I wouldn't advise any filing of components. Ideally the keyless works should be fully dismantled, cleaned and lubricated. The first thing you could try is to apply some suitable grease on the contact areas circled on the pic.

 

I hesitated to post about lubrication thinking that we might have passed that already with the mention of files.

A thick grease on those points would be good.

 

Thank you, but I've done that already. It looks like there is too much tension in the stem of the spring; it's a little curved (see yellow part). I will disassemble these part again and replace them.

 

Ah, right. Personally, I don't think there looks to be too much tension in that spring. It needs to be under tension so that it drops down when the crown is pulled out. The main resistance when pulling out the crown will come from the circled contact area in the following pic:

So if I had your issue, I would concentrate on these surfaces, making sure they are nice and smooth, possibly polishing, not sanding the surfaces with a very very fine grit wet and dry followed with some thicker grease.

 

Just something else to check that I've noticed in the picture, is the yoke screw correctly aligned with the hole in the yoke and the yoke moving freely. Is the screw pinching the yoke as it doesn't look central?

 

I agree with @SQ-whiff , I think you should look at the yoke lever and check it is moving freely also that the castle wheel slides easily on the stem The setting lever spring shouldn’t create that much tension to affect things that much. I’m with sq-whiff on this one 👍🏻

 

Agree, looks like the screw probably has a shoulder which is sitting on top of the yoke rather than centered within it.

 

Waaoouuhh, I wasn't expecting so many answers! Many thanks to all of you . I've disassembled / reassembled those parts, and also flattened slightly the yoke spring, which was very hard, lubricated the whole thing, and it's far better now. Here is a picture of the watch which was made in 1937
Thanks again!

 

Very nice.

 

Lovely watch 👍