I recently bought a Sputnik that was in beautiful shape although it did have a small adjustment problem in the shutter. Since I have just finished opening it up to get at the shutter, I thought I might share what I learned. First of all, the Sputnik is a very simple camera and I can't think of anyone whom I would warn against working on it. 8-)
There are three lenses in a row on the front of the Sputnik and they are all geared together so obviously the center one turns anticlockwise when the outer ones turn clockwise. The center lens is the finder lens and it focuses the finder image on the ground glass. It has a reverse thread. For adjustment, it has a band with distances marked on it and two tiny set screws which can be loosened to allow that band to rotate free of the lens.
This lens' gear is attached to the lens directly and although I don't immediately see a way to loosen that connection, it is not required to do so.
The left and right picture-taking lenses have gears which mesh with the finder lens' gear. These gears are clamped to the left and right lenses by tiny set screws much as the finder lens' distance band is clamped to the finder lens. However, if you loosen a taking lens gear's set screws far enough, you can remove the gears right off the front of the lenses. These three set screws per gear are found equally spaced around the periphery of the gear boss and have axes which are perpendicular to the axis of the lens.
The shutter timing mechanism is in the right taking lens assembly. The left lens' shutter is operated by a lever connecting it to the right lens' shutter. After removing the gear from the right lens, you will see a D-shaped cam which takes a two-pin spanner or a pair of fine-tipped needle-nose pliers to rotate it. The idea is to rotate the cam until its rounded section is out of the rounded cut in the shutter assembly. Having done that, you can now rotate the plate on which the D-cam is mounted until its locking tabs line up with the rounded cuts in the shutter assembly.
When the locking tabs are lined up, you can remove that plate and then the shutter timing mechanism will be exposed. The top plate-cam you will see now is the shutter speed selector. It just lifts off. If you turn it to B it can be replaced easily. An interesting thing I learned is that there is an unmarked cam position between 1/60 and 1/125 second. I wonder if it is 1/90. I will measure its speed when I get a chance.
As you may have been able to infer from the discussion, this camera uses front-cell focusing. As long as the opportunity presented itself, I cleaned off the forty-year-old grease and re-lubed with a non-migrating silicone grease.