It seems you have some mixed up info on BMW cars, and potential issues. I have owned BMW cars of 3 different generations.
1981 518 (E12) M10 engine, inline 4, sohc, duplex chain. No issues for 300 000km
1986 320i (E30) M20 engine, inline 6, sohc, timing belt, manual tensioner. Replaced every 60...