Zorki 4 shutter times issue

[lozz]

Hello,
Firstly, thank you to Wolves3012 for the excellent Zorki 4 CLA instructions - it's a great resource.

A little background. I acquired a Zorki 4 in very good condition both inside and out. The only issue seemed to be shutter times - the fast speeds seemed more or less okay but the slow speeds didn't function properly. Unfortunately I didn't note at the time if the second curtain was operating (more on this below).

When I came across Wolves3012's CLA instructions I decided to see if this would fix the issue. I followed the instructions precisely and there was remarkably little dirt or old grease - but certainly things moved more freely after.

My problems began when I tried to re-fit the slow-speed mechanism. I put it on and took it off so many times that I can do it in my sleep. Some times the ring gear would unwind completely, sometimes the ring-gear pin would not be in the right place etc. The main problem seemed to be that the second-curtain pawl was not triggering (I could do it manually) and therefore neither was the silver disk that sits under the bronze speed selector disc, although sometimes it would (note: I was very careful to check that the cam did not rest on the pawl and jam it). Eventually I realised that the pawl was a bit loose and moved laterally. I tightened the (loose) screws that held the pawl mechanism and this seemed to fix the problem - no movement laterally but free to move back and forth. This seemed to fix most of the issues for the high speeds, but the moment I selected one of the slow speeds the second-curtain refused to trigger. Initially I could solve this by selecting a high speed and it would go back to normal. Now it doesn't do that - I now have to manually trigger the pawl for the second curtain. The high-speeds are now intermittent, sometimes triggering sometimes not.

Some additional info: When not triggering, the first curtain wont go all the way across but stops at some point (depending on the speed selected). The winder is also loose until the last quarter turn (works normally after triggering second curtain). The clockwork for the slow speeds never seemed to work - I fear I may have damaged it by removing it so many times - although it did seem to function correctly out of the camera.

Apologies for the long post, but I wanted to provide as much information as possible. If anyone has any advice or fixes to stop me going mad I would be very grateful.

 

[wolves3012]

I've been having a think about this one, hence the late reply. In honesty, I'm not quite sure! Might be easier to explain how the mechanics are supposed to work and you can try and establish where reality differs and discover the fault.

Both curtains are released together by the shutter release. The first curtain travels freely until fully open. However, the second curtain is trapped by one of two mechanisms. For "fast" speeds and B, there's a curved arm that catches the travel until some point later in the first curtain's travel (which it never reaches for B), when it gets pushed aside. The latch is pressed inwards and downwards by a light spring and that could be the culprit here - too much or too little spring tension can be a problem, as can a sticky pivot for the arm. On "slow" speeds, the pawl you've noted traps the second curtain until the cam on the slow speed mechanism moves it, exactly as you've figured already.

With the slow speed mechanism removed, the second curtain is permanently blocked and never closes - unless you manually move the pawl.

I'd suggest taking out the slow speed mechanism and finding a way to block the release pawl in the released position (you could hold it aside with a fine screwdriver while experimenting or perhaps temporarily remove the pawl, with care, although it might be very fiddly to put back). Then try the speeds to satisfy yourself that all is well on ALL "fast" speeds. Note that 1/30 is a "fast" speed but 1/60 is a "slow" one - strange but true. Then you can unblock the slow speed pawl and re-fit the escapement and see how that goes.

If I can help any further, just ask! It's a bit difficult to diagnose a fault without the camera in front of me so I'm having a best-guess.


EDIT: just an afterthought, if the first curtain fails to open fully, there's either a lack of tension on the roller or there's too much tension on the second curtain latch spring (on the curved arm). Ether of those will cause the first curtain to stall partly open, because the second curtain latch can't release.

 

[lozz]

Wolves3012, thank you very much for taking the time to think about this problem and write me some suggestions. I am sorry for the late reply, but today is the first chance I have had to try your recommendations.

The first thing I now understand from your post is that the timing of the 'fast' speeds is totally independent of the Slow Speed Mechanism.' - well that sounds obvious 🙂 but I thought the cam was involved in the timing somehow. A question: so when a fast speed is selected should the pawl somehow be retracted so it doesn't interfere with he travel? If so, how is this done?

