This weekend I'm going to do another DIY writeup (like the ball joints http://www.peachparts.com/Wikka/W124BallJoint ) for replacing the gasket on the top timing cover at front, aka the u gasket. I've done this before and used Hylomar and had good results but I know there is a bit of debate on which sealant to use. Before I do the DIY write-up (and the repair) I'd like to poll everybody for their recommendation.

Thanks!
Robert

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89 300te 222,222
92 300e 190,000

Well as you may already know, I gave in and bought the oem stuff since that was the only one available in my area, and I didn't want to have to order by mail. Feel free to look at my thread:

M103 Oil leak or burning?

Make sure you look at:
Post #51 on Page 4 and also Page 5

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

Robert:

Forget the sealant. It's like the oil/coolant debate. There are several sealers that work on the U-Gasket. The process that you're about to prepare is what counts.

Thanks for taking the time.

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'91 300-SEL

I used the black OEM stuff from the dealer and it has held up fine for several months now - I think proper preparation i.e. cleaning of the mating surfaces is the most critical step. If the mating surfaces are 110 percent oil-free and you torque properly, you could probably use bubble gum and it would hold.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Don't take the sealant choice lightly. This is a very specific application for sealant. The key is that the sealant has to be slimey slick so that you can slide the cover rearward without displacing the seal, but it has to have some body to it so that it will goop up in the corners.

I'm sure that there are other sealants that will work, but you would have to experiment to find it.

When starting the shaft seal over the camshaft, use your fingernail to ensure that the seal does not "fold" and slips over the shaft properly. Put a light coat of oil on the sealing surface of the camshaft before doing this.

Good luck,

I did this job earlier this week.

I used a sealant from FastLane called, I believe, Curil. It was in a tube with German writing all over. It was black and looked and smelled exactly like some old Permatex gasket stuff I've used in the past.

Oh, and no leaks.

And, I installed the new camshaft seal AFTER the cover was in place. Seemed safer to do it that way.

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2012 E350
2006 Callaway SC560

I just completed a valve/timing chain redo on my 1992 300SE and after ScotchBriting all gasket surfaces and liberal use of contact cleaner, I installed the lower cover without the crank seal and used Permatex Ultra Grey gasket maker for about $6.00. I set the U-shaped seal in place using the permatex. When it had set (24 hours) I cleaned it up with a razor blade and then installed the top cover using the Permatex. It has been 4k miles and it is dry as a bone. I think allowing the 24 hour setup prevented the U-seal from slipping out of place. As far as having to use the MB sealers, the cost is much greater. To me, metal is metal, rubber is rubber and if the Permatex works on Fords and Chevys when applied properly then it will work on MBs if applied properly also. Time will tell.

Tim

Thanks all for the tips in advance. I will be sure to demonstrate good cleaning of the surfaces prior to applying sealant. How does lacquer thinner or acetone sound?

Given the lack of concensus on which sealant to use I think I'm going to stick with the Hylomar. It seems to have the goop factor that Larry mentions, and I've used it with success before.

I should have the DIY posted on Monday.

Thanks!

Robert

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89 300te 222,222
92 300e 190,000

I used brake cleaner in a spray can.

Regarding the sealer, someone before me had used a black sealer that was BRITTLE and broke right off. There were also a few squirts of clear RTV scattered about. I think the key is to use something that remains pliable.

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2012 E350
2006 Callaway SC560

I just did this job last week. On the recommendation of one of the members I tried Threebond 1211 with excellent results. Absolutely no more leaks.
Colin

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92 Mercedes 300E 2.6
86 Plymouth Conquest TSi
79 Chrysler Cordoba (without Corinthian Leather!)

DRIVE FAST TAKE CHANCES!

Absolutely the only sealant to use for this application is Loctite 5900. It will last for YEARS not months, all this other stuff will be leaking again in a year.

For cleanup I use a combination of scotchbrite pads and brake cleaner. Sometimes a single edge razor blade and a small pick will be helpful.

The seal in question is universally called the "lip seal". The cover you are removing to replace the lip seal is called the cylinder head front cover. The leak typically is between the front cover and the head, the lip seal itself isn't a problem, the gap is set by the bolt positions and isn't changeable, of course it can leak at one of the ends of the lip seal if not enough sealant is used. The cam seal Larry referred to is called the radial seal, it should be replaced every time, and helps to have the correct installation tool.

