OM603 - big compression leak at injectors/prechambers - PeachParts Mercedes-Benz Forum

gsxr · #1 03-10-2002, 10:59 PM

Hello again,

Well, I finally got my new head installed, and got everything back together, ready to fire up for the first time. I started cranking and heard a rhythmic "chuff chuff chuff" noise. Uh-oh. I stopped, then had my wife crank over some more while I held down the "stop" lever on the I/P to figure out the source. I'm getting compression blowby past the prechambers and/or injectors, believe it or not! I can feel a very distinct puff of air over each injector as the engine cranks and each cylinder hits its compression stroke.

I cleaned up the old prechambers before installing them in the new head, the mounting bore was clean, and I installed new nozzle seals underneath the freshly rebuilt injectors. Everything was torqued to spec and the threaded ring was oiled as per the service manual instructions. I put the nozzle seals in conical side down, flat side to the injector.

At this point I'm at a loss. Any ideas? There's only 3 parts and a seal involved, what could I have done wrong? Or what part could be responsible?

Help!

engatwork · #2 03-11-2002, 09:52 AM

Flat is supposed to go against the engine head - sounds like they are backward.

gsxr · #3 03-11-2002, 10:12 AM

Are you sure about that? The bottom of the injector is flat, the sealing face of the prechamber appears to be conical. And I'm pretty sure the old ones were in the same way...

gsxr · #4 03-11-2002, 02:12 PM

Hi all,

I got this from a member of the MBZ.org diesel email list:

Hi Dave-

I went through the same thing when I replaced the head on my 603 (87 SDL). I bought new pre-chambers also. The problem was that the bottom of the pre-chambers struck the bottom of the bore before sealing on the top lip. Matrix Motors was very helpful in describing the cause of the problem and recommendations. I simply ground off a little of the bottom of the pre-camber and added a shim (MB part) and it solved the problem. I probably did not need the shim, but I did them both at the same time. I did not need new pre-chambers either.

Dale Weidemann
Madison, WI
300SDL
300SD

This is bizarre. Has anyone else experienced this when installing a new OM603 head?

Regards,

engatwork · #5 03-11-2002, 03:17 PM

I was thinking about the 1985 300D which is the cast iron head.

gsxr · #6 03-11-2002, 03:53 PM

More from Dale. I'm pretty sure I have the identical problem. I'm still not sure about a solution though:

>Hi Dave-
>
>Yes you are correct. In my case the bottom of the pre-chamber
>(angled part) was hitting the bottom of the bore before sealing
>around the top of the lip/head surface. I was convinced that
>the mating surface of the head around the upper "lip" of the
>pre-chamber was corrupt. The manual even mentions a special
>tool for resurfacing that area of the head. A phone call to
>"Metrics Motors" (not Matrix) enlightened me as to what was
>actually happening. They said most of the heads for the 603
>are coming that way (they always replace the head on the 603
>engines when rebuilding). They blamed it on sloppy machining.
>
>
>The MB shims for under the pre-chamber "lip" were special order
>and very expensive (for what they were). If the head was never
>planed, you probably don't need them.
>
>Good luck.
>
>Dale

I wonder if this is related to "RunningTooHot's" comments about sloppy machining on the new OM603 heads...?

gsxr · #7 03-12-2002, 04:01 PM

Here's the latest. I pulled 2 prechambers and measure the bore. The new head has a shallower bore than the old head. The p/c hits the angled part before the top sealing lip seats.

The correct fix is to bore out the recess in the cylinder head. I'm not removing the head (again) on my car, so that's not an option. Using the spacer (seal ring) would pull the p/c up too far, it is supposed to be within a 0.5mm range of protrusion from the head. The spacers are available in 0.3, 0.6, and 1.0mm thicknesses. They are designed for use when the p/c sealing lip is resurfaced, to correct the alignment (remove 0.3mm of material, insert 0.3mm spacer.)

What I'm going to try is what Dale did - grind down the p/c body where the radius begins. It should only require about 0.5mm of material removed. The total difference is definitely less than 1mm. It's impossible to measure with the head in the car, unfortunately.

Metric Motors confirmed that the new OM603 heads vary widely in accuracy. Some have this problem, some don't. You need to measure BEFORE installing the head! (Ooops.) TheBenzBin claims you need to install new prechambers but that will NOT cure it, the new p/c are the same physical size and if you're lucky to have a "bad" new head (like me), new p/c's will have the same problem!

Regards,

mbdoc · #8 03-12-2002, 06:03 PM

WE started seeing this problem about 2.5 years ago! MB says to use the later pre-chambers from the OM603.971 engine but you also need the newer injectors & pre-chamber lock rings(all of that costs almost $1000). AT our dealer we have the "NEW" head modified(machine shop) so that the old style prechamber will fit.

Billybob · #9 03-12-2002, 08:23 PM

As my SDL is starting to exhibit some of these freaky symptoms I’m starting to strategize my plan.

