Zorki-4k rear light-baffle question.

[Grytpype]

I have two Zorki-4Ks, both purchased with sluggish 2nd curtains. I'm CLA-ing one now and stripping it to a bare crate first. The baffle-plate at the back that fits just in front of the curtains has 2 strips of 'velvet' type light seal material glued on, and when I removed it it was clear that the 2nd curtain had been rubbing on the strips quite heavily, which seems to me like A Bad Thing.

The mounting holes in the baffle-plate are enlarged, obviously to allow adjustment. Am I right in thinking that the plate should be set up so that the strips are just not quite touching the curtain? Is any clearance allowable, or would this cause light leaks?

I'm betting this was the prime cause of the problem. With the baffle-plate removed the 2nd curtain runs very freely at the lightest tension. When I get to the second camera I will check this baffle-plate first!

Steve.

 

[fidget]

Those shields do need to be set up fairly accurately.
I've had a few cams where they allowed too large a gap. This in turn allowed the curtain laths to separate when rewinding and letting light onto the film. Once you've recognised the pattern it leaves on the negs, you can sometimes see the same problem in other posters problem pics.
When the shutter is released, the curtain laths travel behind the shield one by one. The clearance here will be obvious and not critical.
When being cocked, the two laths are dragged back whilst they overlap, so this is what dictates the gap. Too tight here and the rewind will be stiff or even start to jam. Too much gap and light can get between the laths.
The older cams did not have any felt on the inside of the shields, whereas later cams (or particularly Zorkis maybe) had some material here. It seems like a good idea as a soft compressible material lining the shields would give a small spring like effect on the cocking laths and so help to maintain a nice light seal.

I guess that if the material wears it could develop tears and loose parts that could impede the second curtain.

Dave..

 

[wolves3012]

Fidget's explanation seems pretty good to me. There can be the lightest contact against the strips but very little or else they'll drag on the curtains.

 

[Grytpype]

Thanks, fidget and wolves3012. I'll try to set it up with zero clearance, or extremely light contact, and check there is no noticeable slowing of the 2nd curtain.

One more thing, a bit off original topic. I'm ready to separate the top-plate from the crate, but I don't want to do this, and take out the curtain-drum, until I am sure I can get the restrictor gears back in mesh correctly. I think I have probably taken enough pictures of curtain positions, cocked and uncocked, to be able to do this, but is there anything I should mark or check to make re-assembly easier? As far as I can see, the restrictor gear is a plain gear without a stop-pin or anything, so I haven't managed to work out yet how the curtain travel is limited.

Steve.

 

[Grytpype]

Have I got this right? The position of the 2nd curtain at the uncocked position is controlled by the coupling pin (engaged in the top of the 2nd curtain drum) reaching the end of its slot in the 1st curtain upper drum. So I should be able to get the gears meshed correctly if I note the position of the disc above the top-plate which carries the coupling pin.

Presumably the restrictor gear is what stops the 1st curtain at the uncocked position? I assume that how it does it will be obvious when I take it apart!

P.S. Correction to the last point: The large gear is 'slack' in cocked and uncocked positions, so it must be something else I haven't spotted that acts as a stop on the 1st curtain.

 

[Grytpype]

Finally took the top-plate off, and the curtains out. The 1st curtain stop I was looking for was, of course, under the gear wheel attached to the lower 1st curtain drum - a pin fitted to the bottom of the crate. I should have spotted its outer end earlier, but it was hidden under the 1st curtain latching disc, which I hadn't yet removed.

I like to try and figure out how things go together before I take them apart, and I think I have probably done that now, so with a bit of luck I should be able to get it back together again!

Steve.

 

[wolves3012]

I see you have it sussed now. The pin in the bottom is what controls the drum and the pin at the top controls how far the pulleys can move relative to the drum (I may have that bit back to front but I'm sure you follow by now!).

It does make good sense to try and figure things before you pull them apart! Be aware that putting it all back in the crate is a damn PITA. You have to get the tension rollers back in place whilst keeping the curtains in the right place etc. Be prepared for several attempts to get it right.

 

[Grytpype]

Thanks for the advice. Fortunately, I am used to PITA reassembly jobs!

The reason for the puzzlement was that I had been reading articles describing the shutters in a Zorki-1 and a FED-2 and it is clear that these are arranged differently to the 4k. The lower face of their shutter-drum gear is flat, so the curtain travel in them must presumably be restricted by the gear-wheel at the front, hence the gears have to be meshed in the correct position for the curtain positions to be right.

I thought that the 4k would be the same, but as I see now, the curtain travel in this camera is limited by the arcuate slot (about 300°) in the lower face of the shutter-drum gear and the fixed pin in the shutter-crate. This means that the larger gear at the front of the crate is simply an intermediate gear connecting the pinion at the bottom of the sprocket-spindle with the drum gear, and it should not matter how the gears are meshed.

Steve.

 

[Grytpype]

Setting the rear baffle so that it did not impede the curtains turned out to be much easier said than done! In spite of the large mounting holes in the plate there was little or no adjustment available since the width of the threaded plates that the fixing screws go into meant that the plate was held just about as far down as it would go. I filed quite a bit off the sides of the threaded plates to allow some movement, but this still was not enough. Also, moving the baffle forward meant that there were clearance problems between it and the curtain drum and the 1st curtain roller, and the side baffles were not going to fit properly.

The only solution seemed to be to find some thinner light-seal velvet, but then I realised that the velvet strips looked as though they were a good deal wider than the bottom of the hollow in the baffle-plate where they are presumably meant to fit, and that they were therefore standing much too high on the plate. I took them off (lighter fluid removes the glue), cut them down to about 2/3 of their original width, and glued them back. This looks much healthier, and the curtains run freely.

This camera was very clean, inside and out. I wonder if this is because it never worked properly and was abandoned early in its life!

 

[wolves3012]

Well if it's working now, well done. Go take some pictures with it and enjoy...