LOOSE RING ON BACK OF CAM BELT DRIVE...???

That's the (molded) "fence" on the cam belt driven sprocket that has broken off -- the cam driven sprocket needs to be replaced. Happens when people don't know how to install the timing belt and force the timing belt over the fragile plastic fence (and break/crack it). Maybe more importantly, is your timing belt is GONE! (Can't really tell in the photo.)

There is a fence on both the intake cam driven sprocket and the exhaust cam driven sprocket on opposite sides -- they are what prevent the timing belt from moving sideways and slipping off the sprockets. You can see the fences on the cam driven sprockets in this SPC figure:

https://www.ferrariparts.co.uk/diagram/ferrari/308-gtb-1976-fibreglass/008-timing-system-controls

(And note how the 1-4 exhaust cam driven sprocket fence is at the rear of the sprocket where your "ring" is now.)

PS The "secret" to not breaking those fences is to leave the bracket holding the Tensioner bearing loose and not tighten it to the engine block. This gives additional timing belt slack so the timing belt doesn't have to be forced over the fences. Once the timing belt is in place then tighten the nuts holding the Tensioner bearing bracket.

 

Stop driving it. Replace the sprockets.

 

Nothing. The fences are more a safety measure IF the belt has a tendency to move sideways one way or the other. On your car, the 1-4 timing belt may not have a strong tendency to move sideways, or its tendency may be to move towards the fence on the intake cam driven sprocket (the belt wear marks on your exhaust cam driven sprocket do seem to indicate that the timing belt has a preference to run at the front of the exhaust sprocket (away from its fence). But the short answer is "yes", you risk the belt coming off -- and the belt behavior at idle/low RPM may be far different from its behavior at high RPM.

 

I have no idea how much those OE sprockets cost. SRI used to have a service to weld the rings and replate the sprokets. But you can diy it at home if you weld or take it to a welding shop. It would be cheap just an hour shop labor minimum and cost you maybe 50 bucks. So I would weld all the sprokets with faces just to get your money's worth. There are places by me who plate as well but I would not bother plating but it looks nicer.

 

I think that's more on the 348 (or maybe 355) system (that has metal fences and sprockets) -- stock 308 fences and sprockets are molded plastic (over a metal core).

 

I forgot about that! It has been a long time since my 308GTS

 

Somebody sells replacement sprockets with metal rings... I forgot who.

 

I think Dave Helms is the one selling this.

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Well, then it will be $1,000 each.

 

The plastic section of the originals also tend to crack as well. Best to replace with metal versions when possible. Image Unavailable, Please Login Image Unavailable, Please Login

 

The original cam sprockets were plastic and tended to fail. The replacement parts from Ferrari about 30 years ago were changed to metal. If you still have plastic sprockets I would change them quickly before you have a major engine rebuild to worry about.