zit501

Hi Guys,

I appreciate you reading the little story below, and perhaps offering advice.

First post here, mainly since it's no me who owns the Merc, rather my dad. It's a CLS350 with the M272.

A short story:
About 24 months ago he got the dreaded check engine light, which was diagnosed as the notorious balance shaft sprocket failure. The car was at that stage under 90k km, but due to its age it was out of motor plan.
His independent garage has an ex-Mercedes mechanic working there, who appears to know his stuff. Mercedes South Africa did not entertain any of my dad's arguments about how this is a well documented problem and so on, and in the end he just had to pay the whole deal. Through his independent garage though the bill wasn't too bad.

Fast-forward to about 4 months ago, so that's 20 months or so after the balance shaft repair (and about 30k km later). He starts getting an erratic check engine light again. I scanned the car for codes and there was a again a code for camshaft timing, much like months earlier. Only this time with my internet searching they seemed to rather point towards the also common magnet sensor failures that people report. Sorry, I can't remember what the code was, I just remember it being more likely the sensor than the balance shaft.
Then, about a month back my dad started hearing a brief rattling sound coming from the engine, I'm not sure if it was on startup, but I think so.
He finally got round to taking it into the garage about two weeks back, where they diagnosed the problem with the erratic check engine light as being a stretched timing chain...? They "claim" that this is also a common fault (even though I haven't read about any on forums, and lets not forget that the balance shaft and all related parts were replaced 20 months prior). Even more interesting is that they got the Mercedes service consultants out to do a warranty claim on this stretched chain. Mercedes replaced the chain and they reinstalled it. So until this point, no expense to my father... I was smelling a rat, but my dad said that he believed them. The workshop staff were all saying that "these chains are too weak, and that they stretch", "poor design", etc. I haven't found 1 post about chains being too weak and stretching, but maybe I just haven't searched hard enough.

THEN, they were due to deliver the car back on Wednesday, when they called him and said that they found the cause of the rattle noise, which they say are worn intake cam gears. And that they need to be replaced at a very exorbitant cost.. Now again, I may not be seeing the forum topics about people replacing their cam gears due to all the posts about balance shafts, but I would have thought I could have found at least one?
The car is now only on 120k km.

I would have thought that the rattle my dad was hearing was maybe the supposedly stretched chain. Even this stretched chain story sounds very fishy to me. But now replace the sprockets?

So, my questions are:
1) Do these cars show wear on the camshaft gears, specifically the intake ones which have the chain sprocket and VVT?
2) Do these chains ever stretech? Even after balance shaft replacement, and after only 30k km?
3) What do you think about all this?

Thank you for reading this long post.
Mark