Injector or Prechamber Compression Leak - PeachParts Mercedes-Benz Forum

hilda · #1 04-28-2011, 03:09 AM

1986 190d non-turbo 602

I had my injectors tested, and replaced a couple along with all new heat shields. I cleaned all surfaces well and put things back together. The engine runs great with good power and relatively little noise, except:
Cylinder 3 produces a compression leak through the threads of the injector body- between the injector and the injector holder. It doesn't leak around the outer threads of the holder, nor around the prechamber collar/head threads.
I switched injectors and heat shields, and retested several times using soapy water. Injectors that don't leak in other cylinders exhibit the same leak in this hole.
It's definitely compression, and definitely only between the injector and its holder. And definitely only on this cylinder with injectors that don't have this leak elsewhere.
Thank you for your expert help, this has me baffled!

vstech · #2 04-28-2011, 08:29 AM

get in there with a good light, and look over that prechamber.
odds are good it's cracked or damaged somehow.
do a search on bicycle puller for instructions on how to change the PC

leathermang · #3 04-28-2011, 10:28 AM

I do not have any manuals for you car.
But if it is like mine there are ONE TIME USE washers and things like that associated with those things....when you put it back together did you use brand new ones ?

vstech · #4 04-28-2011, 11:14 AM

Quote:

Originally Posted by leathermang

I do not have any manuals for you car.
But if it is like mine there are ONE TIME USE washers and things like that associated with those things....when you put it back together did you use brand new ones ?

Ahh, it's good to know I'm not the only one who skipps over reading sometimes...
re read his first sentence... (after his car description)

leathermang · #5 04-28-2011, 11:17 AM

My first sentence said " I do NOT have manuals for your car"...
so I do not know if heat shields are the only thing that might come under the heading of ' one time use ' in his situation....

vstech · #6 04-28-2011, 11:25 AM

ah. you're talking about after he started moving around the injectors for the test.

so... what else is disconnected in his diag procedure?

unless he removes the PC, I don't think there is anything else but the heat shields. and yes. they are one time use.
they need to be replaced each time you remove an injector.

leathermang · #7 04-28-2011, 11:32 AM

The title included ' precombustion chamber leak '... so I assumed that might have been taken out and put back in (?).... but I have admitted I am generically guessing in hopes of sparking his or others thoughts on the big picture...

babymog · #8 04-28-2011, 12:58 PM

The heat shield(s) could also be upside-down.

jt20 · #9 04-28-2011, 02:04 PM

Quote:

Originally Posted by hilda

1986 190d non-turbo 602

I had my injectors tested, and replaced a couple along with all new heat shields. I cleaned all surfaces well and put things back together.

Thank you for your expert help, this has me baffled!

you said you replaced 'a couple'... the old ones probably have a worn surface at the nozzle tip. Even cleaning will not correct a sealing issue.

There are 2 sizes of injector seals; one with a larger inner diameter than the other. Using the one with the larger diameter allows you to seal up used injectors that have eroded tips.

jt20 · #10 04-28-2011, 02:08 PM

as you see it in this picture, this is the wrong orientation for the seal when you put it in the head.

See how perfectly flat and machined that nozzle tip is on the injector on the left? Also, please elaborate more on where you think the leak is coming from.

Keep in mind, that a few bubbles springing up is not uncommon, and not a legitimate compression leak.

Zacharias · #11 04-28-2011, 02:39 PM

It's also possible, given how dark the recess can seem, to have an extra seal hiding down there, masquerading as the bottom of the hole.

Don't ask me how I spent hours finding that out (with exactly the symptoms you describe).

If you haven't already, examine the recess where the injector seal sits VERY carefully with a penlight or similar. In fact, it might be a good ideal to take a pick and gently probe just to be certain.

babymog · #12 04-28-2011, 07:37 PM

... or crank the engine with the injectors out, the heat shields will blow out quickly.

hilda · #13 04-29-2011, 01:50 AM

Thanks for the great response. I carefully cleaned the top of the prechamber until the metal was bright and clean. I made sure all carbon is cleaned off. I had plenty of light; I'm sure there is nothing else in there.

I picked up some more heat shields today from a very experienced Mercedes diesel guy who is also stumped.

It is leaking through the injector, not around it or around the retaining collar. What stumps us about the seals is that they work in the other cylinders.

I can't see any damage to the prechamber. The location of the leak means that the air is going through the center hole of the heat shield, past the inner lip where the heat shield is supposed to seal against the injector nozzle, and then up between the nozzle and injector body.

I like the idea of the alternative heat shields. Where do I source those?

Again, thank you for the great response.

hilda · #14 04-29-2011, 01:59 AM

Given the trouble and cost of buying a splined socket for my angled prechamber retainers, making a slide hammer attachment, yanking a prechamber, likely having to ream the seat, and buying a new prechamber, I may resort to some high-heat thread sealer and 120 lbs of torque if I can't find an answer.

What's the best way to check that inner heat shield-to-nozzle seal?

jt20 · #15 04-29-2011, 02:16 AM

Removing the prechamber is a bad idea. You will likely have worse sealing issues in different spots afterwards. Tightening up the prechamber is unlikely to result in any change without hammering the PC back in.

That is not issue, as you have described.

If I was you, I would powder the nozzle tip with carpenter's line chalk or something similar. Even high temp paint might be a good option.

Install the injector carefully, run the engine to operating temp.

pull the injector and check the tip.. the story should be told.