Timing Chain Stretch Question

[Fyeganeh]

This is not really a Porsche or 986 question per se.

My question is what is the biggest cause for stretching timing chains that makes them need to be replaced. What causes the most stress on the chain to make it stretch? Specifically is the most stress at start up ignition? Think of when you are on a bicycle and how from a start the strain on the chain is likely most when you first push down on the pedal to get the wheels rolling....

The reason I ask is modern cars have start/stop systems that turn off the engine at a stop light to save fuel. But then a car will have probably 10x more starts for the same number of miles. Does that then lead to quicker failure of the timing chain?

All of this started when I got a diesel Mercedes SUV with the hope of getting it to last a long time. So the other day I started to research how long diesels are supposed to last - and saw lots of stories about how they last up to 500K miles. But then I researched the specific diesel engine in my car and I saw some reports about the timing chain in these new cars wearing out at 70,000 miles.

Some people posted that it could be due to the start/stop in new cars.

So I know there are a lot of great mechanically inclined minds on this board who know a ton more than me and I thought it might be of interest to everyone who has bought a new car because if true - it would apply to everyone who has these new start/stop cars.

What are people’s thoughts?