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Old 03-20-2011, 05:11 PM
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M104.992 / 95E320 Timing Cover Seal Replacement Steps and Pics

M104.992 / 95E320 Timing Cover Seal Replacement Steps and Pics

This is what I did. Pictures with captions at the end.


ONE: Remove Fan Shroud and Coolant Pipes
Remove Fan Shroud
Remove Front Cover
Disconnect rubber coolant hose (screwdriver or 6mm socket for pipe clamps)
Remove heater crossover pipe (10mm bolt)

TWO: Remove Switchover Valve and Engine Hook
Remove Switchover Valve (two 10mm bolts).
Mark removed SOV electrical & vacuum connections with numbered tape for easy reassembly.
Undo Air pump electrical connection and mark with numbered tape.
Unbolt camshaft position sensor.
Remove engine lift hook (two long 5mm Allen head bolts) next to the switchover valve

THREE: Remove Fan
Undo the three 5mm allen-head bolts that secure it to the clutch. Hold fan hub by hand to keep it from spinning when you loosen bolts.

FOUR: Remove Valve Cover
Remove air cleaner cover and crossover pipe.
Remove Sparkplug cover
Remove ignition coils and wires. Mark with numbered tape for easy reassembly.
Remove wire harness where it attaches to valve cover. You will need to unbolt two connectors which will be obvious when you see them. One, in front, uses a 10mm bolt. The one in the rear uses a nut of the same size as coolant expansion tank mounting nuts.
Unbolt and Remove Valve cover – on the left/passenger side of 104.992 engines there is a metal vacuum line that attaches to two valve cover bolts and runs from the EGR “saucer” to the SOV.
Cover valve train with plastic and then a towel

NOTE: Don’t lose the two half-moon gasket pieces that sit in the back of the head.

FIVE: Remove Timing Cover
Remove six 13mm bolts. The lower-left (passenger) bolt will not retract completely because the Top Guide/Idler Pulley is in the way. But that will not interfere with cover removal. Just make sure you do not lose the bolt when it slides out after the cover is off.
NOTE: There are 3 long bolt bolts and 3 short bolts. The long bolts are Top Left (passenger), Top Right and Middle Right.

Midway down the right side of the cover is a gap that you can insert a strong screwdriver into to gently pry it apart. That will open a gap on the top passenger side, where you can then also gently pry from. Cover will slide off – along with upper plastic chain rail (m104.992 engines).

NOTE: It is immediately obvious why these covers leak in the specific location they do: 1)The engine slopes from right to left; 2) The left side of the cover is wider than the right, making it easier for oil to pool; 3) There is a substantial gap between the block and head on the left – and once it opens you get a sizable leak.

Had MB engineers caught themselves they could have cut a v-shaped notch on the left (passenger) side of the head to drain oil from that area to prevent pooling, and probably eliminate the need for these reseals. I earnestly believe oil pooling is the issue since the front and right sides were bone dry.


NOTE 2: The old seal will be in Perfect condition. You could probably reuse it if you wanted.

SIX: Clean Mating Surfaces
Clean the mating surfaces of the timing cover and head, and the groove the seal sits in.

SEVEN: Insert New Seal and Reassemble
If you have a 104.992 engine, and you are NOT removing the chain tensioner, you will not be able to reinstall the cover without rolling the seal. This is because the upper chain rail, when finagled back onto the cover and under the chain, puts strong downward force on the cover, which makes it impossible to slide the cover straight over the seal. You might try to "walk" it on -- left corner forward, right corner forward, and so on in little steps, but you will still roll it in the middle.

Unless the seal is immobilized, you will not get the cover aligned properly, nor the top chain guide in place, now matter how hard you try. Note: You will be especially frustrated if you try putting plastic over the seal to keep it from rolling. All that will do is create a larger friction footprint and roll the seal more easily. That method only works for folks who let the chain go slack.

What follows is my workaround, some aspects of which may be controversial.

1. Using sharp scissors and/or a razor blade, carefully shave the front part of the seal into a 30-45 degree bevel.
2. Put a very thin coat of Gorilla Glue on the bottom of the seal and press into channel. Let it cure overnight. Seal will be secured into place and immobilized.
3. Spread a thin film of oil or other lubricant top of the seal.
4. Dab sealant on ends of seal. Loctite 5970 is universally recommended. I, nonetheless, used Permatex Copper for its strength, flexibility, oil resistance and high heat tolerance.
5.) Position the cover in line with the guide pin(s) and bolt holes; and the upper chain rail. The latter is tricky since the top of the cover needs to be slid back and tilted back while the bottom is still sitting on the seals in order to get the two posts on the top of the cover into the appropriate holes on the chain guide while holding the guide, by hand, under the chain. This is much, much easier if you immobilize the seal.
6.) Begin inserting and tightening the bolts, bearing in mind that three are long and three are short. As you are tightening the bolts, stop frequently to shine a flashlight into cover compartment to make sure the seal is not being displaced. There should be a thin sliver of silver metal visible from end to end at the back of the seal. When the cover is fully secured there should be an uninterrupted green line at the front of the cover.

