Pre-Chamber Ball Came Loose

[gmog220d]

1974 240D, W115, OM616.916

I recently moved back to New Mexico from Utah. As part of the process I drove the '74 from Salt Lake City to Albuquerque, about 600 miles. During the trip the car started nailing, and it got worse quickly in the last 30 miles. When I got home I cracked the fuel lines and isolated #4 as the culprit. I've experienced nailing before but not like this. It was nailing at high RPM, under power while going down the road. I did not notice a decrease in power, and the engine did not over heat.

Some history: 3 years ago, before moving to Salt Lake and driving the car there, I had all four injectors rebuilt by a local ABQ shop I trust, Central Motive Power. Looking at the receipt it is not stated explicitly that nozzles were replaced, but I assume they were since the total for all 4 injectors was $340. I also re-timed the cam using a offset key, and re-set injection timing to compensate for a little bit of chain stretch. Then we moved to Utah, and the car did fine during that 600 mile trip and also for the little bit of use it got in SLC. It ended up sitting in storage for most of our time there, driven only 500 miles or so during the 3 years. I used diesel stabilizer and Biobor in the fuel to prevent problems related to fuel storage.

So today I spent a little time taking things apart to see if anything was obviously wrong. I removed the injector and found that the nozzle needle's tip was broken off:



I looked down into the pre-chamber to check on the ball, and sure enough it was busted off and floating around in there. I also noticed that the tip of the chamber was bulging out a little:


And here is the tip of the glow plug (glow system converted to pencil type plugs):


At this point I assume the nozzle needle broke off allowing fuel into the chamber out of time thus burning up the ball and glow plug and causing the chamber tip to bulge. Replacing the damaged parts with good ones should get the engine going again, right?

I need a pre-chamber - does anybody have one laying around that I could purchase? It's the flat tipped chamber for NA engines I need, not the rounded tip like you find in the 617 turbos.

Part of me also wonders what else could be at play here. Injector damaged by water in fuel during storage? Did I set injection timing too far advanced (I've set IP timing before with no troubles)? Anything else I should be looking into here?

Thanks!

[MB140300SD]

While you have the injector out I would probably check the compresson to make sure it did not hole a piston or something. Did it seem like it was only running on 3 cylinders or did it run normal but just have the nailing.

[gmog220d]

Originally Posted by MB140300SD

While you have the injector out I would probably check the compresson to make sure it did not hole a piston or something. Did it seem like it was only running on 3 cylinders or did it run normal but just have the nailing.

I'll have to borrow, buy or rent a tool set for checking compression but that is a good idea. The engine ran fine despite the nailing. No noticeable loss of power and no smoke, no loss of engine oil. After pulling the pre-chamber I looked down onto the piston top and did not detect any damage where I could see.

[Diesel911]

You could remove the old Nozzle and see if it is a Bosch Germany or a Bosch India Nozzle and you will know if they replaced the Nozzles or not.

[gmog220d]

Originally Posted by Diesel911

You could remove the old Nozzle and see if it is a Bosch Germany or a Bosch India Nozzle and you will know if they replaced the Nozzles or not.

Are they marked? I've never gotten myself into the guts of an injector. I'll check it out. Thanks for the suggestion.

[Diesel911]

Originally Posted by gmog220d

Are they marked? I've never gotten myself into the guts of an injector. I'll check it out. Thanks for the suggestion.

The Nozzles are marked around the top lip. Made in France is also good.

The picture is just to show where the info is located. You need to remove the Nozzle Nut to get the Nozzle out.

In one pic the square box has the 2 parts of the Nozzle and the green arrow points to a part that if you don't get it installed in the correct orientation will break off part of the Nozzle.

[gmog220d]

Originally Posted by Diesel911

The Nozzles are marked around the top lip. Made in France is also good.

The picture is just to show where the info is located. You need to remove the Nozzle Nut to get the Nozzle out.

In one pic the square box has the 2 parts of the Nozzle and the green arrow points to a part that if you don't get it installed in the correct orientation will break off part of the Nozzle.

We were typing at the same time! Thanks for your response. I'm taking the injector down to the shop this morning to have it rebuilt again.

RE: Indian nozzles - I had all 6 injectors in the '96 rebuilt with Indian nozzles a year or so back. I've not had any trouble with them. In fact, the car runs really well. But, I know, it only takes one bad one to ruin your day (or your pre-chamber).

[Diesel911]

Originally Posted by gmog220d

We were typing at the same time! Thanks for your response. I'm taking the injector down to the shop this morning to have it rebuilt again.

RE: Indian nozzles - I had all 6 injectors in the '96 rebuilt with Indian nozzles a year or so back. I've not had any trouble with them. In fact, the car runs really well. But, I know, it only takes one bad one to ruin your day (or your pre-chamber).

I forgot to mention that there is different types of Prechambers. There is a number on the flange of the prechamber that needs to match up with the replacement one.

[gmog220d]

I took the injector apart this morning and found that the nozzle is a Bosch India unit. Got about 2000 miles out of it, as well as a bum pre-chamber and glow plug.

