This question has always puzzled me, as spacing (or overlapping frames) has not been a problem with any of my Pentacon Six cameras; however, it appears to be a big problem for some people or for some cameras.

There are three things to try if you get uneven spacing with your Pentacon Six or Exakta 66:

• First, and most important: load the camera following my loading instructions, which you will find here.  (These are based on Ron Spillman’s loading instructions, to which you will find a link on my loading page.)

In most cases, that should totally solve your spacing probems forever.
An important detail of the loading process is keeping the film tight: you need to hold the supply spool with a finger or thumb, and as you advance the film to the start mark you should be able to see the tooth marks of the film spacing roller at the top and bottom of the of the backing paper.
 
• Second, if you have done this carefully and still have uneven spacing, try Rolf-Dieter Baier’s film advance instructions, which are available here.

Just in case there is ever a problem with that web link, essentially, Mr Baier’s procedure involves the following:
After firing the shutter in the normal way, before winding on, press the shutter release fully down (it won’t fire again), and hold it down while activating the advance lever only until the lever is in a straight line with the front of the body.  (If you feel some additional resistance when advancing the film, slightly reduce the pressure on the shutter release button.)  Then take your finger off the shutter release and continue moving the advance lever to the end of its travel.
Guide it back to its rest position with your thumb, as always (never let it swing back on its own).
I have never tried this procedure, as I have never had a spacing problem with any of my cameras, but I am told that it can help in some cases.

• Third, if you still have uneven spacing, your camera is faulty and needs to be repaired.

Hand it over to a specialist repairer who knows these cameras.  You will find details of repairers here.
OR send it to Rolf-Dieter Baier in Germany for repair, and installation of his Film Advance Control, which gives a visual indication when the film has advanced far enough.
I have also not had this advance control installed on any of my cameras, as I have not needed it, however, I have bought other items from Mr Baier and find him extremely knowledgeable on the Pentacon Six and Exakta 66, and extremely reliable.  I recommend him.

1.  Load the film in the normal way (as shown on this website!), close the back and wind and fire to the first frame.
      You may find it helpful to have the camera on a tripod for the rest of the process.
2.  Remove the lens.
3.  Set the shutter on “B”.
4.  With one hand fire the shutter and do not let go of the shutter release.
     This will keep the shutter open, and you will be able to look at the film in the gate.
5.  With a pencil or felt tip draw round the inner edges of the film gate, and write a “1” in the middle of the frame.
6.  Remove the pencil and let go of the shutter release.  The shutter will close.
7.  Advance the film in the normal way.
8.  Repeat steps 4 and 5, above, this time writing “2” in the middle of the frame.
9.  Continue in this way through to the end of the film.  You can even mark the 13th frame if you think you might get 13 shots on the film
     – although if the film has been advancing correctly, you’re likely to see the end of the film in the middle of the gate.
10. Wind off the film in the normal way, open the camera, and spread out the film.