 377 with "rocket bar"

[luiazazrambo]

Hello *,

I have a Medana watch with a broken mainspring, with a missing mainplate screw and I could not pull the stem out into hand set position. I was thinking that probably I dont have the right stem installed. Found the movement which is an SST 377 on ranfft, and I found the stem on flume , but it does not say dimensions. Ranfft under the "remarks" says that the movement has "crown mechanism with rocker bar" though. What does that mean? What is a "rocket bar"?

The crown with the stem I have:

Any comment is appreciated as always.

Take care,

lui

[watchweasol]

Hi I think it is rocker bar refering to the rocking gear ass when the stem is pulled out the bar moves to engage the hand set grears.

[StuartBaker104]

This is the rocker bar

If the stem is correct and installed correctly, then the peg on the set lever (just above the rocker bar in the picture) should sit in the slot in the stem.

When you pull the stem to hand set position, the set lever should rotate clockwise and the right hand end of it should engage with the cam shape on the top RH corner of the rocker bar, causing the rocker bar to rotate clockwise until the end of the set lever hits the stop in the rocker bar.

The parts all need to move freely for this to work properly, so could be a lubrication issue.

The rocker bar has 3 meshing gears on it - the centre one turns when you turn the stem, causing the other two to turn. In winding position, the one on the left winds the mainspring. In hand setting position, the one on the right turns the minute wheel.

With wear or damage, any of this could jam up when you try to move it.

Photos of yours might show where the problem is.

[StuartBaker104]

Oh, and here are the stem dimensions...

[luiazazrambo]

3 hours ago, StuartBaker104 said:

Photos of yours might show where the problem is.

Thanks a lot for this description, good to know that this rocket cannot be used to travel to Mars.  Why is it called rocket bar? The movement is stripped down at the moment as it was not possible to wind up, turned out that it had a broken mainspring. I am going to clean the movement, replace the mainspring (once I get one), the one I got with the watch (not sure if original or replaced over time, it is bluesteel ) is 290 mm long, ranfft says 240mm (1.70 x 9.0 x 0.12 x 240mm) Cousins has 280 mm or 300 mm and lubricate it. Then I am going to try it out once again and post a picture of it.

[AndyHull]

On 4/7/2020 at 11:58 PM, luiazazrambo said:

Ranfft under the "remarks" says that the movement has "crown mechanism with rocker bar" though. What does that mean? What is a "rocket bar"?

Rocket? Rocker surely, though rocket sounds like more fun.

Edited April 8, 2020 by AndyHull

[luiazazrambo]

Khmmm..... 

 

[StuartBaker104]

Yes, definitely rocker, not rocket. Anyway, no travel to Mars permitted during lock down!!

GR catalogue lists the mainspring for this movement as 1.7 x 0.105 x 300 (GR4895). This is obsolete, and the nearest would be GR4894 which is 1.7 x 0.105 x 280.  Ranfft spring recommendation is much thicker and you may run into trouble with that.

[Redwood]

I bet if you can’t fix it it will be on its way to Mars  

[HSL]

If you don't find  the right GS The Bestfit number for this one is.
MST 377    200/638F         BESTFIT STEM
MST 377    200/644F         BESTFIT STEM
It seems it the same stem for the most of theese in the movement family.

Compatible CaseCaliber
MST 308
MST 309
MST 312
MST 320
MST 321
MST 322
MST 323
MST 353
MST 355
MST 359
MST 360
MST 365
MST 368
MST 374
MST 375
MST 377
MST 379
MST 384
MST 385
MST 393
MST 394
MST 403
MST 404

And you could get them on ebay...
https://www.ebay.com/itm/Winding-stem-Albero-di-carica-tige-NOS-MST-344-345-360-374-375-377-379-384-385/162039052101?hash=item25ba47b745:g:zigAAOSwL0NXEKhc

[luiazazrambo]

On 4/9/2020 at 12:32 PM, Redwood said:

I bet if you can’t fix it it will be on its way to Mars  

I might be able to use this movement, my 5 years old daughter told me 2 days ago, that she wants to be an astrophysicist. I am going to lend his movement to her when she goes for hands on trainings.    

[luiazazrambo]

To my surprise I had the stem in stock, ordered a mainspring from cousins, but I broke the pivot of the pallets when I tried to put it together.  I heard it snap, what a horror!!! Waiting for new pallets to come. Also found a barrel bridge screw  (not mainplate as I stated earlier) in the proper size and shape after checking hundreds of screws with my microscope. The proper stem does not share the same dimensions with the one the watch came with. It must be the reason why I still cannot pull it in hand set position, I have not tried it yet, but i can move the set lever with my tweezers relatively easily. All cleaned and lubricated so far, but not completed. Will post the end result once i am done.

Edited May 27, 2020 by luiazazrambo
as usual, correcting English

[luiazazrambo]

Could you please help me with the crown? I have these buttons, but what does that 9/24, 9/28 etc means? 9 or 8 are the thread size right? 9 is 0.9mm? But what is /24 and /28 and /30? Would that be 2.4 2.8  and 3 mm? I tried to compare a 9/24 to a 9/30 but the 9/30 does not seem to be bigger in any dimension? Not even sure if the right sized buttons are in the right container. I am trying to find a silver button for the silver case. Would be nice to know how the original looked like.