The OM617 has no valve lifters.

One would have thought that the Mechanic would have checked the Camshaft and the rocker arms. No one has ever reported a broken valve spring but you can look for that.

Since 2007 when I joined I think one person had the valve adjusting nuts come loose.

As others said if when you do the injector cut out test there is no change in the sound then it is not likely rod or bearing. Because with no injection and the resulting pressure of combustion it would make it hard to make a knocking noise.

Of course a valve could be hitting a piston and that would continue to knock.

Specifically locating where the sound is coming from is a great idea and especially around the Vacuum Pump. Except for testing you should not be driving the Car till you find out what is causing the noise.

Note inspect the Air Filter Bracket to see if it is broken or the rubber attachments are not stripped out or broken. When mine was loose I thought that the engine was going to come apart.

Check the torque on the bolts holding down the rocker arm assemblies.

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84 300D, 82 Volvo 244Gl Diesel