Did the busted needle cause all of this? Or was there some other factor involved in the needle tip breaking off?

Found used pre-chambers for sale and just ordered one from our friend Kent.

[NZScott]

Just a couple notes during my lunch break...

Running lean in a diesel means running cooler temps, its the opposite of a petrol engine (unless its running lean of peak)

The prechambers changed during a few years for emissions reasons I believe, then changed back (I think, don't really know) so that will be why there is a difference. It's not a heat shield

[gmog220d]

Originally Posted by NZScott

Running lean in a diesel means running cooler temps, its the opposite of a petrol engine (unless its running lean of peak)

With respect, the statement assumes the IP governor has not been putzed with. As I understand it, with pneumatically governed IPs, altering the position of the diaphragm/fuel rack by changing tension of the governor spring results in a change in fuel delivered in relation to the amount of air coming through the intake. In my case the bias was lean.

Originally Posted by NZScott

The prechambers changed during a few years for emissions reasons I believe, then changed back (I think, don't really know) so that will be why there is a difference. It's not a heat shield

I only know what I've seen with my own eyes.

My '74 240D came to me with with all four of the pre-chambers having that steel disc in them, and no removable heat shields like we are familiar with. I drove it for a while before getting into the injection system. When I did get around to removing the injectors I noticed the lack of removable heat shield and also noticed that the nozzles sealed up against those discs just fine, no signs of compression leakage. Still, I swapped in the set of "MADE IN GERMANY" chambers I had on the shelf so I could use the removable heat shields as usual.

I also pulled injectors and pre-chambers from a U-Pull engine that had these steel discs in them. The injectors were installed using the usual removable heat shields on top of the steel discs. After pulling the injectors I found excess carbon in the space between the nozzles and chambers. The removable heat shields had to be dug out of the carbon mess. Seemed to me they weren't sealing very well when used in conjunction with the riveted in steel discs.

I can't be the only fellow to have stumbled onto these oddball S&K pre-chambers . . .

[NZScott]

Originally Posted by gmog220d

With respect, the statement assumes the IP governor has not been putzed with. As I understand it, with pneumatically governed IPs, altering the position of the diaphragm/fuel rack by changing tension of the governor spring results in a change in fuel delivered in relation to the amount of air coming through the intake. In my case the bias was lean.




I only know what I've seen with my own eyes.

My '74 240D came to me with with all four of the pre-chambers having that steel disc in them, and no removable heat shields like we are familiar with. I drove it for a while before getting into the injection system. When I did get around to removing the injectors I noticed the lack of removable heat shield and also noticed that the nozzles sealed up against those discs just fine, no signs of compression leakage. Still, I swapped in the set of "MADE IN GERMANY" chambers I had on the shelf so I could use the removable heat shields as usual.

I also pulled injectors and pre-chambers from a U-Pull engine that had these steel discs in them. The injectors were installed using the usual removable heat shields on top of the steel discs. After pulling the injectors I found excess carbon in the space between the nozzles and chambers. The removable heat shields had to be dug out of the carbon mess. Seemed to me they weren't sealing very well when used in conjunction with the riveted in steel discs.

I can't be the only fellow to have stumbled onto these oddball S&K pre-chambers . . .

I think you just missed my point in that burning too much fuel relative to air in a diesel causes higher temps...you say its running lean but say its been hot...the two are opposites. But yes, the IP could be out of whack to cause it.


These prechambers are probably well known about in other circles, its a shame I can't read German as their forums would probably shed some light on these interesting prechambers. The other ones I mentioned were actually much later now I think of it, as your ones are the old blunt end design not the round tipped ones.

[Garagefull]

My schedule did not allow for me to do some work last year on one of my diesels.I took it to a mechanic that I have known for years. He made the same statement about lean. A gasoline engine uses unburnt fuel to remove heat. Running lean causes temperatures to skyrocket. With this high temperature, you will experience detonation which is the fuel expanding too early in relation to top dead center. In a diesel engine, the fuel is not added until just before top dead center. So another words it's not hanging around in the cylinder and getting lit off early due to detonation because it's not been injected yet. That is what allows the extreme cylinder pressures inherent to a diesel. The fuel simply has not been injected yet, and cannot detonate.

[barry12345]

Wrong fuel in a fuel vendors tanks is not impossible. If possible fuel at busy truck stops or at least a fairly high volume sales place. A gas diesel fuel mixture could have done this.


My issue with smaller volume fuel sellers. Many are supplied with non dedicated tankers. You thought you had more power is almost a giveaway.


Although there is no certainty some fuel issue was a possibility.

[Maximan1]

I pulled a set of 4 S&K prechambers out of my '79 240D. After I cleaned them in an ultrasonic cleaner, it doesn't look like the bottom disc is riveted in. I can't really see any kind of seam on mine.

I did run the heat shields as well, with no real issues to speak of. Heat shields were in when I pulled my old injectors out, judging by the rest of the car I would not be surprised if the injectors had never been out before.