The sealant should NOT be put on the surface of the lip seal, just back in the corner of each groove the lip seal lays in to. I recommend a light smear of oil on top of the lip seal and the perimter of the radial seal to help slide the front cover back in to position.

Be sure to torque the 4 bolts that hold the front cover in place, then reassemble the rest of the engine, and for a DIY job I'd let the engine sit overnight to allow the sealant to cure, without starting the engine.

Gilly

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Interesting tip on the 5900. I pulled the tech specs on that and it's RTV silicone with "heavy body". It's specially formulated to retain flexibility after curing.

From reading the spec sheets of a few RTVs and Hylomar they all seem like total overkill for the application, maintaining flexibility and stability over months at 500 deg f, and several hundred PSI and oil/fuel/coolant.

I wonder if there's anybody out there who has done a diligent job cleaning up the mating surfaces and had a leak within two years. Anybody have a leak to mention that was caused by the sealant?

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89 300te 222,222
92 300e 190,000

It's ALWAYS the sealant, and yes when MB was trying to figure out what sealant to use, we got comebacks on lip seal jobs ALL the time. Well, OK, eventually the lip seal will get hard and maybe leak, but will last as long as a valve cover gasket for example, 5 + years. 5900 is what MB recommends for this job, those of you with access to WIS can research this, there is an SI that was put out in regards to it, find it in the same group you find work instructions for replacing the front cover, the info may also appear in the work instructions by now, or there is a link to it in the work instructions. The main place it's used is on the sealing face between the front cover and the head, no reason to "pile" it on there, about a 1/8" bead is enough, certainly less than 1/4" bead. The only other spot is about 1/4" ball of it at the very ends of the groove on top of the timing cover, in the ends of the small channel the lip seal fits in to. As I said it's a great benefit to have the installation tool that slips in to the camshaft, really helps line everything up when slipping the cover back on. There are TWO different sized tools, I believe the bore in the front of the camshaft changed sizes some point early in production. If you borrow the tool and it won't go in to the camshaft or is way too loose, you need the OTHER one. Just a light film of motor oil (synth or dino ) will help the cover glide back in to position, you do need a slight amount of downward push to get it to go back in to place, if you can't get it perfectly flat in back, don't worry the bolts will finish the job, but by ALL MEANS check the gap between the front cover and timing cover (the lower, main timing case cover) to make damm sure the lip seal didn't "roll" or come out of place! Then go ahead and torque the 4 bolts and you want, as a DIY'er, for this stuff to cure as long as practical, overnight would be a good thing. Don't start the engine during this time, you don't want oil to get on this stuff, that's why I mentioned a THIN film of oil on the new lip seal, just enough to make it slick. Be sure to clean all the old junk off the front cover, including where the lip seal contacts it, and especially where it contacts the head, and of couse the tough part is getting the old junk off the front of the head, drivers side is a bit harder than the passengers side, due to the tensioner shock, etc being in the way. I use a tiny screwdriver to pick away at the old junk around the 2 steel dowels, also clean off the tops of these dowels and clear the dowel holes they fit in to. Clean the old junk out of the groove the lip seal fits in to. If you look at the ends of this groove, you'll see the small gap between the head and engine block, it'll be kind of obvious that this is what the small ball of 5900 is supposed to seal up. Still, don't overdo it, this isn't a case of more=better. But realize what you are trying to do.

Gilly

PS Many times you will see the old junk is a creamy white, sometimes turns yellowish to light brown, that was recommended for a few years, see that quite a bit, sometimes a greenish stuff was used, lasted a short while. You may also see the typical blue or red RTV's used, these don't last long either, usually by shops or DIY'ers that never really researched what should be used.

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Gilly - excellent write-up. Thanks for the diligence. This will definately make it into the final DIY write-up.

On the rubber lip-seal, what do you think of using hylomar instead of oil? I know it might be overkill, but would it be deleterious?

Robert

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89 300te 222,222
92 300e 190,000

Ive done this job on my car recently & the only issue I had was it was hard to put the upper front cover on with the cam seal already installed.It seemed much easier to put the cover on then carefully put the seal on.This way I didnt disturb the u-gasket at all.I didnt even have to lube the u-seal since the cover set on top of the gasket instead of dragging the upper cover over it.I used the factory sealant.