OIL in a PRECHAMBER- cause and compression results? - PeachParts Mercedes-Benz Forum

blankenship · #1 08-21-2007, 04:03 PM

so, i've had a long thread about large amounts of grey/blue smoke, especially upon engine startup-
and did a compression test yesterday to help find some answers.

i noticed when I pulled the injectors that ONE of the prechambers (my #5) continues to be nastier than the rest.
there's a lot of black oil down inside there, and through the hole, which even spits up through onto the valve cover when cranking the engine with the injector removed.

also, there's 60 more P.S.I. compression on that one compared to any of my other 4 cylinders (it's 400, compared to 340 on the others). i'm imagining that this reading is the result of having oil in there, sealing it up?

WONDERING:
do you think this is the cause?
and why is there oil in that prechamber?

i've seem people venture to say that it could be from:
bad prechamber sealing ring,
bad piston ring,
bad valve stem seals,
cracked prechamber.

thoughts?

aklim · #2 08-21-2007, 04:08 PM

Well, if the oil is sealing it, there will be more compression. When you do a compression test, there is a dry test and then a wet test.

TwitchKitty · #3 08-22-2007, 10:49 AM

Quote:

Originally Posted by aklim

Well, if the oil is sealing it, there will be more compression. When you do a compression test, there is a dry test and then a wet test.

Wet test on a diesel can lead to combustion and flying parts and injury or death.

aklim · #4 08-22-2007, 10:52 AM

Quote:

Originally Posted by TwitchKitty

Wet test on a diesel can lead to combustion and flying parts and injury or death.

But the principle is the same. Oil seals the combustion chamber and hence the higher pressure reading.

blankenship · #5 08-22-2007, 12:12 PM

yeah, it's not PURPOSEFULLY a wet test

could it be a ring, with compression of 400 and very little blowby? or you're saying whatever residual oil is in there could be sealing the piston, leading to that high of a reading and behavior?

basically, i'm looking for advice now on WHAT ORDER to start investigating. if you think it could be PRECHAMBER related, let me know, as now's a good time to inverstigate that (as the injector is out, and i've got access for a couple days to the prechamber removal tools).

aklim · #6 08-21-2007, 04:10 PM

I'm thinking prechamber seal or maybe valve stem

blankenship · #7 08-21-2007, 06:30 PM

so, it's possible that a bad prechamber seal could do it?
but isn't the PC seal at the TOP of the prechamber underneath a lip? how would the oil get inside there, all the way down to where it's covering the ball?

or would you guess it would be a valve stem seal, or ? smoke's definitely a lot more significant at start-up, and there's very little blowby. i've had some high oil consumption, though.

aklim · #8 08-21-2007, 06:32 PM

Quote:

Originally Posted by blankenship

so, it's possible that a bad prechamber seal could do it?
but isn't the PC seal at the TOP of the prechamber underneath a lip? how would the oil get inside there, all the way down to where it's covering the ball?

or would you guess it would be a valve stem seal, or ? smoke's definitely a lot more significant at start-up, and there's very little blowby. i've had some high oil consumption, though.

Maybe it might have oil in the head and it seeps past the seal into the prechamber? I guess it is more unlikely than the valve stem.

That would make sense being a valve stem seal then.

kerry · #9 08-21-2007, 10:51 PM

How much oil could get down a valve stem? I suspect it wouldn't be enough to spit out thru the injector hole. Broken ring? Oil return hold plugged at back of head and oil running down the valve stem?

aklim · #10 08-21-2007, 11:15 PM

Quote:

Originally Posted by kerry edwards

How much oil could get down a valve stem? I suspect it wouldn't be enough to spit out thru the injector hole. Broken ring? Oil return hold plugged at back of head and oil running down the valve stem?

Well, enough to make smoke at startup.

vstech · #11 08-22-2007, 12:59 PM

that much oil in the system could be reducing the available space thus increasing the compression ratio, and bumping up the compression pressures. if you have oil squirting out of the injector hole, and it's not just dripping from the valve cover, you have a serious problem that can destroy the crank/rod/etc... my guess is something broken on the piston.

blankenship · #12 08-22-2007, 01:23 PM

well, to clarify, it's not that oil's just squirting everywhere...car's been parked,had the injectors removed for the compression test, and when performing the test on other cylinders, (with the injector removed from #5), there's some light "spray" coming up out of it from the force of the escaping air. could just be residual oil that had leaked down from the valve stem when the engine was parked, hot?

or somehow from a damaged PC or PC seal?

i'm posting a photo of the "bad/oily" PC on my #5,
and a shot of the #4 PC for comparison. see the black oily ball and whatnot down there?

blankenship · #13 08-23-2007, 11:39 AM

borrowed the special tools from a friend, and pulled the collars and PC's on a couple of my cylinders: (the #3 cylinder that had screwy collar threads, and the #5 cylinder that had oil in it).

ATTACHED are photos showing the results, condition, comparison. The #5 oily prechamber has A LOT of carbony, sludgy buildup and crust caked on it, and though i can't find any cracks in it, there is a good deal of "scaling" at the bottom tip of the prechamber, where bits of the metal are flaking off and distorting the shape.

i think the oil in #5 may be be mostly, if not totally, the cause/result of all the blue smoking i get at startup. can you guys speak to the condition, and whether either of the two prechambers need replacing, and what's causing this nastiness on #5?

vstech · #14 08-23-2007, 11:51 AM

bad valve guides, seals etc, cracked head, busted piston, broken ring. any number of things. it sounds like pulling the head and having it checked is next, look over the top of the piston while it's off. good luck.

bgkast · #15 08-23-2007, 01:22 PM

I would give the valve stem seals a shot before the head comes off!