http://www.shopsmithacademy.com/SS_Arch ... _Belts.htm
Is the Shopsmith Academy Video. It's older when video resolution was not as high as we are accustomed to today.
Look at the eccentric and drive assembly. Pay attention to the washer and screw that hold it in place and make sure the washer that covers the eccentric is a fender washer and covers the bearing face lip to prevent it from coming out.
Make sure that the Serpentine Belt as you referred to it (Poly-V) as named by Shopsmith, tracks vertical, that is: the splines line up directly and are not offset or it will bind.
The belt viewed from the top should be relatively centered with a few splines on either side.
Tension it as described in the video.
You may benefit from a large format exploded parts list that I put together some years back that shows the relationship of parts to each other.
Go to
https://www.shopsmith.com/ss_forum/view ... 90#p185690 Scroll down the page and find the link to the Headstock Drawing 3.0.2
Mark V Headstock rev. 3.0.2 - Click that link, and within the post it links you to, download that PDF. It is reoriented to make the visibility of the assembly more understandable.
While you are there you will undoubtedly notice a link to My Google Drive where you will find the document on the main page titled Buying a Used Shopsmith V2.PDF. It will get you grounded on what you have and help make sense of the other forum entries here.
Equally, you will find a ton of other beneficial documents in the various folders under My Google Drive, (all free downloads)
In the Bearings folder you will find a Shopsmith Bearing Guide that has pictures of the various components (including where the belts go) and discusses the various changes through the years that might be present in yours, based on when it was made or perhaps upgraded through the years.
Once you understand it, the genius in the design that has endured 60 years, is the simplicity of how it works together to do what it does.
Everett