injector heat shields for a 300D - are they necessary?

Robert

These are in fact called “injector seal rings” and they are VERY necessary! As Billybob states the correct part for the 617.912 is “Seal ring, MB # 601 017 00 60”.

NB! There are two types for these engines. The correct seal ring for the 617.912 fitted with the Bosch SD240/ anti-knock nozzles is 19.95mm outside dia. and has a 10mm dia. hole. On some older models with the SD220 nozzle the outside diameter is 20.25mm and the bore 6mm. These will jam if fitted to the 617.912 and you may even have to remove the pre-comb. chamber to extract them. The correct seal will always be easy to remove.

They are designed to collapse on tightening, sealing the nozzle face and injector body simultaneously. They can only be used once and must be replaced every time you remove the injector. To check before assembly lay the seal flat side (with counter-bore and lip) on the injector nozzle – there must be a gap of 0.4mm between the seal and the injector body.

Using the old seals will may require overtightening and will not seal on the nozzle face
Max torque for the injectors is 58ft-lbs - never exceed this as it is possible to strip the chamber retaining collar threads out of the head. 3 course threads in brittle cast iron!
This could spoil your whole day as you will need a new cyl. head!

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Beagle