Oil leak at valve cover studs - PeachParts Mercedes-Benz Forum

Shern · #1 11-01-2021, 09:52 PM

Kind of a strange one...

Under the hood the other day and noticed oil at all four corners of the valve cover.
Seemed to be coming from the valve cover nuts, pooling in the threads and then dripping downward.

I pulled the cover, cleaned everything up and reinstalled.
After a short drive, I can see a bit of wetness on top of each stud.

I always buy the thick MB gaskets and torque to 11ft pounds.
I've never had one leak.

Possible this is a gasket issue, or are those studs screwed into the head?

vstech · #2 11-01-2021, 11:36 PM

Usually the issue here is with wear in the valve cover bosses.

Shern · #3 11-02-2021, 01:21 AM

Quote:

Originally Posted by vstech

Usually the issue here is with wear in the valve cover bosses.

I'm not entirely sure what you mean here.

By "boss", are you referring to the bolts that seem to be collecting oil?
What form would wear take? In the threads, in the fit of the studs(they don’t wobble)?

And if so, what can be done?

Rogviler · #4 11-02-2021, 02:32 AM

My diagram to the rescue:

The "bosses" would be where the cover sits (the two small red areas). I'll let someone else explain the wear thing, since I haven't heard of that. If anything, the way the cover contacts the studs can interfere with how well the gasket seals, but the fix is filing them shorter so the gasket is pressed tighter. Sounds like it might be a different issue than that.

Shern · #5 11-02-2021, 12:30 PM

Thanks for the Diagram.

I guess I still don't understand where the oil is coming from.
I found a part number for the studs: 6160160070 which suggests to me that they
could possibly have backed out a little. Going from nothing, to all four corners is a little fishy... doesn't suggest wear to me.

gregp1962 · #6 11-02-2021, 07:12 PM

The round part the screw passes through should not be exactly even with the edge of the valve cover. It should be about 1mm lower. I filed mine down as in the picture and tread below. Mine is now not leaking.

Valve Cover Modifications for OM617

Shern · #7 11-02-2021, 07:38 PM

The leak isn't coming from the gasket though. It's coming from those studs.

Unless I'm missing something obvious, the gasket is sealing just fine.

BillGrissom · #8 11-03-2021, 12:01 PM

I agree that filing down the bosses on the aluminum cover won't stop your leak. That is to insure even clamping pressure on the rubber gasket at the head, but that isn't where yours is leaking oil. I don't think you want a gap, rather metal-metal contact, bottoming out on the bosses, but compressing the rubber enough to seal.

I don't recall the wave-washer shown under the nut, but seems parts that could easily get lost. The stud is outside the gasket, so don't know where the oil would be coming from. You might be right that it comes past the threads of the stud into the head though strange if that tapped hole isn't blind. As a quick fix, you might put a resilient washer under each nut, like nylon. Change one at a time so you don't lose your seal. Do you have a lot of blow-by pressure when you try the "oil fill cap dance" test?

Shern · #9 11-03-2021, 03:38 PM

Quote:

Originally Posted by BillGrissom

I agree that filing down the bosses on the aluminum cover won't stop your leak. That is to insure even clamping pressure on the rubber gasket at the head, but that isn't where yours is leaking oil. I don't think you want a gap, rather metal-metal contact, bottoming out on the bosses, but compressing the rubber enough to seal.

I don't recall the wave-washer shown under the nut, but seems parts that could easily get lost. The stud is outside the gasket, so don't know where the oil would be coming from. You might be right that it comes past the threads of the stud into the head though strange if that tapped hole isn't blind. As a quick fix, you might put a resilient washer under each nut, like nylon. Change one at a time so you don't lose your seal. Do you have a lot of blow-by pressure when you try the "oil fill cap dance" test?

Thanks Bill.

I still have all four wave washers installed but they're no longer very wavy.
I looked again this morning, and it's actually the two studs on the passenger side of the engine -the two that run behind the gasket- that are wicking oil.
On the other side, the gasket is weeping on the front corner. It's only a year old, but who knows, maybe I got a funky one.

Re: blow-by pressure, cap stays on. This is something that has only just begun, which leads me to believe something backed itself off, or jiggled loose.
I'll likely change the gasket for good measure, but the pass side studs are what concern me.

Rogviler · #10 11-03-2021, 07:17 PM

Just for information: the wave washers are there because the torque on the nuts holding the cover is so low (if you do it right) that heating and cooling changes how much pressure is applied to the gasket. The wave washers are intended to even out this pressure and prevent leaks. They also help keep the nuts from backing off. I believe they're intended as a consumable item and are cheap to replace each time you have them off.

Shern · #11 11-04-2021, 11:55 AM

That's good info, thanks Rog.

I typically torque to about 11ft/lbs. I'll see if I can find some new washers...

vstech · #12 11-05-2021, 05:57 AM

I’m sorry, I meant if the cover is over torqued the soft aluminum can be damaged. Inspection of the bosses in the aluminum may reveal cracks, or mushrooming from over tightening.

Shern · #13 11-06-2021, 04:00 PM

Thanks VSTech.

I took the cover off this morning to take another look and install some fresh wave washers.

The stud channels on the valve cover make direct contact with the studs screwed into the head. That point of contact is not finely machined. It's amazing it didn't leak sooner. I was half tempted to install .5mm copper crush washers on all four studs (below the the valve cover, but chickened out, having no sense of whether the additional mass would prevent adequate clamping pressure upon re-torquing the cover.

ykobayashi · #14 11-06-2021, 04:36 PM

Quote:

Originally Posted by BillGrissom

I agree that filing down the bosses on the aluminum cover won't stop your leak.

That’s funny. It stopped mine. Those are the photos of my cover above. I recognize my trash can.

Mine were really grunged up from overtightening. I think one or more were worn more than the others and it made the valve cover tilt to one side. Flattening the bosses out forced the valve cover to lay more flat.

Hard to describe. The studs on the engine side had actually crushed indentations into the aluminum bosses on the cover. So the four were no longer at the same level so to speak. I think filing them down allowed me to level it out and thus kill my oil leak.

Shern seems to be saying his studs are leaking. That is a new one to me. Maybe they need to be pulled out and slathered up with RTV and threaded back in?

vstech · #15 11-07-2021, 09:05 AM

Quote:

Originally Posted by ykobayashi

That’s funny. It stopped mine. Those are the photos of my cover above. I recognize my trash can.

Mine were really grunged up from overtightening. I think one or more were worn more than the others and it made the valve cover tilt to one side. Flattening the bosses out forced the valve cover to lay more flat.

Hard to describe. The studs on the engine side had actually crushed indentations into the aluminum bosses on the cover. So the four were no longer at the same level so to speak. I think filing them down allowed me to level it out and thus kill my oil leak.

Shern seems to be saying his studs are leaking. That is a new one to me. Maybe they need to be pulled out and slathered up with RTV and threaded back in?

Keep in mind, the intake side of the cover has the stud bosses inside the gasket… so damaged bosses will allow oil creep up the studs due to blow by.
It’s unlikely he studs themselves are causing the issue… no WAY I would put RTV inside the bosses… you’d never get the cover off for the next valve adjustment without breaking the valve cover…