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  #1  
Old 07-30-2001, 11:07 PM
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Join Date: Apr 2000
Posts: 460
Valve seals - the aftermath.

I finished replacing my valve seals today, and am I ever glad that job is over! The reason I went ahead with the job is that I was having a little rough idle in the morning with quite a bit of blue smoke, which I figured was tell-tale of bad valve seals. What I want to let everyone think about before they do this job is to first install new injector seals. I did these as part of my valve seal job, and when I pulled the injectors I thought to myself "I bet this is the problem." The injector seals were leaking and when I pulled out the injectors, the barrels they screw into were filled with oil. Now I'm thinking that this is were the oil and rough idle was comming from. I could be wrong, and hopefully all that work replacing the valve seals will be helpful, but if anyone out there has what they think are symptoms of bad valve seals, my advice is to first replace your injector seals.

The other good thing about doing this job is that I found out my timing chain, at 148k, has NO stretch. Was very happy to find that out. If anyone has any questions on this job, feel free to email me.

Greg
'84 300D

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  #2  
Old 07-31-2001, 11:04 PM
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Well, this morning I STILL had the hesitation. What in the world would cause this hesitation, sort of like a hiccup, for about 5-10 seconds in the morning? I think the blue smoke is gone, so the valve seals got rid of that, but I would love to be able to have this thing start as well cold as it does when warm. My old Jetta diesel used to ROAR to life every morning. I hate this hesitation.

Greg
'84 300D
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  #3  
Old 07-31-2001, 11:21 PM
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Join Date: Feb 2001
Location: Midwest, USA
Posts: 171
Thumbs down I think the hesitation is normal...

Hi Greg, I have read over and over again on this forum that the diesel's are slow "in the morning". They really crave that warmed up engine. Mine shifts slowly for about a block. I have that idle adjustment knob, so I can crank up the idle when I start it up, even in the summer, it makes a big difference as far as smoke and idle goes.

I too replaced my valve stem seals, and I was curious about your injector seal replacement. I had great success with the valve stem seals. It was like night and day. My car was smoking so badly when "cold" at the Bank drive thru, and fast food drive thru's that people would back up. I was embarrassed to drive the car anymore. The new seals fixed the problem in a major way. I cannot see smoke anymore at all.

How were your old seals? My exhaust seals were so dried out and loose that I could spin them, and practically wiggle them. I remember that the manual said the intake/exhaust were different, but when I got the seals they were all the same, and I was concerned about it, but Mercedes decided that the small difference wasn't worth making two different styles anymore, so they updated the seals to the same design for both.
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Old 08-01-2001, 01:54 PM
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Join Date: Jan 2001
Location: Mebane, North Carolina
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Well GregS it seems we were on the same wave length. I worked all day yesterday replacing the Valve Seals on my 1981 240D. I rebuilt the engine only 65000 miles ago but it has been using quite a bit of oil since it had about 45000 so I decided to try this fix first. I experienced the same thing you did when I pulled the injectors to gain access to the valves, although I had come to a different conclusion than you did on where the oil came from. I think that when you take off the valve cover. oil around the edges where the gasket seats had ran over the sides and down around the injectors.
Back when I did the rebuild on my engine I had a local machine shop install new valve guides and do a valve job, but after what I found out while doing the valve seal replacement alarms me. I was checking each valve as I went for Wobble of the stem, it seems that all four of the exhaust guides are worn already, but the intake guides are tight. To anyone reading this post, What could have caused the exhaust guides to wear before the intake guides.
The seals I took out of mine did not look like they were that worn so I guess the exhaust guides in mine are the reason it is using oil.

My 1981 240D

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Old 08-01-2001, 05:59 PM
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Well, today was actually a little better. It only hiccuped a couple times and there was no smoke that I could see in the rear view mirror, so things are looking good. On the other hand, I never had the problem Super Turtle did. My car never smoked that bad!

As for your valve seals, I might point the finger at whoever rebuilt your head. Can you trust them? There is a good chance they wobbled the valve and said "good enough," without actually replacing them. I don't think guides wear out except from heavy use. If the valve seals don't fix your oil use problem and you know your compression is good, I bet you could be loosing oil because of those bad guides. I too was checking wobble as I went along, and fortunately I only had a slight wobble in the rearmost intake valve.

Don't really know how old the seals were since I just bought the car about 6 weeks ago. Probably a good chance they were original.

Greg
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  #6  
Old 08-29-2001, 11:57 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
MBJOE:

The usual reason for excess clearance in MB diesel exhaust valve guides is that the shop, not bothering to buy MB parts or read the instructions, put in steel guides and reamed them for a "large" (read Chevy) clearance.

MB (and probably all other diesel engine makers) use sodium filled exhaust valve stems. These get hotter than "normal" exhaust valve stems to transfer the heat from the "head" of the valve to the cylinder head cooling system. Hence the bronze guides MB uses -- they expand faster than the valve stem as they heat up and tranfer heat much better than steel.

Steel valve guides get "stretched" rapidly, and the typcial "american" engine has a rather large clearance between the valve stem and guide. MB diesels will blow enormous amounts of oil into the intake if the exhaust guide is oversized. Lots of oil will leak down the guide when the engine is shut off, too, hence the blue smoke on startup.

New stem seals won't fix this, you need to have the guides replaced (read valve job). I've also seen "cheap" valve rebuilds where the intake valves were replaced, the bronze guides were replaced with steel, and worn-out exhaust valves re-used -- they are expensive ($50 apiece), but such a job will always give trouble.

Another reason to pay the guy who really does good work on MBs -- and if you do your own, you have to know enough not to get screwed by the "machine shop" that does the work -- we have no local ones with metric measuring tools!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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