Folks years ago somebody here posted a link to the site that deals with the
problems of the 1991 through 1994 Mercedes Diesel engines (M603,M602).
Just last week I rebuild the cylinder head of a 1992 300D Turbo Diesel, which
was smoking pitch black clouds upon start up.
Ended up being a valve guide that was completely lose, going up and down with
the valve, allowing oil to drain into one of the cylinders.
So I figured this week was time to do my own diesel, 1993 300SD, blue smoke in
the morning only for the first 20 feet of driving, than clears up almost
The cylinder head is off as of last night, no obvious problem with the guides,
no obvious cylinder ...1 ,2 , and 3 have more carbon built up on the pistons.
I'm pretty sure that between changing the valve guides, seals, and the new head
gasket that the smoke will go away..but better safe than sorry.
I know there is the issue with bent connection rods, however this engine ran
pretty smooth otherwise, the blue smoke in the morning is pretty much the only
230K on the engine, please anybody, forward the link to the web site that deals
with the issues on these Diesels (1993 M603) I wanna make sure that I don't
miss anything while I'm fixing my own car :-).
That would be nice, but no such luck, their both the same engines.
I don't know why the 92' and 93's were called 300 instead of 350SD's, I think
it had to do with marketing, since the old 126's 300SD's had a very robust
Thanks for your prompt reply anyway, It's almost silly that I post in the first
place since I make my living operating a very successful Mercedes service and
But honestly, we have not come across any bent rod M603's and since I pulled
the head on mine tonight and didn't see any obvious internal leaks I'm sort
Tomorrow I'm gonna clean the valve seals to see if they were dry rodded or
cracked, if they are than that would be sufficiant enough to cause oil to leak
into a cylinder or two.
The head gaskets are also famous for that, and this gasket was socked pretty
good near # 1 cylinder, but then the only question remains why it would only
smoke within a mile or two in the mornings.
I will keep "alt.auto.mercedes" posted on the outcome, it will be about a week
before the car is back on the road again, among the cylinder head I will also
install new motor mounts, flex pipe, brakes all around.
Regardless of play, the valve guides are gonna be replaced with the first
oversize just to be safe.
I am not a Mecedes mechanic, but I am a diesel mechanic and I find this
thread interesting. On the '92 300 diesel you repaired-- the black
smoke upon startup sounds more like a sticking turbo than the loose
valve guide you found. On your engine: You are burning oil. I realize
that pulling the engine, dropping the pan and popping out the pistons is
10 times more work than just R&Ring the head, but that is what you need
to do if you want to do it right the first time. Inspect the rods and
pistons, and if they are good and the cylinders aren't too worn, just
hone it out and put new rings on the old pistons. If you don't want to
do this you can check for a bent rod by checking the piston travel at
the top of the stroke. Also, I wouldn't force oversize valve guides
into the head without mic-ing out the holes and putting the correct size
in. I just did the head on my '84 300D TD and only the intake valve
guides were shot, so I replaced them with std. size guides and left the
exhaust guides alone. I also re-ringed the old pistons and honed out
the clyinders. Runs great and no smoke. This was done at 264,000
General Diesel Service, CA
Your 1984 is a 617 engine, cast iron cylinder head, these 603, 602, and 601
diesel engines from Mercedes have aluminum heads of which the later generation
(1991 through 1995) love to create lose guides.
The 1992 300D I did for a customer last week had this very repair done 5 years
ago, I know because the shop that did it came to me for advice, so they
replaced only the guides that were lose than, and volar 5 years later ended up
in my shop.
So when I pulled those guides (all of them) I found three different materials
used, some guides were cupper, some metal with cross marks, some metal with no
marks (originals) and some were brass.
That's how know that they only fixed the lose ones.
I replaced them all with the next oversize (the only way the dealer will sell
them for these engines) original size's are only available aftermarket.
And by the way, this morning I punched out two of my valve guides, one intake
and one exhaust just to see how tight they were, I was able to punch the intake
out with 3 easy hits, the exhaust 2 hits, so there you have it, they would have
pupped lose eventually.
Yes 617 engines...piece of cake did one 3 years ago, metal fatigue one guide
worn completly causing the exhaust valve not to seal during warm up, I replaced
one guide, one valve, all the valve seals, and even today the runs runs great
and didn't have a re-accurence.
P.S I called the dealer this morning with the engine number, yes my engines is
listed as the trouble maker and should have all the rods replaced, checked with
another source in germany...dito same answer.
Folks, Totally forgot to update everyone.
The valve guide replacement was a total success, although it took a little
driving over the weekend but make sure the head was broken in again.
This morning I only had a slight fog of greyish smoke, but no oil burning on
P.S, Injectors are next, motor mounts and flex pipe are ready to be installed.
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