A lot of confusing and conflicting information here. Here’s my two cents.
Let me start by strongly reiterating Rico and casdave’s advice not to adjust any of the screws on the head block. First, it will absolutely, positively not fix the problem you are reporting, and second, it will absolutely, positively screw up the machine’s recording and playback capabilities beyond your ability to restore them. Head settings are NOT a user-adjustable control, and require test tapes and equipment and a knowledgeable technician to adjust correctly. The tapes and the technicians are as rare as hen’s teeth these days. Don’t touch those screws!
I believe that some of the terminology used by previous posters is incorrect, or at least at odds with my experience. Here’s my understanding of several key terms:
[li]Full-track = 1 audio channel across the full width of the tape. Uni-directional recording (i.e., no flipping the reel and playing the other side).[/li]
[li]Half-track = 2 audio channels, each taking about half the width of the tape. Can be bi-directional mono, in which case you can use the other side, or half-track stereo, in which case you can’t. [/li]
[li]Quarter-track = 4 audio channels, each about one quarter of the width of the tape. This can be bi-directional stereo or uni-directional 4-track. (The latter was used mostly for semi-pro and home recording studios.)[/ul][/li]
Antonius Block and Rico assert that on quarter-track recordings the stereo pairs are on the same half of the tape width. This is incorrect. If it were true, then playing back a four-track recording on a two-track machine would not result in the mixture of forward and backward sound that MsRobyn is reporting. Instead, you’d have a mono playback of the two stereo tracks, which, although perhaps not ideal, would be preferable to what you are getting now.
No, in quarter-track recordings left and right of side one are the first and third tracks from the top edge of the tape, and R&L of side two are the second and fourth tracks, respectively. Like so:
Side 1 left
Side 2 right
Side 1 right
Side 2 left
(Ideally, I would have printed the 2nd and 4th tracks upside down.)
The OP states that the tapes in question are four-track (i.e. quarter-track), which leads me to conclude that your playback machine is half-track. If this is the case, there is simply no way to get clean playback of any bi-directionally recorded tapes from this machine. (Of course, anywhere that side two is blank, you will get relatively clean sound.)
But for any quarter-track tapes with content on both sides, this machine will probably not work. You’ll have to find a quarter-track recorder, or use a service like that linked by flex727.
However, some half-track recorders did have quarter-track playback heads. It may be that by changing some jumpers or using different output connections, you could access those heads and get good playback. If you can tell us the brand and model of the machine, we may be able to find out.
BTW, the up-side of using a service is that if these tapes are very old, or not in very good condition (a fair assumption for almost any R-T-R tape) the service will know lots of tricks to preserve them and get the best possible recordings off them. Tapes that are very old, badly stored, cheap quality, or any combination of these three, will often shed the magnetic oxide material as they are played. This clogs up the heads, requiring frequent stops for head cleaning (a PITA), and also degrades the recording further. Some tapes are so bad that may only have one good pass in them. A good service will know how to deal with this. (Hint: it may involve baking them! Really!)
I hope this helps.