M104.992 / 95E320 Timing Cover Seal Replacement Steps and Pics - PeachParts Mercedes-Benz Forum

EricSilver · #1 03-20-2011, 05:11 PM

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.