Okay, so with the Slow Speed Mechanism removed, and the pawl retracted with the aid of a tooth pick - all the fast speeds work properly, including 1/30 and B. To my untrained ear the speeds sound accurate, at least relatively, except for 1/30, which sounds a bit fast. But anyway they are working. In this situation all the curtain problems I mentioned in my first post disappear. So it seems that the problem is the related to the Slow Speed Mechanism itself, or how I am installing it.
I have a question about this part of your post Quote:

However, the second curtain is trapped by one of two mechanisms.

I understand the way the second mechanism (the pawl) works, but not the first. Firstly, is the "curved arm" and "spring" you mention, the one indicated by the yellow arrow in the image below? (sorry, I don't seem to be able to embed the picture, only a link)


https://www.dropbox.com/s/dezcyyc58z0l2rm/Zorki%20arm..jpg?dl=0

If this is the thing you are referring to, this is its action: (with the pawl retracted) as I wind the film advance to cock the shutter, the tab on the speed selector (the one that sits in the slots) moves counter-clockwise. As it gets to the 6 o'clock position (lens facing away from you) it comes in contact with the middle lobe of the curved arm and pushes it slightly outwards before stopping at about the 5 o'clock position. When I fire the shutter (in any of the fast speeds) the curved arm is pulled downwards and the the tab on the speed selector spins clockwise and stops at the 3 o'clock position. Does this sound correct?
After the CLA the curved arm moves freely up and down and back and forth, but I don't know if the spring tension is correct. The following picture is the curved arm at rest after the shutter has been fired - does it seem in the correct position?

https://www.dropbox.com/s/w90ziin8piw8dp4/P_20200425_151353.jpg?dl=0


If you have time, would you mind giving a brief run-down on how the curved arm catches the second curtain - I am really not sure how this works.

Now that I understand more, I will have another look and see if I can figure out what is going on.

Thank you once again for your help.

 

[wolves3012]

The part you arrowed in your picture is indeed the "fast speed" 2nd-curtain latch and the spring looks to be in the correct position as far as I can tell. Here's a more detailed description of how it works...


When the shutter is fired, the curved arm drops down and is pushed inwards just as both curtains are released. The speed-selector centre boss has a "pip" on the first curtain piece*, as does the second curtain. The pip on the second curtain latch comes up against the curved arm and becomes trapped, stopping the second curtain but not the first one. After a certain amount of rotation, the first curtain centre's pip knocks the latch aside, freeing the second curtain and completing the exposure. The number of degrees before the second curtain is released depends on which speed is set, giving a variable-width slit. On "B", the first curtain opens fully without the pip ever knocking the latch aside so the second curtain remains held - until you lift your finger off the shutter button and the curved arm rises up out of the way.
(*actually this varied a little by model and I can't remember on the Z4 if there's a pip or the selector arm itself does the job.)

If the latch spring presses the arm too hard inwards, the first curtain may not have enough power to knock the latch aside, stalling both curtains. Likewise an under-tensioned first curtain can cause the same thing. Usually the latch just works properly or it doesn't (on all speeds) but I have had a Zorki 5 where the fastest speeds (500 & 250 only) stalled and the slower ones didn't. That required the latch spring to be bent back a tiny bit to reduce the tension. I think the faster speeds were more affected because on the slower ones the mechanism has turned further and built up a bit more momentum - but that's just my theory!

However, if the fast speeds all work properly with the slow-speed pawl out of the way, I don't think that's your problem. I'd be looking more closely at the slow-speed mechanism, including the cam and the pawl. You can leave the flash-synchro out until after you've sorted this problem, you'll be able to see things better without it fitted. When re-fitting the slow-speed mechanism, just take care to follow the instructions about winding it far enough and keep it there. You can't really wind it too far unless you get silly - it'll just unwind back to the proper place when fitted.

P.S. the slow-speed pawl is kept out of the way on fast speeds because the mechanism is unwound and the cam underneath keeps the pawl retracted unless the mechanism is wound up - so it's a kind of automatic default.

 

[lozz]

Thank you once again for your time and expertise. I am sorry I took so long to reply - I had urgent work and forgot to leave a post. Unfortunately I am still busy so the camera will have to wait a little longer...
Thank you again.