All six injectors were new injectors, with new "gtd" nozzles fitted, set to 170bar, I purchased them from Anders. They looked& worked great for several months.
At the time of installation, I did not notice nozzle/nozzles being off centered.

I'll take the bad injector apart to see if I can spot visible damage or dirt, but I doubt it failed due to foreign material. I would say that the nozzle got misaligned by the turning force when the injector itself had been torqued into the head, maybe the crush washer/injector shield did not sit flush enough or idk. But it ran so well for long, only then it failed.

Whatever it is, im glad that those bad sounds were not caused by an internal major issue.

Unfortunately a diesel inj tester isnt part of my tool hoard yet.

Injectors with "GTD" nozzles set to 170
 

Same thing happened again, today,

On the way back home from a circa 100mile road trip. Regular driving, no issues no hard driving nothing extraordinary...then:
Suddenly I heard knocks and saw excessive smoke, luckily I was on my exit near home, only a mile away and made it home gently.

Soon after I got proper d24 tools together and loosened injector tops one by one and turns out this time it was cyl #4 injector acting very stupid.
I wanted the bad one out and have thecar running well again. This meant adding one of the "old" injectors in.

Hard lines got loosened, securing brackets got removed, 2hard lines turned away and #4 return lines removed then injector taken out.
New bosch seal/washer, old worn injectors out of trunk reopened (sealed in 987 layers of serurity foil, capped etc), i picked one injector, added copper antisieze and torqued it to 52 and reinstalled everything including new return lines. Bled the injectors all gently tightened all nuts and installed the important securing clamps in the hard fuel lines. Sprayed it all down so i could see leaks and errors. No issues.
***Watch water hoses when you use chemicals!

Hard knocking is gone, no injector sounds, smoke stopped.
Starts and runs fine, no leaks, no air in system. And runs good.

Facts:

2 of the 6 new injectors are "out" and went bad. In such a small time. Maybe only a few thousand miles apart . ... I'm left thinking what is going on?
And why.
Inspecting both of them i can see that the tip of the injector nozzles are off- centered. The gap at the perimeter is large on one side and nonexistent at the other side right across ...diagonally across ....on the same nozzle.

I just want a reliable set of injectors now, probably the stock ones but "new" , well set to fact spec 155.

Unless someone can explain this and suggest another plan.
Thanks. Picts i took are too big in size for this forum.

I will try reassembling those two failed injectors one day. Maybe

Are you looking for additional information different than what we have discussed above? Nozzle needs to be centered in the injector body, can be done even without the Bosch tool. Crack the injector open just enough to be able to move the nozzle around until it's centered, then torque it back together.

Where were these injectors from?

OK I see you got them from forum member Anders. Why don't you contact him and explain the situation to him?

Have you taken the two failed injectors apart to see if you can find a reason for the problems? Does the needle move freely in the nozzle? Any broken springs?

What kind of fuel do you normally use? And do you put in any kind of lubricity additive (biodiesel, Stanadyne, PowerService, etc)?

I have seen injectors fail with these symptoms when the needle hangs either due to lubrication failure and resultant scuffing, or contamination from a failing injection pump or elsewhere that jams the needle open. In that case you may be able to clean it and get it working well again, but you will want to know what was the source of the contamination.

I would like to know how these injectors did fail. Are you running a 12mm pump? I have came to the conclusion that pop set at 170 bar and the 12mm pump is a bad combo. The injectors tend to break springs, this will cause pre-injection and the knock. I have also seen the stock Bosch injectors set at 155 break the spring too.

If you want to send the injectors to me I will drop the pop pressure back down to 155 bar, and I will look into what happened on the two that failed.it will be free of charge just pay to ship them to me.