Cam cover leak repair
 

Been oozing life for 5 years even though I change the gasket to new for every valve adjustment. Since I am feeling flush at this time, I sprang for a factory MB gasket ($21.50 at AhAz).

First thing I noticed was that it seemed heavier in weight than the aftermarket gaskets. Second thing was how tightly it fit onto the cover. In past, I used assembly grease to hold the gasket in place while working it onto the head. No need to this time. After start-up and a test run, I think the typical left rear corner leak is gone.

In this case boys, buy the real thing is my advice.

Whoops; 1983 300CD w/OM617.

Hey Rocky -
I'm doing well with an aftermarket gasket but I flattened the bottom of my cam cover first. It was NOT flat. I fixed it with straight line sander paper stuck to my table saw table and significant elbow grease. The Mercedes gasket may be thick enough to compensate for greater un-flatness (is that a word?) than the aftermarket ones. Oh - and don't over-tighten the hold downs.

Dan

Roger that Dan. Torque spec for cam cover nuts is 10 lb/ft.

Rocky, you don't have enough mileage on the gasket if you've recently changed it. I recently had used a piece of glass and feeler gauge to make sure that the gasket was on the cover correctly. I though it was fine but leaked after a few months. (The glass came out of an old refrigerator and has supporting structures under it. It was free and is more stable than plain glass.)

My latest attempt implemented last week was to go back to gluing it down. I cleaned the surface of the head with a rag sprayed with carb cleaner, applied a very little grey RTV using my gloved finger to the head, let it sit, then installed the cover. The cover was not tight, only snugged. Later I torqued. So far, no leak and it's completely dry - but it's only been a week.

Some people reported filing the bottoms of the bolt holes where the aluminum bottoms out so they can snug the cover down more. I might try that, plus sand the bottom on plate-glass w/ glued sandpaper. Seems the cover in my 1984 is always leaking. It is nasty underneath, compared to my 1985 which stays clean, but there is the benefit of no worries of corrosion under the car.

If the gasket still seems like it has life to me when cover is off I just reuse it and put silicone sealant on it seems to work best as always seems to leak after putting aftermarket gaskets that I get for about 5$ on it. I'll keep it in mind that the factory one works better at 4 times the cost. You would think there is no way they should leak but I guess it is the nature of the animal just like the valve cover oil filler caps leak 1 member made his own up that will never leak I might do the same current one is not leaking.

If I had to guess I'd say that there are 2 root causes of this:

1) The cam cover in question isn't flat and

2) There is really an insufficient number of hold-down fasteners. There are the same number (4 for those not in the know)) as the 616 has and that uses a 20% shorter cam cover. I suspect that the 4 on a 616 are marginal and on the 617 are really not enough. When I build my back-up engine I'll puzzle out a way to add more fasteners and see if that helps (maybe it won't matter but I can't know 'till I try it).

Dan

As was alluded to earlier... If you look at the places where the studs go through the holes on the inside of the cover, those flat spots hit a shoulder on the studs to prevent you from tightening the cover down too much (I assume). The problem is that people really crank the nuts down and over time it deforms those flat spots until the cover can no longer move down far enough to seal against the gasket. Flattening them out with a file a very tiny amount makes all the difference.

BTW, I don't think the gasket sealing edge of the cover is supposed to be flat, but that's just an opinion. I think it's supposed to have a slight curve so that it lays flat as you tighten it down and stays under tension. Regardless, flattening the whole bottom may only cause more leaks as you're creating even more of a space between the cover, which is essentially suspended in the air on the studs, and the gasket.

-Rog

It's worked well for me to flatten mine but I've been careful not to overtighten it. Mine was NOT evenly curved in some manner that could have applied additional clamping force - it was high and low here and there around it's perimeter with no particular pattern. I started with it on the table saw top and used feeler gages to look for gaps, which there were as described above.

Dan

I guess I am of the opinion that the Mercedes designers are at least as smart as I am. I have made a lot of changes to my 300CD but probably no improvements. I have functionally changed some features and eliminated others.

For basic assembly form and fit however I don't think I can improve on their design. As Junkman suggests, I think that I am not quite finished. A drive to work tomorrow getting it up to temperature and keeping it there for a while will tell the tale. I will recheck torque tomorrow evening. The way the OE gasket went on though gives me great confidence that it will be fine.

I really didn't expect this post to grow legs so I will report back tomorrow evening.

I put my cover on the glass shelf taken from a refrigerator. There was not enough space to see through or obvious space and the thinnest feeler gauge did not go between the shelf and cover.

Filing the cover whether is is the entire surface or only the bottom of the bolt holes reduces clamping force of the nuts. I did make sure that the shoulders on the studs are clear and that the cover can fully seat on the shoulders.

I also used a straight edge on the bottom of the gasket when the gasket was mounted on the cover. The gasket can be put on so that it is relatively flat as measured by the straight edge. It will also stay on the cover when mounted correctly and not pull off the corners of the cover.

A little RTV (very little) put on the head (Not the cover) seems to work. More miles will tell.

This thread was helpful in cleaning up the engine.

http://www.peachparts.com/shopforum/diesel-discussion/328295-leak-free-617-a.html

Once you understand how the fitment works, you'll know that shaving anything off of the bottom of the gasket sealing surface does indeed reduce clamping force in regards to the gasket, but removing material from the bottom of the stud holes increases clamping force. You're tightening the cover down onto the shoulders of the studs, not onto the sealing surface on the head.

I made an incredibly crude diagram to illustrate this, since it seems a lot of people have trouble visualizing it:

https://lh3.googleusercontent.com/FA...M=w800-h600-no


The two red spots are the only contact areas that matter in regards to how tight the nuts are. That's why tightening the nuts more doesn't close the gap between the gasket and either the head or the cover more. It does, however, deform those contact points on the cover, which can actually increase the distance between the contact points and the shoulder on the studs and thus the distance between the cover and gasket.

Shaving material off the red areas makes it so the cover moves closer to the gasket.

I completely agree with the statements that there are too few nuts holding the cover down. I think that and over-tightening are why there's such a big variation in warpage when people put them on a flat surface. Maybe they're supposed to be flat, maybe slightly curved...it's hard to say since so many seem to be twisted. But I think the reason they have only four nuts is that they thought their plan of suspending the cover above the sealing surface was going to be foolproof. Little did they know that it would be not obvious how the cover is sealed so people would think that cranking the nuts down would clamp it down more. Kind of the opposite is true.

Also, the wave washers are important because they seem to take up any slack that happens as the metal expands and contracts with heat. This is another avenue for leaks.

-Rog

If it works as in pic above, why the low torque number for hold downs?

Specifically because that's how it works. You're only snugging it down onto the studs. Once it bottoms out on the studs there's no farther it can go, regardless of torque. So more torque would be not only pointless but would damage the contact points on the cover.

-Rog

By the way, anyone would totally get it if they just installed the cover without the gasket. You'll see it just floating there above the surface of the head. Then install the nuts and see that it's still just floating there above the head.

-Rog