[marktwain54321]

It's interesting BMW approves the use of "plastic" parts in their engines. They pay engineers to calculate the MTBF on every part. In this case, a 3rd party company that manufactured the chain tensioner is possible the blame for a weak chain tensioner. Weak chain tensioner allowed chain to oscillate causing vibrations in the chain, which resulted in the likelyhood slip on the gear teeth, faster wear, and additionally caused micro cracks in the plastic guide leading to total failure of timing chain assembly and worse destroyed engine.
There are owners of older BMWs with the M54 engine with over 180K miles and they have no timing chain issues.

Placing plastics parts in their engines, is like planning for failure? I would call that = "Extreme capitalism!" A longer lasting vehicle would mean less continued maintenance, and fewer sales on new vehicles. One of BMW sales tactics is to steer the consumer from the high cost of repair/s into a new vehicle.

Perhaps BMW documentation will show they approved a design change request in the chain tensioner from the 3rd party company. Perhaps different spring material was suggested, perhaps mass/size of spring coils, perhaps they didn't account for heat weakening the new spring degrading it's performance causing malfunction to the chain tensioner, directly affecting the timing chains function which can lead to total loss of engine.

There are many models affected by this issues, a recall would place a big dent in BMW profits.