Leica IIIg loose speed selector dial

[SyPat]

Although the speed selector dial (high speeds) of my IIIg is firmly screwed on his axis, it slightly turns each time I take a picture. If I select the 'right' 1/125 and take a shot, after rearm, the mark on the hot shoe will be in front of 1/500, next time it will be betwwen 1/1000 and "B" and son on.
As far as I understand, the problem comes form the axis itself. How could I fix it ? any idea ?

 

[02Pilot]

The high speed selector is secured to the unthreaded shaft with three grub screws, so I'm assuming you mean that these are tight. The screws should be pointed to grip the metal of the shaft firmly. Either they are rounded off, or the metal of the shaft is worn away (this should be obvious, as it would be a bright groove), or the screws aren't really tight, but the threads are dirty making it feel like they are. I would first remove the knob, clean and inspect the shaft, and apply some Ronsonol to the screws while gently working them back and forth in their holes (best not to remove them if you don't have to). This should clean up the threads to some extent and give you an idea of if there are any obstructions or points where things start to tighten up.

 

[Spavinaw]

I had this same trouble with a Leica IIIf many years ago, so my memory of it is a bit hazy. As I recall the speed dial does not grip the shaft directly. There is what I'll call a "fat washer" on the shaft held in place by set screws. Then the speed dial is held to the fat washer, also by set screws. It was the set screws on the fat washer that were loose, not those on the speed dial. I don't know if the IIIg is like this or not. Good luck.

 

[davidnewtonguitars]

+1 on cleaning and lightly lubricating the threads of the grub screws.

Also, upon tightening them, be sure to limit the torque to less than what will strip off the straight-slot of the screws. Nothing feels more like "mechanic's failure" than the surety that the screws are well-set, and the falling out of little pieces of metal that are the sheared-off screw tops.

 

[SyPat]

Thanks to all.
According to this schema:
http://www.rangefinderforum.com/forums/attachment.php?attachmentid=106200&stc=1&d=1498007033
the problem came from the screws "531-231". Now, it's fixed.