Quote:
Originally Posted by airbus
Timing chain stretch: How do I check this? Are there any other signs that would point there?
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See post #5 in this thread:
http://mbca.cartama.net/showthread.php?t=24112
What are the signs that the engine/car was abused?
Timing chain stretch will give you an idea of how often the oil was changed. Using non-synthetic diesel-rated oil and changing at normal intervals of 5k miles, you should find 2 degrees or less of stretch assuming the engine has 160k miles.
An engine stethoscope would be really usefull to narrow down the location of the noise. There are more than a few external things (like air cleaner bracket broken, or totally collapsed engine mounts) that can make a lot of noise. On the OM60x engines, fossilized o-rings on the oil filter stem can cause the engine to make strange and alarming noises.
If you pull the injectors to look at the pre-chambers and check the condition of the pins, the seal rings are a one-time use item so stock up with new ones before you go that route.
If the noise is injector related, it may remain after the injector(s) is fixed because the carbon deposits in the pre-chambers are still there and will affect combustion noises until they are burned out.