Note: If you do the bevel and glue technique you will successfully reattach cover on the first attempt, without rolling the seal.


EIGHT: Sealant Curing
Allow a few hours – or overnight -- for sealant to cure. In that time, reinstall the items in steps 1-4 above. Would be a good time to also change spark plugs and replace valve cover seal.

PICTURES

I find it helpful to secure instructions to the car with magnets. A discarded floor mat protects the paint from the toolbox:



Getting started: Front cover off. Switchover Valve on left. Engine Lift Hook dead center:



SOV, Engine Hook, and Fan removed:




Use masking tape to label connectors, and their receptacles, for easy, error-free reassembly.



Also helps to label ignition coils and wires for fast reassembly:




Valve cover off:



Protect valve train with plastic:



A towel keeps plastic from blowing away:



Timing cover off. Alignment (and tensioner??) pin on right chain rail. Note the gap on the left seal channel:



Closeup of gap. There is no solid material from the U-Seal to the left edge; just air. Is it any wonder these engines leak in this spot?



Conversely, the end of the right-side channel hits solid metal No gap:



Cover off. Note upper chain rail at top and the two posts it slides onto:




New seal in place. The front ridge is your enemy. If the seal was flat/solid on top – or if the channel between the two ridges had a metal reinforcement -- it would not roll. If you think you can concurrently align the cover with the guide pin on the right AND slide the cover into the upper chain guide without rolling the seal, think again.



Right side seal with dab of Permatex Copper



Left side seal with bigger dab of Permatex copper.
Sealant to the left if the seal is external and unnecessary but I put it there to more easily identify the leak point from outside:



Mating surfaces of cover with sealant:



Be careful with the top chain guide; I chipped some of the bottom of the lower left hole:



New Seal -- Beveled.
Compare with photo of untouched seal and you will see there was no significant loss of material on the forward/outside edge. (The rear/inside edge is what does the work and is fully intact.) There is a bit of tan-colored dried glue that will flake off on its own when the engine gets hot so I did not clean it off. The seal was completely immobilized and, with a bit of motor oil as a lubricant, the cover slid onto the seal, with a solid green line in front, on the first attempt.

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1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

Last edited by EricSilver; 03-21-2011 at 09:30 AM.
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Old 03-20-2011, 05:28 PM
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Also, I am certain there is a simpler, correct way to install the top chain rail. If someone would be kind enough to post that I (and others) would be grateful.
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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black
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Old 03-21-2011, 12:00 AM
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Thanks for posting this. I thought I read that it is recommended to remove the timing chain tensioner and then re-insert it after the cover is back in place but your method worked.
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Old 03-21-2011, 12:10 AM
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Pics are AWESOME! Thanks so much for contributing. Will help quite a few!
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Old 03-21-2011, 06:26 AM
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Quote:
Originally Posted by vexed View Post
Thanks for posting this. I thought I read that it is recommended to remove the timing chain tensioner and then re-insert it after the cover is back in place but your method worked.
In all of the how-tos I read it was recommended to do that because it allowed the cover to be set down atop the seal rather than slid forward, to avoid rolling the seal. However, that would not have helped me because the closer the cover was to the head the harder it was to get the top guide rail on. (I would, however, now like to study how to use the tensioner in case I ever need to replace the top guide rail.)

The craziest part of this repair is that it was entirely unnecessary.
The old seal was in perfect condition. Only the dab of sealant was gone from the left side gap between the block and head.
This could have been remedied externally, without taking the engine apart.


Look at the photo below where the pick is. That gap will still be there, and just as accessible, with the timing cover in place. If I had to do this job again I would simply clean and degrease that space thoroughly, inject in some sealant with a syringe-type applicator, pack in a bit more on the external juncture of the head and cover, and call it a day.

That is why, in one of the above photos, I used a big gob of sealant on that side. Even if the dab at the end of the U-Seal wears away, oil must still get past the larger mass farther out. Considering how well Permatex Copper sticks to metal, and how impervious it is to oil, that will take some doing.

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black
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Old 03-21-2011, 06:36 AM
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Quote:
Originally Posted by sptt View Post
Pics are AWESOME! Thanks so much for contributing. Will help quite a few!
I hope so. This was the first time I have ever been inside my engine so I was very cautious about doing it and researched the procedure for months -- and still uncovered things that were previously undocumented -- stuff I am sure people encountered but never mentioned.
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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black
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Old 03-21-2011, 11:25 AM
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After my remark about doing this job externally I have been giving it a lot of thought. I would appreciate any good feedback on what I am suggesting below.

Injecting sealant into the leaking timing cover/head gap from outside, and below the timing cover would accomplish precisely the same thing as dismantling the engine to put a dab of sealant on the end of the U-Seal.

