Dear Inzgary...
That's interesting...can you elaborate on that? How many instances has that ball come loose have you heard about? That certainly could have trashed the glow plug and caused a lot of debris...a ball rattling around in the precombustion chamber would pelt everything...come to think of it, the injector face and pintle were fine, and so I would expect to see some damage to that surface. But while this failure may not have been due to a ball coming loose, I would be interested to know more about what you've heard. It looks like the support for that ball is interference fit into the body of the chamber I think I one side...doing this from memory. I think its purpose is to break up the injector aerosol into smaller sub micron droplets to improve combustion...not sure if all turbos had this...anyone know?

Here is one similar instance I found: Pre-Chamber Ball Came Loose
That was a 220 so the non turbos also had the same pre chamber design. Add going 70 mph down the highway and the pressures going in and out of the pre chamber are likely high enough to blow the tip away. My theory is that is caused by a streaming injector. The metal ball starts burning, breaks loose, and rattles around ultimately creating a check valve of the pre chamber.

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1984 300D Turbo 200K

Here are the pics of the reference Inzgary refered to...very interesting how the ball pounded the end of the precombustion chamber...my injector sprayed well and the pintle was in place, but I suppose removing and cleaning the chamber at some point is a good idea, but they are a real bear to remove...you need a special tool (I got mine from Kent) and need to use a slide hammer...any one have any thoughts on what could make a dispersion ball in a prechamber come loose?

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Thanks for posting this. The valve failure does NOT look like a burn failure - they tend to lose a sort of a slice of pizza kind of missing section. I agree that this was a case of the valve contacting something hard. Probably ought to change out the ones on Mutt's engine. Where did you get your GPs?


Dan

When you say original glow plugs, are you referring to the pencil type?



Assuming it was one of the pencil type glow plugs that failed, it makes me consider the pre-chamber design from the original engineer's perspective. I wonder if they would have designed the prechamber in a different way if they had originally used pencil type glow plugs? Seems that this problem would not have occurred with loop type. What happens in a modern diesel if the pencil glow plug disintegrates in such a way?


-Henry C.

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1976 Mercedes-Benz 300D, Colorado Beige / Mahogany
www.hmclever.com

The damage is clearly a case of an oil filter that is too small being installed by those quick oil change idiots See post 43

https://www.peachparts.com/shopforum/diesel-discussion/313655-how-could-my-om617-compromised-so-quickly.html

Hi Dan, Cleeves....
The glow plugs were from Kent at ************** and were the pencil type...the originals were pencil and Bosch. If you note the shiny scrape across the exhaust valve it is clear it was definitely hit by a good size chunk of metal...the top of the piston was imbedded by many metal fragments...I tried to use an air hose to blow it off...no luck...could feel the debris buried in the surface...

I don't agree with assessments that a streaming fuel injector could do this. Water jets cut with a minimum of 40,000PSI up to 100,000 PSI, and use an abrasive to cut metal and stone. These injectors nominally are around 2000 PSI, so cutting through a preinjectors housing or a glow plug is hard for me to believe.

Cyclic heating of glow plugs, which really do glow quite brightly, which are suddenly quenched by a spray of diesel, will undergo a heck of a hot of expansion and contraction, so scaling over time would not surprise me. Look at the pics...

Because new glow plugs are so cheap and easy to install, I think replacement every 100K along with injectors would be prudent. A set of injectors if you don't want to rebuild your own are like $500, glow plugs like $50-60 tops. I wish we could find early Mercedes engineering test data they ran when trying to optimize the prechamber size, ball, tip hole size and number, etc. It would be interesting to learn what they found on pressure rise time, peak pressures, etc and how what affected what. I'm sure some of those engineers are still alive and there must be some discussion out there. This is a strong engine and failure modes like this are a fluke, but there must be a clear explanation we can all avoid. For all I know one of the components may have been outsourced by Bosch to another country where the QC was fudged. I had a 300SE that had a soft cam due to poor surface hardening by the vendor. And Mercedes does make engineering mistakes...remember when someone decided a single row timing chain was OK in lieu of double chains that served so well for decades?

I'd like to know how many others have seen a prechamber ball come loose and why. Buying new and replacing them on a whim may be no better than keeping the originals since we don't know where new parts are being sourced from and private labeled these days...China??

