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  #1  
Old 08-13-2002, 11:25 AM
Kent300D
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injector heat shields for a 300D - are they necessary?

My W115 1976 300D (135,000 miles) started nailing badly so I decided to replace the original (as far as I know) injectors.

When I removed the old injectors I did NOT find any heat shields.

When I look into the threaded receptacle for an injector I see a 3/8" (or so) hole in the sloped bottom of the receptacle but no heat shield. The new heat shields that came with the rebuilds do not look like what I see at the bottom of the injector receptacle.

Is the bottom of the threaded receptacle actually the heat shield, and I'm not distinguighing the bottom of the receptacle from the heat shield?

I'd hate to start tearing up the bottom of the injector receptacle thinking it was a heat shield when someone failed to reinstall the heat shields as some earlier time (however, I have all the repair records for the car and none suggest any work on or involving the injectors).

Did the W115 76 300D come with injector heat shields?

Would it be better to install the new heat shields regardless?

Robert

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  #2  
Old 08-13-2002, 01:29 PM
surfblau's Avatar
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Join Date: Feb 2002
Location: san francisco - immer kalt, immer windig, I want to move
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my experience

When I opened up my 617 injectors because of nailing issues, I found that most of the heat shields were pretty coked up, but instead of having no heat shields, one of my injectors had two heat shields.

I removed the extra shield, and replaced all the rest with new (clean) shields and the nailing went away.

I am guessing that MB designed the heat shields to also provide an easy way to remove carbon from the prechamber area without having to clean more of the injector face. Just a guess.

In any case, I would go look at the factory manual that discusses injector R/R for your engine. That should make it clear whether you need shields or not.
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  #3  
Old 08-13-2002, 03:01 PM
Kent300D
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Surfblau,

Thanks for responding.

The manual calls for heat shields...but I'd swear that their were NO heat shields with the original injectors.

Maybe someone got sloppy at MB when the car was built - perhaps the same worker who put 2 shields in with one of your injectors! Or maybe the independent my family used removed the injectors and forgot to put back the heat shields (I've come to realize the more I work on the car that the independent my family used has given new meaning to the term "gerryriggeg").

I put the heat shields in, reassembled everything, and fired the 300D up.

The nailing is gone, the idle is MUCH smoother, and there are no leaks...looks like I did it right!

So, I either have one or two shields with each injector...either way it appears to work.

Robert



I just
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  #4  
Old 08-13-2002, 03:43 PM
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Question 617.912?

Seal ring, MB # 601 017 00 60 is shown in the parts diagram! Good Luck!
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  #5  
Old 08-13-2002, 08:38 PM
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New style seals are called "heat shields" and look sorta like washer. Old style seals go into the hole in the pre-chamber and the injector nozzles seat on them. They are VERY difficult to remove.

What you have is both in place, and if you don't have any problems, leave them alone. I have one in the 220D -- couldn't get it out, so I left it. I had compression leak problems with the new one on top of it. Check for oily stuff collecting around the injectors -- this will be unburned fuel. If you get bubbles in it while running, you need to remove the heat shields and use the old seals that are still in there, or put a wood screw into them and pull them out.

Peter
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  #6  
Old 08-13-2002, 09:32 PM
Kent300D
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Peter,

Thanks for the very valuable information...I know I didn't see anything that looked like the new heat shields.

Is the old seal composed of just the raised part of the bottom of the chamber - ~ 1/2" in diameter (about the diameter of the injector nozzle), with ~ 3/8" hole in the middle, and slightly raised.

Is it likely that having a second seal/shield will interfere with the injector's spray pattern now or sometime later?

What roadblocks would I run into if I decided to try and remove the old seals - e.g., is there a good chance I could crack something important...or will the seals just pop out harmlessly once enough torque is applied to remove them?

Is the use of a small slide hammer a good way to remove the seals?

Thanks for your help.

Robert
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  #7  
Old 08-14-2002, 12:38 AM
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Kent300D,

When I changed the injector nozzles for the first time on my 1975 240D I got the new seals/heat shields woith the nozzles and felt obliged to remove the old ones to put the new ones in there. The original ones were small diameter washer like things with a cylindrical extension, like a tube, about a quarter inch long, in the center, around the hole. The central cylindrical section gets pretty well stuck in the hole in the bottom of the injector housing of the prechamber. I got a tool at Sears that I still have and have never used again, that looks like a phillips head screwdriver but with a threaded, tapered end on it. I jammed this thing into the hole in the center and then twisted it to thread it into the seal, and once it had a good bite, I pulled it out with a sharp yank. Each one came out, and I probably still have them in the basement somewhere. My biggest problem after that was figuring out which way to put the new ones in as they are not the same on each side. I do not recall the answer to that anymore or I would volunteer it now. Anyway, anything that you can thread into the hole will work to pull the old ones out. Good Luck, Jim
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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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  #8  
Old 08-16-2002, 01:08 PM
Kent300D
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Jim,

Do you agree with Peter (psfred) that I should leave the old seals in as long as everything works properly and there are no leaks?

Or do you think there will likely be problems down the road with this approach?