I would need a syringe and large-enough metal needle for precision, and to make sure I could get as deep into the gap as possible. A food seasoning/marinating syringe from any housewares store should facilitate that. Squeeze sealant (Permatex Copper or whatever suits you) into the syringe, attach the plunger and you are set.

What I envision is removing the valve cover and inserting the needle through the gap from below/outside until I see the tip emerge near the U-Seal (or feel it bump up against the soft U-Seal). Then pump the syringe and slowly back it out as the sealant fills the gap.

As long as the bonding surfaces are clean and grease-free the sealant will stick. (I have pieces of metal that Permatex Copper absolutely refuses to let go of.)

I think this is a much more sensible way to do this repair.
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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black
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Old 03-21-2011, 01:36 PM
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Eric, if I encounter a leaking upper timing chain cover on a 104 engine I will certainly try your recommended procedure to seal it externally before spending the time/effort of disassembly/reassembly. Great idea!
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Old 03-21-2011, 10:58 PM
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The reason you had a problem with the upper guide is because the you didn't remove the chain tensioner on the pass side of the engine. With the tensioner removed you can roll the cam forward and the slack will allow removal of the upper guide. The left side guide pin is easily removed with one of the bolts you remove from the cover and a small 3/8 drive socket to use as a puller. It really does make the job easier. When I was a tech for MB we used to change these seals and head gaskets daily. Nice write-up.

-Jim
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Old 03-21-2011, 11:41 PM
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Jim, Thanks.

In the photos, I don't see a pass-side guide pin; just the one on the drivers side (right side in photo).

I read descriptions of the process, including the ratcheting of the tensioner after reinstalling it, but it was not clear whether that applied to this specific engine since my layout did not match what I saw and read in the how-to's I relied on, so I did not try it.

Although I chipped the upper guide's post hole a bit it does not appear significant. But, like dirt swept under a rug I know it is there and will likely replace it. Are the steps the same for my engine -- and what, exactly, does it look like?
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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black
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Old 03-22-2011, 02:46 AM
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Could the expert confirm that the same procedure also applies to my engine M104.995? car is 1996 E320 but W210 instead of OP's W124
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Old 03-22-2011, 11:35 AM
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The guide pin is on the left (Driver's side) the right side guide rail floats to take up tension as the timing chain stretches and the rails wear. It does have a guild rail pin similiar to the one on the left it is located at the bottom of the rail in the lower timing chain cover and does not need to be removed for this service. The tensioner is on the right (pass side). Not removing the tensioner when servicing the upper timing chain cover can cause premature failure of the timing chain or guide rails. When you removed the upper guide you run the risk of the tensioner further extending and putting excessive pressure on the chain/rails after reassembly. If your cams never moved you nothing to worry about, but if the exhaust cam rolled back the slack would be taken up in the chain and then when you forced the upper guide back in the chain would be over tightened. There really is no way of knowing if this happened until the guide rail cracks. For the price of the aluminum washer that you have to replace when you remoce the tensioner it's worth doing just to be safe.

-Jim
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90' 300e 2.6 - Silver Donated to a family member
95' C280 - Artic White
88' 924s - Guards Red Sold
98' Durango SLT - Silver
93' 740i Tripple Black Sold
95' 900s Conv - Red
96' XJ6 - Black - For Sale
95' 325i Convertible - Montreal Blue My Project Car

Last edited by Jim_P; 03-22-2011 at 11:55 AM.
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Old 03-22-2011, 11:46 AM
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Quote:
Originally Posted by Texholdem View Post
Could the expert confirm that the same procedure also applies to my engine M104.995? car is 1996 E320 but W210 instead of OP's W124
Pretty much identical. You have the later style belt tensioner, as far as the upper timing cover they are the same. I prefer the MB sealant over permatex as it goes on thinner and has better sealing properties. The sealer for forming a gasket on the cover sides is a yellowish green color. Before installing the U shaped gasket put a line of silicone (permatex if you like) in the corner between the head and the lower timing cover then fit the gasket. The O Ring on the back side of the upper timing cover should get a small dab of sealer to hold it in place during assembly. O rings do not require gasket sealer to form a proper seal and some sealants could react with the rubber and cause it to breakdown over time. We used to use this clear grease that was used on the sunroof tracks to lube any fitting that was sealed with an O ring. It would hold the O ring in place in some instances and aid in assmbly in others.

-Jim
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97' SL600 Sport Pano - Silver
90' 300e 2.6 - Silver Donated to a family member
95' C280 - Artic White
88' 924s - Guards Red Sold
98' Durango SLT - Silver
93' 740i Tripple Black Sold
95' 900s Conv - Red
96' XJ6 - Black - For Sale
95' 325i Convertible - Montreal Blue My Project Car
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Old 03-22-2011, 05:12 PM
Texholdem
 
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Thanks Jim!
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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE
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Old 04-19-2011, 02:44 AM
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I am also having some oil leak in the front cover, and is looking to replace the U-seal. After reading Eric's DIY, I am thinking whether it is worthwhile to try the external method first, namely, filling the leakage point with sealant.

What do you think?
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