Ladas had chains made from linked spaghetti hoops,
Lada's didn't have any of that chains or belts nonsense at all.. they had push-rods!
Chains will always stretch, as the pins will wear, even if the chain is permanently immersed in clean oil.. (albeit then very slowly). Stretch can be compensated for by a relatively simple sprung sprocket tensioner though.. so it's hardly a big deal.
If the chain wears or the tensioner stops doing it's thing, you risk the chain lifting off the sprocket (camshaft end being the most vulnerable) and when it does that, it will either leap off the sprocket and jam the whole cam drive (even Twin Spark owners can only imagine what that will look like!
) or it will rub against the inside of its cover.. making a rattle. If it's internal to the engine (to immerse it and the tensioner in oil) then it will dump that metal swarf into your oil... So, chain lubrication and tensioning is rather crucial.
I can only imagine that a cam-chain is more expensive to make and more expensive to assemble than a belt, to explain the rise of the belt.
The best solution (apart from push-rods!
) has to be gear driven cams.. no maintenance, no adjustment, no tensioner. Dunno what's wrong with them, that nobody is using them..