I buy the idea that excessive boost pressure could result in high combustion temps and could cook things. It makes sense to check the overboost control on any OM617.

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I wondered about gas too. It is easy to do. I have done it three times myself. One of my daughters ruined a brand new motor by doing it.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Hi PreferVintage

A badly spraying injector will melt the ball inside the prechamber and here's why:

When mercedes went from vertical to angular injection on the OM603 they had to make the ball from a more heat resistant material.

source is page 2 of this pdf:

http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/01-416.pdf

Before it was all self service. I told the daughter to always fuel the diesel herself. Well you know the rest of the story.

I repaired the generator and got several cans of high test as we had no power after the storm. Had to drive over to the next province to get it. Not far though. The power was not expected to be restored for days. I was really concerned about the large freezer primarily.

The power came back on very early. The wife asked what was I going to do with all the gas? I had forgotten as of a few days ago we are not driving any gas cars now.

She had figured that out apparently. As she knows gas goes into cars. She really caught me. So I was in no mental condition to say we can burn the house.

It appears Kent at mercedes source have a new video concerning a 300D he calls 'Digby' in his video number 4, show a precombustion chamber with the tip blown off...just like mine looked...it will be interesting to see his next video and what the piston and cylinder walls look like, and what he thinks happened...

This is a pic of the prechamber shown by Kent on Mercedes Source in his 'Operation Save Digby Part 4' video on You Tube...it looks just like what happened to mine...

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part 5 is out and this is his conclusion:


-injector/running hot was the cause
-it's rare
-his cylinder wall looks good and it still has compression

https://www.youtube.com/watch?v=JGfIyPwCMRQ

Thanks Christuna for the update on the new video. I think Kent was speculating too much here, and he was just very lucky the piston and valve(s) weren't damaged by the debris. I cut the prechamber lengthwise and acid etched, and examination of the grain structure revealed the tip was blown off...no metallurgical indication of overheating...grain structure was uniform the rest of the piece...only stress fractures / dislocations near the tip. See attached photo of normal uniform grain structure. His statement that overheating made the tip brittle and crystalline makes no sense...metals inherently have a crystalline structure. For the temperature extremes he mentions, the chamber would have to have been repeated cold quenched, which couldn't happen in a running engine to the extremes required. There is the possibility however that there was a QC deficiency with whomever made the prechambers for MB. I once had to replace a soft cam on a 300SE I had because the surface wasn't properly hardened, so vendors for MB do screw up. I still think original glow plugs after tens of thousands of cycles can create scale which collects in the tip. (My glow plug tip was a mess on number 5, and it had scale...but I note that could have happened with the ball flying about before or after chamber failure). Reading up on some of the design changes MB made over the years, one can see how they were trying to both deflect injector spray plume to break up the droplets into smaller fractions to increase surface area and thus combustion efficiency, and position holes in the tip to enhance air flow vorticity in the prechamber to aid in fuel-air mixing just prior to combustion. With all that swirling about, it's just dumb luck to have enough 'stuff' collect at just the right time to plug enough holes so the pressure rise exceeds the tensile strength of the prechamber tip. Indeed an odd ball fluke event. I just never could have foreseen this failure coming. All was running well on this car, no injector nailing, I had all maintenance records, and it was last owned by the proverbial little old lady who was nearly 90 when the car was sold, so the vehicle was not abused, and only run on diesel. In the future, if I buy another diesel, the first thing I'll do after getting it home is waste no time and pull all injectors, and inspect the prechambers to look for the ball in place, change out the glow plugs, and rebuild injectors/balance. (I was in the process of having Monarks ready when my failure occurred). I should note the injector on my failed chamber was spraying well and had a pop pressure of 1900 PSI...I wish I could blame a leaking or streaming injector on this failure. Doing injectors and glow plugs, plus valve adjustment is inexpensive enough and easy enough anyone taking their time can do themselves. I really hope no one ever has to experience this kind of event, hence my trying to share as much as I can. It was a pain to find out the engine was toast, pull it, find another engine, and put that in...a $6K expense total not including time that may, I say may, been due to a $10 defective glow plug and/or prechamber.

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Yes.

I wonder if MB has anything to say about this failure.


1989 and older M103 engine can suffer from cam wear and I think in this case it was MB trying to save money not a vendor.