I am looking in the CD Manual and all it has is "remove nozzle plates" in the dissemble section and in the installation section "only use resilient nozzle plates from now on." Indicating the newer heat shields.

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84 300D, 82 Volvo 244Gl Diesel

After thinking awhile,I believe those seals were updated to later version,earlier
version dropped. Must remove top hat seal.
Larger seal designed to keep heat transfer away from injector pintal, Mercedes
thought it was necessary.

These seals don't appear to be the Top Hat type. To me, they appear to be the more permanently fixed "S&K" type that gmog's post refers to. I suppose we could try damaging the shield to pull it out but I worry that is not what is meant to happen.

Anyone on here face this issue in the past? Did you screw in the new injectors and call it a day?

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Well gents and ladies, I've changed my opinion about these odd-ball heat shields - they are removable. Thank you Screwdriva for creating this thread and asking the question. It forced me to take a closer look at one of the pre-chambers I have in my stash, and to ask fresh questions myself.

1 - Is the heat shield riveted in from below? Take a look at this:



The above photo is looking into the pre-chamber through the hole the glow plug tip passes through. You can clearly see the bottom of the heat shield protruding through the hole. Also, it does not appear to be peened over, or riveted in.

2 - If it's not riveted in, how easily removed is it? I used an appropriately sized drill bit inserted through the glow plug hole to push the heat shield out. I levered the drill bit against the edge of the glow plug hole and with a couple pushes the heat shield came out relatively easily. Here's what I ended up with:



And the heat shield itself (the metal is much softer than that used in the pre-chamber):








3 - Can the "normal" heat shields be used in these pre-chambers? I am less sure of this but I suspect the answer is "yes", provided the angle at the bottom of the chamber, where the heat shield seals against the pre-chamber, is the same. FWIW a "normal" heat shield drops right into place. I took a photo of that too but I am limited to 5 images per post so I'll leave it out.

So, is this heat shield the so-called "top hat" style? Sure looks like it could be. I'm going to dig out the books and see if I can find any information about this question.

Another question is how to remove these heat shields from above without having the pre-chambers out of the head. I think hercules' approach might be the thing to try (easy-out). If you can get a tool in there that grips and turns the heat shield I bet it will come out relatively easily. My previous attempts were hooking, pulling and prying and I had no luck.


Side note:

Something interesting I noticed while looking at this pre-chamber is that the top and bottom parts of it are threaded together. You can see this in the first photo I posted in relation to question #1. The lower part of the pre-chamber (top in the image) is made from a brighter alloy, and the upper part of the pre-chamber (bottom in image) is made from a darker alloy. Look at the exposed cross section shown in the edge of the glow plug hole and you can see the threads. Other types in my collection of pre-chambers are the same.

Attached Thumbnails

         

Excellent photographs!

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84 300D, 82 Volvo 244Gl Diesel

I dug in my book, "Service Manual - Engines 615, 616, 617.91", published in 1980, and also found reference to the "heat shield" as a "nozzle plate". In section 05-117, "Removal and Installation of precombustion chambers", there is a photograph looking down into the chamber and there's one of these old style heat shields visible. There is also a cut-away diagram that shows this older style.

Apparently by 1980 they were still using the older style. The text in 05-117 for sure references replacing these "nozzle plates" when installing the injectors, but makes no mention of the newer "resilient" style. I wonder when the design changed, exactly.

Thanks! Commercial photography is one of my gigs, and I happen to have some decent tools on hand. For these shots I used a Nikon D800E with a 55mm/f2.8 macro lens. Light source was an old "fresnel" light made by the Photogenic Machine Co. in the '30s or '40s.

Fascinating! Agree that the pictures are great.

Based on your inputs, it would appear that Mercedes did recommend switching out these nozzle plates. In that case, would replacements be available? Or would I have to swap out the entire pre-chamber to the newer type.

I'm tempted to bolt the rebuilt injectors into the existing pre-chambers as is.

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I think you're good making a more informed attempt at removing the old style nozzle plates and installing the newer style with your fresh injectors. I looked at the angles that come up against the pre-chamber on both styles heat shields and I can't see a obvious difference. Plus, there's Diesel911's post #16 in this thread that mentions changing over to the new style but does not mention swapping out pre-com chambers for a newer style. Seems likely and more economically sound to update the seals without changing the design of the pre-combustion chamber.

OTOH, I myself have installed injectors on top of these old style nozzle plates without trouble. Could buy you time, at least. And you could test for compression leakage past the nozzles post injector install by squirting soapy water around your injectors, with engine running. No bubbles = good to go.

I copied what I read in the Manual.

There was another service manual I looked in and it was the engine manual for OM 636 and OM 621 which I believe is an older engine. It showed the same what people are calling Top Hat heat shields that originally came with the engine and also tells you to replace them with the newer heat shields. Nothing about the need to change pre-chambers.

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84 300D, 82 Volvo 244Gl Diesel

The publishing date does not reflect when the stuff was written. On US Books you would look at the copyright date and it also may give dates when they were reprinted. The CD has no dates.

My Car is a 1984 and I pulled the Injectors in 2007. The Injectors appeared to have been the originals 27 years old with 198,000 miles on them (and worn out).
If you look at it from that perspective an Engine with the old Top Hat Nozzle Plates by 1980 could indeed have never had the Injectors pulled out for someone to changed to the heat shields. Reason enough to keep it in even the newest copy of the manual on an older engine.
Again looking at it from that perspective does not indicate they were using the Top Hat Nozzle Plates when they were building Engines in 1980.

Also my 1982 Volvo diesel uses the same new style Heat Shields as the Mercedes and there is no mention in any book I have see of the Nozzle Plates. I suspect it is the same with the VW Diesel Rabbits.

Attached is where I got the info on the bottom of the 2nd page and 3rd page.

Attached Files

07-230.pdf (64.3 KB, 98 views)

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84 300D, 82 Volvo 244Gl Diesel

Just wanted to drop a note to thank you guys for your thoughts - I've decided to try to remove the shields without damaging them. Will circle back if we're unsuccessful doing this.

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