Where did you get your "new?" head from and what kind of price? Was it "bare" is so how "Bare" is "Bare"? Did you look for a rebuilt or used head? Would a head off a newer (90's) head swap out I figure if there are so many motors with sloppy cylinders there may be a head available somewhere. Anyone have the list of MB Par t# for these revised heads?

Plus what size is the triple square wrench you need for the head bolts 8? 10? 12? MM Thanks for any info and opinions.

gsxr · #10 03-12-2002, 08:39 PM

Billybob,

1- I got my head it's a new OE Mercedes head.

2- "Bare" is the head casting, with freeze plugs installed, exhaust studs, and valve guides. There are no valves, springs, or lifters included. You can probably re-use your valves & springs. You may want to put in new lifters now, even though they're pricey (~$20 each). They usually only last about 200-250kmi or so and it's a pain to replace them later.

3- There are no rebuilt OM603 heads (that I know of). You can either re-use yours if it's not cracked, or you need a new head. Welding may be an option but it's a gamble as to how long the repair will last.

4- Yes, a newer (90's) head from the 603.97x will swap. Actually, that is the "updated" head for your 603.961! There were 4 different head p/n's total, and 6 different head gasket p/n's!

5- The latest revision head is part number 603-010-96-20. You will also need two longer M8 bolts for the timing chain area, (M8 x 50 instead of M8 x 30), p/n 000912-008062. Re-use the old washers on the new bolts (some modification required).

6- The triple square is either a 10mm or 12mm, I can't remember which. I bought the MB tool, part number 601-589-00-10-00. It was about $20 but I think it was worth it, it's a nice Hazet piece, made in Germany.

7- It is possible that you may need new prechambers too. I'm still trying to figure out that issue on mine. I'll let y'all know what happens!

Regards,

Billybob · #11 03-12-2002, 10:15 PM

Thanks for the info, I'm anticipating the worst so maybe I'll be surprised and lucky! I'm got to buy that triple square and then I'm going to pull the head and look. What’s your opinion as to the new gasket, it appears Elring is the only one available from Fastlane and the others, maybe MB is the best bet? As to the needed bolts, I'll assume that is because the head is now thicker in that area?

As to your prechamber problem? Am I correct in understanding that the recesses milled into the new head are not shaped to fit the older prechambers so the obvious choice is install the new style prechambers, locking rings and new style injectors ($$$) or mill out the head recesses to fit either the old style prechambers (but taking away material will cause the prechambers to seat too deep in the head maybe into the combustion chamber?) or milling to take old prechambers + requisite spacers to obtain proper depth in head and combustion chamber and completely seal where your problem leak is now?

Looking at my 603 Manual you "refinish" the prechamber sealing surface with MB 601 589 00 66 00 Countersinking Tool and then adjust with the .3, .6, or 1. MM spacers?

gsxr · #12 03-13-2002, 01:23 AM

MB Doc,

Thanks, that confirms what I heard from Metric Motors, that the p/c bore on the new heads is shallower than the original heads. However, I have talked to a couple of folks now that just purchased new OM603.96 prechambers for their heads (on OM603.96 engines, obviously), and said that cured the problem. Do you have any TSB or other documentation with more info on the 603.97x parts being the "recommended" fix by Mercedes? My local dealer had NEVER heard of this problem, let alone any type of solution...!

Thanks again,

RunningTooHot · #13 03-13-2002, 03:22 AM

Quote:

I wonder if this is related to "RunningTooHot's" comments about sloppy machining on the new OM603 heads...?

Yep. But you found the right person to talk to. Ask for Mike at Metric - he is a great guy & will help you out. I would definitely ask him about taking material off the PC's vs. machining the head. (It seems a bit risky to me - depending on the original material thickness & stress level at that area).

If Mike says that you need to machine it properly, then I would ABSOLUTELY listen to his advice. You may not want to pull the head again right now, but you may kick yourself in the ass if something happens later. Do it right, do it once.

Good Luck!
RTH

jobah · #14 03-13-2002, 04:37 PM

My understanding of your problem is that the piston is hitting the prechamber. The solution is to purchase shims that are placed proximate the shoulder of the prechamber prior to insertion. Mercedes sells these shims but it is very difficult to find someone with knowledge as to their existence. My buddy did this with his 602 after machining.

Billybob · #15 03-13-2002, 06:13 PM

I believe that it is the failure of the used prechambers and related parts to effectvely seal in the milled recesses of the new head that is the actual problem causing the lack of compression described due to leaking in the first post.

At issue is correcting that failure to properly seal while at the same time ensuring the proper clearences both below (into the combustion chamber) and above (extension of the prechamber and its' sealing ring above the head recess surface)

Apparently the machine work on the new casting is different (worse?) than that of the original casting leading to compatability issues with the original parts. I'm following this issue as I anticipate a possible head replacement in the future.

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