Mercedes hasn't ever issued a mileage or time schedule to replace the timing chain!!!
The only engine that has ever had a scheduled inspection mileage is the 190E 2.3.
It is suggested that the timing chain be inspected for excessive stretch whenever the valve cover has been removed.
The more frequent oil changes the less chance of failure of the chain & other related items.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS M.B. TECH