Repairs page 2

QUITE a few Zenit EMs and later mechanical modelshave shutter releases that are either heavu or jerky or both. They're nothing like as smooth as the releases on the earlier B and E models.The EM and later models have automatic aperture stop down whereas the B and E don't. Moreover, not all EMs and later models have heavy releases so it follows that it must be an adjustment for the auto stop down but not all Zenits are properly adjusted.
When I inverstigated the heavy release on some of my Zenits I found that in its fully forward position the plate that operates the stop-down pin on the lens fouloed the body inside the lens throat before the shutter fired. Further pressure to fire the shutter tried to move the plate still further forward but instead flexed one of the arms on which the plate pivots.
To investigate further, I took the top plate off an EM that had a very heavy release and the reason soon became obvious. There is provision for adjustment but it was way out. It isn't a difficult adjustment to make but you have to take ofrf the top plate and the pentaprism to get at the

Auto aperture adjustment on Zenit EM and later nmodels

adjustment screws. It might just be possible to do it without taking off the pentaprism, and I suspect sopmeone had tried that with this EM, but all they managed to do was mangle the slot in the bottom adjustmnent screw, the more difficult one to get at. It was still very tight when I loosened it. They obviously hadn't succeeded because the adjustment was still way out. In any case, taking the pentaprism off is no trouble, and it gives you a chance to clean the dust off the top of the screen and renew the foam pad over the pentaprism which will probably have gone sticky and horrible.
Before going on to making the adjustment I'll run through the operation of the auto stop down. When you get the top plate off you'll see that the release button pushes down a lever. This lever runs forward and is an extension of a rocking bar. Also attached to the rocking bar is a small roller. This rollewr engages with a triangular shaped cam plate which is held to one of the arms of the aperture plate by two screws. The cam plate has slotted holes to allow it to be adjusted.
Before you presss the release lever the roller is below the apex of the cam, either just touching the lower sloping face or very close to it. When you press the release lever down you'll see that the roller rides up the lower face of the cam,

This should be the position after taking the first pressure on the shutter release

pushing it back so that the aperture plate inside the lens throat moves forwards. If the adjustment is correct, then with the aperture plate fully foward, almost but not quite touching the insde of the body, the roller should be sitting right on the apex of the triangular cam plate.As you press further on the release lever to fire the shutter the roller runs along the upper face of the cam plate without moving the cam back any further. If the aperture plate moves forward to touch the body before the roller reaches the apex of the cam, things come to a stop. You have to press quite hard to move the roller up to the cam apex. This tries to move the plate further forward, but as it can't move, one of the arms carrying the plate has to flex, and you get a hard, jerky release instead of a progressive and smooth one.
OK, now you know what ought to happen, I'll go through the method I used toadjust things and avoid a hard spot in the release travel. I hadn't got a manual of any sort, so I worked by trial and error to find the metod I found

When you press the release further to fire the shutter the roller runs along the top sloping face of the cam without moving it.

easiest. I moved the aperture plate forward to see where it was fouling, and put a piece of card about 1/32 inch (0.80mm) thick between the plate arm and the part of the body where it was fouling. Then I pushed down the release lever and watched the roller as it moved up the lower face of the cam. loosened the two screws holding the cam and adjusted it so the roller was just on the apex of the cam. It stopped on 'first pressure' below the apex of the cam, so I loosened the two cam screws andadjusted it so that the roller was sirtting right on the apex.before tightening the screws again. It took a bit of fiddling to get it right, but it wasn't difficult. Then I took the piece of card out and tried the release again. This time when I took the 'first pressure' the roller stopped on the apex of the cam. With further, quite smooth pressure, the roller rode along the top face of the cam without the cam moving any further backwards.
There was a further adjustment I wanted to make. The release lever was quite a long way from the plunger which releases the shutter. This didn't affect the smoothness of the release at all, but it meant there was a lot of free play and travel of the button before taking the first pressure, and I didn't care for the feel of it. The only way I could see to reduce this gap was by bending the lever down slightly. I did this by trial and error till I was happy with the feel of the release. This was when I had just a small gap, about 0.015 inches (about 0.38mm) between the lever and the plunger after taking the first pressure.
That deals with the last part of a CLA, the adjust part, and cleaning is straightforward enough with a small brush dipped in Ronsonol or similar lighter fluid, so on tothe L or lubrication, which gets the release even smoother. Wher I used oil I used just the smallest amount. It needs tobe only on parts where they touch, not all over the surrounding area. Many people err on what they think is the 'safe side' and use far too much. All they're doing is making a magbet for dust which turns the oil into a grinding paste.

This is where the arm of the aperture plate was fouling the body

     I use an upturned pocket watch glass, actually a plastic UB or Unbreakable, as watch repairers call it. Into this I put just one drop of oil carrued over on the end of my largest instrument screwdriver. Then I take the smallest of my screwdrivers, dip it inthe oil and touch it against the part I want to lubricate. It carries quite enough oil to do the job. I used to use clock oil ti my local watch and clock repairer closed. Now I use a silicone oil from Tandy which I find does the job very well and doesn'r migrate badly. It says on the bottle that it's guaranteed not to thicken or dry out within 10 years. which is good enough for me. For grease where ne3eded I use a white high melting piont grase from my local auto shop, actually Castrol PH, but I'm sure there are similar other brands.
     I lubricated the parts as follows: oil on the spindle of the roller, on the release plunger and on the rod where part of the shutter relaese linkage goes down through a hole in the body. I also put a tiny amount of oil on the pivots of the aperure plate evn though it swung freely. I put a smear of grease on the face of the cam where the roller runs even though it rolls and doesn't slide. Also, the sleeve round the release plunger has a forked extension which runs up and down one of the pillars on the body. It stops the sleve turning when you set it to rewind. It was a vfery loose fit, but on the basis that where parts rub there's friction I greased it lightly. On the underside of the release lever you'll probabhly find marks where the shutter release button slides alaong it. I put a smear of grease he, and also lightly oiled the button where it passes through the top plate.
     I hope this has been helpful to you in finding and curing the cause of a heavy or jereky release on your auto-aperture Zenit.