So far (~150 miles) everything seems okay.

Thanks again for your help,

Robert
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  #9  
Old 08-16-2002, 04:02 PM
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Join Date: Jun 2002
Posts: 296
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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  #10  
Old 08-16-2002, 04:15 PM
Kent300D
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Beagle,

Thanks for your reply.

I have a 1976 W115 300D with the 617.910 engine - you are describing a 1977 W123 300D (617.912 engine). I don't know the extent of the overlap when it comes to heat shields and injectors, but I wouldn't be surprised if they used the same equipment. Do you know?

Nonetheless, my basic question remains the same - if everything works properly and there is no leakage, is it a good idea to leave what I've done (new shields on top of old seals) alone?

The car has never run better than it does right now.

Robert
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  #11  
Old 08-16-2002, 05:42 PM
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.When I look into the threaded receptacle for an injector I see a 3/8" (or so) hole in the sloped bottom of the receptacle but no heat shield.

Robert
From what you describe above it would seem to me that you had no seals in when you removed your injectors. The seal seats on a 20º cone with a 10mm Dia hole as you describe. My guess is that you are assembled correctly with one seal. You would surely have had problems with leaks using 2 seals.
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  #12  
Old 08-16-2002, 06:14 PM
Kent300D
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Beagle,

Thanks for the reply.

My gut feeling is that Jim Smith is right...the old "seals" are still in there - they just don't look anything like the new "shields". And as psfred noted, I should just leave well enough alone as long as things are working properly and there are no leaks.

The manual makes reference to NOT using the old-type seals when replacing the originals - it says to use the newer "resilient" shields only.

If Jim is right, the older seals sit almost flush with the bottom of the chamber (according to Jim's description, a part of the older seals actually goes through the hole in the chamber). The new shields wouldn't protrude through the hole in the chamber as far as I can tell (but I may be wrong about this).

I think that because the old seals sit so low in the chamber and the new shields have a concave bottom, the old seals and new shields do not really interfere with each other (I got lucky?).

Alternatively, someone may have removed the injectors at some time in the past, removed the seals, and then failed to replace them. This is VERY unlikely as I have the entire repair history of this car (it's been in my family since bought new), and there is nothing that suggests any repair work that would have required removal of the injectors, needless the seals.

So, MB never put seals in my 300D or the seals were removed and not replaced or I have 2 (1 old and 1 new seal) in each chamber.

Whichever way, things are working VERY well, and I think I'll leave it alone unless something happens or someone suggests a good reason for going back in and extracting the older seals (once again, if there ever were any older seals!).

What do you think?

Robert
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  #13  
Old 08-20-2002, 02:18 AM
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Robert,

Sorry I was off line for a week on a trip. Just got back today and started looking at some of the threads to check progress.

The old seals sit in the bottom of the prechamber, and are a different color (darker) than the prechamber. They are nothing like the new ones that look more like a shaped quarter or something of that size. The originals were shaped like a top hat (that was open across the top of the top hat), and put into the prechamber with the top of the hat down, into the hole in the center of the prechamber. The "rim" of the top hat was pretty small, and the outside diameter of the rim was less than half that of the new shields. This is all from memory as the manual is useless in this area. It just says take the old ones out and put new ones in. The drawing of the engine cross section shows the old ones though, and they bear on the injector nozzle face, in fact they are the same outside diameter as the nozzle of the injector to give you an idea of how much smaller they are than the new ones. They are called "nozzle plates" in the manual, not seals.

So, if you have both in there I would expect your injectors are sticking out higher than they should, and if you are not leaking by it is luck. The injector seals to the prechamber just below the threaded section of the injector, I believe, and that injector body shoulder will not bear down on the mating surface if there is something holding it up underneath. So you are sealing on the nozzle plates, not the design location.

I hope this is not more confusing than it was before I decided to clarify the situation. If I had no trouble, and the injectors seemed sealed, I might wait until a day when I was really bored, and then I would take one out to look. If it had two pieces in there I would take them all out and put new, unused ones of the later design back in, and call it a day. Good luck, Jim
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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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  #14  
Old 09-20-2002, 12:18 AM
Kent300D
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I had some spare time today so I decided to go fishing for the old heat shields.

This time when I took out the injectors, I could clearly see the old "top hat" like heat shields - they had been bombarded with diesel fuel for the last several weeks and they stood out like a sore thumb (they really blended into the bottom of the prechamber the first time I changed the injectors).

After fiddling around for about 1/2 hour trying to get the first old heat shield out, I finally devised the right tool and they came out rather easily.

Popped in the new shields and the injectors - NO leaks...and off I went.

I noticed 2 things: 1) the car was peppier - could it be that the spray pattern is likely better now that the injector nozzles sit the MB-designed distance from the hole in the bottom of the prechamber??? and 2) the car seems to shift more smoothly - got me on this one!!!

These 2 observations are based on about 10 miles of driving - I'll report back after I put more mileage on the car (especially looking forward to seeing if the mpg improves).

Thank you all for all your help...I really could not have done this without your help and encouragement,

Robert

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