Leica IIIF - any ideas?

[Twotone]

Hi folks,

I'm in the process of learning how to undertake a full rebuild and service of IIIF bodies.
It's all going well and have accumulated some excellent resources from some very helpful people, however I've been unable to understand the cause/solution of a particular issue.

I have a very clean but slow IIIF Red Dial which I plan on doing a full rebuild of soon, in the mean time I have a rough IIIF Black Dial which has curtain pinholes, rust etc (which actually is running very well!)

The latter is the one I've been disassembling and reassembling regularly and learning with, however it already had an issue that I've not yet figured out how to remedy.

I have included 2 pictures, one of the 'bad' example which is the black dial with this issue, and then a reference photo of the 'good' example which is the nice IIIF red dial I have.

The 1st Curtain cam and latch (pawl) aren't fully engaged with each other - they engage just enough but it's not right and I'm not happy with it.
At first, I thought the spring (circled in the attached image of the 'bad' example) was the cause, and whilst it is a bit beat up, I verified it was not the cause by swapping the spring out temporarily from the 'good' body. I then proceeded to also swap over the cam and pawl from the good body, however none of that has cured the issue. If you push the pawl into the cam notch it will go in but it won't repeat the same amount of engagement without physically pushing it in. I have also verified it presents the same (not engaging enough) with the flat release spring removed.

Someone else suggested it may be a curtain issue, I don't have anything else to go off currently.
Does anyone have experience of the solution to this? I'm expecting I'd find the answer or resolve it when I remove the curtains and rollers and replace the curtains but just curious to hear anyone's thoughts on it.

Thanks!
TT

 

[Nicholas Lindan]

If you push the pawl will it fall into the notch in the cam/wheel?

If it is not pushable, what is standing in the way of the pawl's free movement?

If it is pushable it is probably a dynamic issue - the pawl isn't able to move fast enough to fully engage in the notch. Most likely culprits are wrong/dried lubricant, over-tightened screw or missing washer. You seem to have ruled out the spring as being the culprit - I take it the different angle of the spring it due to the differing pawl engagement.

 

[Twotone]

If you push the pawl will it fall into the notch in the cam/wheel?

If it is not pushable, what is standing in the way of the pawl's free movement?

If it is pushable it is probably a dynamic issue - the pawl isn't able to move fast enough to fully engage in the notch. Most likely culprits are wrong/dried lubricant, over-tightened screw or missing washer. You seem to have ruled out the spring as being the culprit - I take it the different angle of the spring it due to the differing pawl engagement.

Hi Nicholas,

The pawl will push into the notch, but requires a reasonable effort push. I've tried playing with the locking pawl profile slightly too to rule that out but that made no difference.

The spring is a slightly different angle due to the pawl engagement as you correctly pointed out.

The pawl itself moves freely, I've verified there shouldn't be a washer underneath (checked the technical drawings and compared the other IIIF I have) and also confirmed the screw is not overtightened. If anything I suspect it to be something gunked up as you say - on further inspection I think there is a very slight difference between the point the cam finishes rotating on this one vs the 'good' IIIF I have, so if that's the case I need to figure out why (or perhaps it'll be something that will end up resolving itself when I replace the curtains etc.

Thanks