Oil in pre-combustion chamber - PeachParts Mercedes-Benz Forum

CHAPP · #1 05-13-2003, 08:43 AM

I have oil leaking into #5 pre-combustion chamber on my '84 300SD. I have checked the valve seals and guides that were replaced 20K ago. I also did a compression test and leak down test with good results. The car runs great at highway speeds but blows blue smoke at a idle. When I remove the # 5 injector I see oil puddling up in there. Any suggestions?

Wasuchi · #2 05-13-2003, 10:39 AM

Does it idle rough? And are you sure it's oil and not Diesel? Just guessing but I would think a bad injector could cause Diesel to puddle in there....... but still run good at higher speeds.

leathermang · #3 05-13-2003, 11:02 AM

How does one check valve stem seals ?
What were the results of the compression test ?
What were the specifics of the leak down test ?
for instance.. what was the max pressure installed ?
what lower pressure was used for the timing to be taken ? How long did that take ?
What was the difference in time it took with oil installed in the cylinder ?

CHAPP · #4 05-13-2003, 11:38 AM

The valve seals looked fine... but I replaced them, after removing the springs etc. I got back 95-100% on the leakdown test, using 120psi. I did a cold compression test and the readings were all close...in the 300's.
The idle is rough, but runs strong highway speeds. The car starts as soon as you turn the key, but has blue smoke when idling unde 2 000 rpm. It is not diesel fuel in the chamber...it is motor oil.
Thanks for any ideas. I am hoping the seal in the chamber or the chamber itself has a problem.

leathermang · #5 05-13-2003, 12:46 PM

On a thread about leak down testing... we said we needed to start accumulating data on our cars to compare when someone else does a test...
So you used 120 lbs as a starting point ...
What lbs did you leak it to ? And how long did that take ?

CHAPP · #6 05-13-2003, 01:21 PM

I did all the hook-up's and basically what the mechanic told me what to do. We ran the test on each cyd. and valve for about 1-2 minutes. I would tell him what I had, and he keep telling me these were good numbers...he has had his leak down eq. for 15 years and is a triple ASE certified mechanic. We stayed at 100PSI . I just remembered the gauge only went to 100. I will have to talk to him and get the exact method we used...this was new to me.

michael cole · #7 05-13-2003, 02:07 PM

try a new valve cover gasket.on this engine oil leaks from the valve cover can work their way around the threads on the injector.the same goes for the diesel leaks from the rubber return lines on your injectors.beleive me i visited both these scenarios

#8 05-14-2003, 01:05 AM

I doubt that the problem lies with the prechamber itself. There is no connection between them and the lubrication system. I know you say that the compression and leakdown tests posted well. I would wonder if there isn't a headgasket problem that would be sealing under pressure, but allowing oil into the cylinder during the intake stroke? This should be considered only after all other options have panned out.

CHAPP · #9 05-14-2003, 08:42 AM

I have a new valve covern gasket on it and had no oil leaks. I also have no diesel leaks. But...maybe the head gasket could be it? I will do another compression test...I am thinking it could be a oil ring and still have good compression.

CHAPP · #10 05-15-2003, 01:19 PM

Any other ideas on this? I don't want to take it apart unless I have to.