How are the cams driven on the OM642? Timing chain? Timing belt? Timing gears?

Chain

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Jim

A timing chain drives the intake camshafts on both heads. The intake camshaft in turn drives the exhaust via gear drive. You can see this arrangement by removing the oil filler cap. Be sure to reinstall it correctly, it's easy to get it on at an angle, and the resulting oil dribble down the block will collect on the alternator and kill it.

What is the expected life of the timing chain? Should it be replaced at some certain mileage? The car now has 217,000 miles and the chain is the original. Currently driving the car 2,000 to 3,000 miles per month.