I have a 1977 300D with the 617.912 engine and the loop type glow plugs. I am replacing the original injector nozzles with rebuilt Bosch injector nozzles part no. NA 30 X for the non-turbo engine. The rebuilt nozzles have a part included called the nozzle plate (sealing washer) according to the MB engine manual 1991 Ed. My injector nozzles have never been changed and carefull inspection shows that my engine does not have nozzle plates.

Should I use the nozzle plates as the MB manual recommends?

The MB manual shows the nozzle plates with the pencil-element type glow plug and not the loop type glow plug my engine uses. Also, the MB manual states that the "resilient" type nozzle plates should be used from now on (pg. 07.1.4-230/2 F2).

If I am supposed to use the nozzle plates, then how are they inserted regarding the orientation of the nozzle plate's surface and which side contacts the injector nozzle (does the flat outer ring of the nozzle plate contact the injector nozzle or does the flat outer ring face down into the chamber)?

If I am supposed to use the nozzle plate, then why did MB decide it was needed now and not when my engine was made?

Thanks,
Tom