Ok, several things!

One, 15 ATDC is correct if you used the pump locking tool, as that is the point at which it locks the pump. This is NOT the same as start of injection timing, that is still 24 BTDC if you measure with a drip tube.

Your knock is most likely leaking pressure valve holders seals (no smoke, but rought running and knock below 1500 rpm right?)

Retorque pressure valve holders -- loosen after removing lock rings and injection lines (you need a splined socket), then tighten to 30 Nm, loosen, tighten to 30 Nm, loosen, then tighten to 35 Nm. If you don't follow this sequence you can damage the pump from over tightening, or the seals will leak. Quite common on the 603 for some reason.

Timing this engine can be set dynamically with the proper tool.

I would check the pressure valve seals -- crack the injector lines at the injectors one at a time and see if the knock dissapears on one or more cylinders. If it does, retorque the appropriate pressure valve holder.

On my 603, one of them was loose enough to unscrew by hand when I got the car....

I think the tensioner is a simple oil pressure type, not a ratcheting one on the 603.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!