Yes, I know the rule is never to lubricate shutter blades, and I haven’t. I acquired an old Zeiss Ikonta which had that common ailment, sticky slow shutter speeds on a Prontor-SV shutter. So I tipped in a small amount of lighter fuel, which normally does the trick, exercising the shutter a few dozen times, and it seemed to free up, with 1s sounding like 1 second, and so on. It seemed perfect. But after an hour or so, the shutter just stuck completely, and a few more drops of lighter fuel freed it up. Then the cycle repeats. I’m wondering if the lighter fuel is reaching the blades and acting as a lubricant, and when it dries out, the blades are causing the shutter to stick, rather than any gunge in the shutter assembly itself. I’m not sure.

I know there’s a tip elsewhere on this forum that if it’s absolutely necessary, shutter blades can be gently lubricated by a finger smeared lightly in fine graphite pencil, but I’m hesitant about this in case I’m on the wrong lines entirely.

I’d be grateful for any pointers. This little Ikonta 521 is otherwise a perfect little peach and I’m getting restless now about putting a roll of film through it.

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What you’re experiencing is very common. Most of us have come across it an one time or another. What has happened is that the original sticky slow speeds were caused by dirt/dried oil in the slow speed escapement train. When you used the lighter fuel you freed this, but the old oil on it has washed down and distributed itself on the shutter blades. When you add more lighter fuel you dilute this oil enough to break down its surface tension but it reforms as soon as the lighter fuel dries out. It’s got to be washed out completely – adding graphite or anything else will only form a sticky paste.

You don’t say how far you disassembled the shutter, but it’s best if you take it off the camera (usually a screwed ring round the shutter housing inside the camera), remove both the front and rear lens elements and take off the speed control plate so that you can see all the mechanism.

Then there are two ways of getting it clean, the long way, which purists will tell you is the ‘proper’ way, and the short way which, for me, works about 90% of the time. Try the short way first.

Lay the shutter in a shallow plastic tray, something like a ‘chinese take-away’ box, keep flooding it with lighter fuel and working it while it’s wet to try to wash all the old oil out. Keep doing this until the shutter works when it’s dried out.

Lighter fuel in small cans is quite expensive but it’s only refined naptha. If you can buy ‘commercial grade’ naptha it’s cheap enough to cover the shutter with it and swirl thigs around. On really sticky shutters, as an alternative to naptha or lighter fuel, I have used an aerosol of carburettor/injector cleaner from my local auto store. It’s a very powerful degreaser, two floodings are usually enough to get the shutter really clean, but be careful how you use it. ALWAYS use it in the open or in a ventilated outhouse because the fumes are nasty things to breathe. Second, don’t use it if there are any plastic bits attached to the shutter because some of these injector cleaners will dissolve many plastics.

With regard to operating the shutter while it’s still wet with cleaner, the shutter should work in ‘B’ mode with the speed plate off, or you can put the plate back on and just hold it in position while you work the other speeds. A tip for replacing the speed plate – put it on in approximately the correct position then give it a gentle turn anticlockwise till you hear a click as the pins drop into their respective slots.

If this is the first time you’ve been inside a leaf shutter have a look at Daniel Mitchel’s site
http://daniel.mitchell.name/cameras/index.html
and scroll down the index on the left till you come to ‘shutters’ and have a look at ‘Prontor SVS’, which is an updated version of your Prontor SV.

Daniel gives a detailed, illustrated, blow-by-blow account of stripping a Prontor completely to pieces for cleaning (the ‘long way’).