Try a bentley manual. I guess it could not have the "240d" specifically. A parts sight may have an exploded diagram.
The best place to find a diagram of timing chain and gear alignment would be at a Mercedes dealer. Dealers keep many manuals and periodicals listing all the thousands of parts of their vehicles.
You would find that info in a shop repair manual for that vehicle.
That would be a timing chain for this car.
It Would Have A Chain. Best To You
That would have a timing chain.
4.0L I6-NO 4.7L V8-NO 3.1L Diesel-NO 2.7L Diesel-NO It would have a chain.
Timing chain. If it had a belt you would see the replacement interval in your manual.
It has a chain and gears. NO BELT. There would be no reason to fool with the timing chain and gears on that year engine. The chain and gears would out last the engine.
Timing belt or chain may be bad.
it has both chain and gears
Generally a timing chain is good for the life of the engine, so myth.Generally a timing chain is good for the life of the engine, so myth.
Your timing chain may be worn to the point it is jumping a tooth and thus changing the timing. If you can hear the chain that is a good sign it is worn. I would inspect the timing chain.