OM606 Combustion Leak at Injector
 

This is a 1999 E300 with about 260k miles. The radiator cracked and quickly dumped the coolant and the engine temp spiked. When I got the car back home I started it to check for damage and find there is a gas leak coming from the location of the #6 injector. I made a tool to remove the injector and don't see anything unusual. My plan is to do a compression test and, probably, a leak down test. I guess I will have to get the special tool to remove the pre-chamber which I expect will have to be removed. Any thoughts on what might be going on? My fear is a crack. but I can't see one as of yet.

Answer
 

My best guess = warped or cracked cylinder head.

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I would try the easy thing first, replace the injector heat shield and properly torque the injector back down to see if it's any better.

The heat shield looks OK. No apparent heat distress or distortion. My plan is to put it back together and do a compression test and see what it tells me.

glow plugs
 

Remember that the glow plugs need to come out before you take out the prechambers.

I don't think you can see distortion or distress on a used heat shield. They are a one time use item - kind of like the oil drain plug crush washer.

If you are going to put the Injector back in and run it you can get a genreic pump typ spray bottle and 1 quart of Water mixed with 1/4 cup of Dawn Dish Soap (this makes a mix that Kids use to blow bubbles in preschool).

Spray it onto a cold Engine and start the Engine. I you have any sort of gass leak under pressure the stuff will bubble and show where the leak is.

I installed the injector in # 6 and removed the glow plug. I then applied air to the cylinder. I could see the air leaking through the location slot on the pre-chamber. Is there a seal under there that could be blown out?

I finally got the tools together to pull the pre-chamber. I didn't find anything dramatic under it but, I don't know what it is supposed to look like. I see an area on the seal surface in the head that might be a leak source but can't detect any roughness by running a probe over it. There is a fair amount of carbon in the cavity in the head that is going to be hard to remove without making a mess. I note that there are some repair rings that can be fitted under the PC but, I don't see any guidance on how they are applied. I would presume the surface would get machined down to accommodate the repair ring. Any one know anything about that?

When the Aluminum Heads warp you cannot always see the defect.

There is a special expensive tool to go in and cut a new seat in the Cylinder head. You need to follow the instructions in the Mercedes Service Manual on the use of the Tool and picking the size of prechamber sealing ring.

You need to be carful with cutting the new seat as the end of the Prechamber needs to be within a certain distance from the top of the Piston. If the Seat is cut too much and the wrong Seal Ring is chosen and the Prechamber end extends too far the Piston will hit the prechamber.

If the Prechamer is too high up the combustion gasses are going to spray on the wrong parts and over time will burn into the metal.

If you can access it there is a free Manual on the Mercedes EPC or another member can supply the info.

Thanks. That is pretty much what I was expecting. I signed on to Alldata for this car but there is absolutely no guidance on doing this repair. Maybe I'm missing something. I don't see where to obtain the tool or any guidance on its use. There would have to be some measurements to establish a depth of cut for a particular repair ring. Anybody know where I might find this information?

You will need to search the do-it-yourself in the Repair Links to see what others have done.
If you had the instructions on how to use the Tool you would find before you start you would take a measurement of the inner part of the Tool to the outer part of the Tool. That tells you where you start from.

When you cut with the Tool one of the parts of the Tool sinks lower and you measure that distance it sunk and subtract from the original distance and that tells you how deep you cut.

Besides having the expensive tool you need something like a Dial Indicator or Depth Micrometer to measure the Tool.

As far as I know there is no cutter tool in the tool rental.

I signed up on Startek EPC and have searched through there. I can see the repair seal rings but haven't found the tool nor the instructions for its use. I also have dug around and searched the DIY sections to no avail. This is apparently not a common issue, as I can imagine. I'm at the point of calling my local Indie that I trust. I just don't like to bother him about things like this. Unfortunately, I'm stuck and can't see where the solution lies.

Did you found out the issue?

Number 5 prechamber is leaking where the grove is, it seems anyway.
I inserted a 1mm shim ( the only one available from merc at that time) and torque it to 130nm, same, the gases are blowing.
I use a breaker bar and did another quarter turn, hoping it'll quash the seal, nope, same.
I do not know what to do :(


Thanks.
Olivier

Did you ever have an outcome for this? I’m pretty sure my replacement prechamber is leaking on my 602.

what was the shim made of?