Pre chambers keep leaking OM603 - PeachParts Mercedes-Benz Forum

Dudernio · #1 03-18-2014, 02:59 PM

So I've removed and replaced these PC's three times now and still leaking- looking for where the problem could be. Cleaned everything thoroughly. Tried different torques within the specified range. Even tried installing the thin sealing rings, even though the length of PC tip projection is within spec. Any suggestions? Thread sealant on the collar nut maybe? Definitely leaking between the collar nut and female threads in the aluminum head.

The background information here: Installing a #22 head where it was previously a #14 head, and I'm using the old pre chambers from the 14 head. they appear to be in serviceable condition. Maybe something I'm overlooking here.

winmutt · #2 03-18-2014, 04:47 PM

The manual specifies using a special tool for redoing the seat. How bad is it leaking? Have you let them bake in a bit?

Dudernio · #3 03-18-2014, 06:12 PM

the seats (in the head) are in perfect condition, no pits, scratches and are flat and smooth. Only #4 & #6 leak... #4 is small but #6 is substantial enough that it's blowing diesel fuel out and hitting the underside of hood.

I looked again very closely today, now the fourth time removing everything and checking again.

I didn't know about letting them bake a while but did drive about 10 miles with the leaker and it still leaks.

Beginning to wonder if I'm using too much torque on the nuts and it's causing some warpage somewhere.

oldiesel · #4 03-18-2014, 07:44 PM

I am pretty sure that there is modification required to use the pre chambers from the 14 head in any of the later cylinder heads.
Do a search here as i believe this subject has come up before and one of the more experienced members did a good writeup about it.

Q: Are any modifications needed to bolt on the newer head?
A: In general, no. However the newer heads all came with different (angled/inclined) prechambers and injectors, and our 1986/87 engines have vertical injection. That means your vertical prechambers may not seat properly, requiring modifications to the old prechambers for them to seat properly. This only affects some newer heads, probably less than half - no way to tell until you get your replacement head, and do some measuring with the prechamber inserted. Yes, you can convert to the inclined/angled setup and elminate this problem. But that requires the newer prechambers, lock rings, injectors, AND glow plugs - then you need to bend the metal injection lines as well! Forget this option unless the used head includes all those parts.
From a writeup by GSXR Dave

Dudernio · #5 03-19-2014, 03:27 AM

found it here, thank you. OM603 - big compression leak at injectors/prechambers

Dudernio · #6 03-21-2014, 05:40 PM

It took a few trial and error passes at milling down the pre-chambers to finally get it right. Seems each bore in the head was slightly different. Some P/c needed no milling while others took a lot more to get it so they seated 100% I did install the medium size sealing rings as well. In this head exchange project (including rebuilding the turbo) going from a #14 to a 22, this was by far the most aggravating portion of the process but glad it's finally done. Thank you all for the good advice.

Shortsguy1 · #7 03-21-2014, 06:22 PM

Glad you got that resolved.

Could you clarify how you determined if you had milled enough? Were you able to tell they were seated correctly during install, or did you have to keep running the engine to test for leaks?

Also, do you have a specific thickness to the "medium size" seal rings that you used? EPC lists .3 mm, .6 mm, and 1.0mm, but then there are the really thick ones (2-3 mm) which come from the OM617 engines.

Thanks.

Diesel911 · #8 03-21-2014, 11:57 PM

Quote:

Originally Posted by Dudernio

It took a few trial and error passes at milling down the pre-chambers to finally get it right. Seems each bore in the head was slightly different. Some P/c needed no milling while others took a lot more to get it so they seated 100% I did install the medium size sealing rings as well. In this head exchange project (including rebuilding the turbo) going from a #14 to a 22, this was by far the most aggravating portion of the process but glad it's finally done. Thank you all for the good advice.

Did you measure the protrusion of the ends of the Rehabbers where they stick out of the Cylinder Head?

Dudernio · #9 03-22-2014, 03:51 PM

Before I installed the new (used) #22 head I did measure the the protrusions of the pre chamber tips, even without the sealing ring installed they were within specification by about 1.5-2.0 mm from what I recall. In milling down the prechamber, it would not affect the protrusion length my more than about .5 mm. what i found was the bore in the heads were not completely radiused. there were high spots. If i had known this prior to installing the head I would have had the holes re-bored on a drill press or something. After already installed on the engine modifying the pre-chambers seemed to be the easiest. It took three attempts, grinding down the pre chambers, reinstalling and running and observing for leaks. in sequence #6, #2, then #4 until no more leaks. I was very conservative on the amount removed each time. I used the .6 rings