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Old 12-28-2006, 09:11 PM
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Join Date: Nov 2006
Posts: 6
An Idiot w/a Chain Cover Seal on M103

Well boys, I'm goin' a bit crazy. Pick up my new to me 92' 300E two weeks ago and it came with the classic top chain cover leak. Thought to myself, no sweat, I can fix that.

First attempt was made following instructions to the letter. Still had the leak.

Second attempt was made using Mercedes sealant (loctite 5900) and instructions from the shop foreman at the local Merc dealership. Still have the leak.

I'm losing my sense of ha ha over this one.

I've gone over the proccess in my head a dozen times and can't think of what I've done incorrectly. Old sealant was removed, mating surfaces oil free and sqeaky clean (solvent and denatured alchohol), dab of sealant in the corners, horseshoe gasket properly seated with a drop of oil on the top surface, thin layer of sealant on the back of the cover, new radial seal for the camshaft......

Feeling like a spaz and I'm stumped!

Any old pros out there with the secret trick.

The chain cover is dry all the way around except for seepage (3 of 4 drops overnight) at the bottom passenger side corner. Could I have a head gasket leak at the front passenger corner? Is this a common issue on the M103?

The dealer's service guide states, "that if resealing the chain cover doesn't eliminate the leak... head gasket needs to be replaced"

Tell me it ain't so.

The car has a legitimate 56,000 miles and is, othewise, in immaculate shape. I could live without pulling the head. Any thoughts??

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Old 12-29-2006, 12:01 AM
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Location: Northern Va.
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That would drive me crazy too. I did the same service on my 300SE a few years ago and it's been good since then. If it's 3 or 4 drops, you might just leave it and check the oil regularly.

You might check the oil level O-ring for leaks. It's on the driver side of the oil pan front sump.


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Old 12-29-2006, 12:49 AM
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Join Date: May 1999
Location: Sacramento, CA
Posts: 1,565
I'm about to repeat this repair on my 300E, although mine went a couple of years before starting to leak again.

Did you let the sealant sit/cure overnight before starting the car?
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Old 12-29-2006, 01:10 AM
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Join Date: Nov 2006
Posts: 6
Originally Posted by anthonyb View Post
I'm about to repeat this repair on my 300E, although mine went a couple of years before starting to leak again.

Did you let the sealant sit/cure overnight before starting the car?

You may be on to something.

The black all purpose sealant supplied by the dealer comes with precious few directions. States that you shouldn't eat it and that it sets up in 20 minutes. I assumed that meant you could put the vehicle back in service in under a half hour. Guess I was wrong.

Does anyone know the curing time for the Merc supplied sealant?

The suspense was killing me the second time around and I ran the engine after an hour to leak test it.

Thanks for the tip.
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Old 12-29-2006, 04:50 AM
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Location: San Francisco, CA
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I let mine sit for a few hours ..... AND I replaced the valve cover seal. Additonally I made sure the area around the bolt holes were flat and not crowned and that I didn't over-tighten the bolts.

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Old 01-01-2007, 12:32 PM
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Join Date: Jan 2003
Location: Dallas
Posts: 792
Ah, yes, the dreaded seepage of oil just behind the evil cover on the passenger side. Kinda runs down toward the chain adjuster plug - and if it gets bad enough, it runs all the way along the underside of the head and down the right rear of the engine.
It sure looked like a head gasket to me, but it was indeed the cover seal.
Seems to last about 5 years, and starts seeping again.
actually, mine is seeping a bit right now, so here we go again (4th time).
- Sounds like you cleaned everything really well - I use a sharp pick to get every little spec out of the groove where the seal butts up to the head.
- There is one bolt, lower driver side, that screws into a threaded hole that is open to the oil passage. This bolt should have a dab of sealer on the threads.
- I found the best lubricant for the seal to slide the cover over is "spit".
just spit on it, slide the cover on; the saliva then dries quickly and the rubber sticks well to the metal cover. As directed in the manual, I only use sealant on the ends of the seal (and of course on the metal mating surfaces of the cover and head.
- if the radial seal is leaking, you should be able to see traces of oil under the rotor cap, so that should be easy to rule out.

Good luck,
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Old 06-01-2007, 11:02 PM
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Join Date: Apr 2001
Location: Joliet Illinois
Posts: 309
Successful Reseal

I agree with the Guru.

The key is to a successful reseal is to really clean the corners where the cover meets the head gasket. That is a point that is prone to leaking. There is a crevice that you need to use a pick to clean out until you see the metal edge of the head gasket. Old sealant in the crevice will cause problems. Also use a non-oily solvent, like alcohol, to clean the surfaces before sealing.
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Old 06-02-2007, 11:49 AM
Join Date: Apr 2007
Posts: 13
Oil leak

I noticed from your enclosed pictures, you have not removed the rocker cover, this must have been a struggle for you to refit the timing cover.

That struggle in its self, could have caused the seal to dis-lodge, causing your presistant leak. As long as you smear a bead of sealant at the two corner edges of the head/timing covers and also some sealant seamered to the bottom left t/cover screw. You should have no problems. Check for squareness of the t/cover mating edges. Do not put sealant on the t/cover seal, just the corners is adequate. Smear a small amount of grease on the seal to allow the t/cover to slide onto the seal whilst fitting, without being dislodged. Good luck.

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