Both of my Benz's have around 170k miles and they both run great. I have been hearing that the timing chain should be changed at 100k. Should I change them even though I am having no problems.

Are there any preliminary signs that I should know about so I will know that the change is going bad?

How long do these gas engines last? 300k? 400? WHat happends after that, just rebuilding????

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'89 420 SEL
'90 300 SEL
'84 300 SD (sold it)