I just finished cleaning and testing the injectors on my father's 81 300TD and was about to reinstall them, when I had a little surprise: one of the prechambers had a much bigger hole (where the injectors goes), than the others. I assumed at first that the previous owner had stacked two heat shields on some of the prechambers, but I couldn't get these "supposed" second heat shields out. I also noticed a difference in depth between the two holes (you can see it in the pictures).
So, are these heat shields or just a different type of prechamber?

EDIT: Deleted redundant pictures.
Just to clarify: cylinder 1 has the small hole, and cylinder 2 the larger.

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