So I've been working diligently on the pursuit of a vanishing point, a classic Diesel Mercedes with no oil leaks!

I did the turbo drain tube/check valve/oil pan gasket, and got the bottom end sealed up pretty well, and I did the valve cover gasket as well. I noticed a couple drops coming from the back of the engine, and saw oil around the injectors which traced back to the valve cover gasket.

I figured I'd try simply tightening the valve cover bolts a bit more, to see if it helped. Three of the bolts tightened up really well and all looked promising, upon tightening the 4th(rear passenger side bolt), I noticed the bolt wasn't getting any tighter, just sort of turning stiffly. I immediately feared something was stripping, I started going left, and thought I was backing the bolt out, but I noticed there was a lot of resistance, and it didn't seem to be loosening off of the stud. I marked a side of the stud, and realized the stud is just turning with the nut.

Ugh. I pulled it into the garage and am planning to tackle this tomorrow. I read what little I could find which says that you can removed the stud and use a bolt the right length that goes from the valve cover into the head. That's fine by me.

However, my fear is, would the threads in the head itself that held the stud down have stripped? I mean, I would hope that Mercedes would use very strong threads on the head itself, but I'm just wondering.

In addition, anyone else who's ever dealt with this? Maybe have any tips for me working it out?



Thanks guys!

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1984 Mercedes-Benz 300D

There are a few threads on this subject out there. I don't have them to hand though...

...from what I can remember most of the problems seem to be nut and stud related rather than stud and head related. But you'll have to just go and see - good luck.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

If something is stripped, it's the stud.

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83 SD

84 CD

most likely, the stud let go. these studs have a thread shoulder, and the nut goes down only so far. I bet the stud is sheared at the head.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
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1987 190D 2.5Turbo
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1987 300TD
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Use a Dremel-type tool with a cut-off wheel to cut a slot in the top of the stud. Then hold the stud with a screwdriver to get the nut off.

Even if the threads in the Head are stripped it can be fixed with a Helicoil. But as often is the case these sort of things happen in the worst possible location making it harder to do the job with success.

I don't know if they have the correct size you need but PepBoys sells Metric and SAE Helicoil type re-threading sets over in the area where the Tools are hanging. It has the Drill Bit, Tap, threads and the installer Tool.

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84 300D, 82 Volvo 244Gl Diesel

Well, it all went about as well as it could've. Upon removing the other 3 bolts, the valve cover came right out. The lower part of the stud that goes into the head was completely stripped anc came right out.

At first the threads in the head apeared to be about 8mm of smooth, and then threads below that, which I knew wasn't right. I deduced that the top of the threads were filled with crud and bits of the old bolt that had been turned and smashed so much, it had made a smooth spot. I took one of the bolts that I had bought, and used a grinder to cut "reliefs" into it, for the crud to gather in. Then I got the bolt started in there, and turned it with a nice big wratchet, making sure to take it out every few turns and make sure I wasn't doing any damaged.

Sure enough, my little gamble worked out quite well. As I turned the bolt, the bolt threads forced the crud out of the threads in the head. Then the crud was able to just build up and sit in the little "reliefs" I had grinded into the bolt. Every time I took it out, I cleaned it off, and went a bit lower. Now I have nice, clean threads that I can turn the bolt into by hand.

However, I bought bolts that were way too short, so I measured about how long I'd need, and how deep the threads go down into the head. I'll try to get a bolt as long as will fit so that it can use the most threads and spread the load out.

Does anyone know if there's any dis-advantage to just pulling all of the studs and using bolts into the head all around?

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1984 Mercedes-Benz 300D

The only thing that I think you need to be aware of is that you shouldn't over tighten the valve cover - you might damage it. There's a smaller chance of that happening if you use the original bolts...

...however if you are persistent enough I'm sure you can damage it if you try.

If you want to check for flatness of the mating surface of the valve cover and you don't have a nice smooth surface plate to hand place the valve cover on some modern glass (like a big window) to see if it is still true.

The valve cover gasket should be fitted just the once...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Gotcha. Well I have a torque wrench so I can keep track of the pressure I tighten the bolts. I wanna say I read that they shouldn't go over 10 ft/lbs but I'll have to verify that.

And that's a good idea, I'll check to make sure the valve cover is still true.

As for the one time gasket use, this was a new gasket. I know that doesn't mean much since I've used it once, but I'm gonna use it with some grey RTV sealer and see what I get. In a lot of the reading I did about the valve cover replacement, people were recommending a think coat of gasket sealer.

So I'm going to clean the surface real well, and assuming the valve cover is flat, I'll put a think coat of gasket sealer on there and give it a try. If it still leaks, i'll just order a new gasket on my next parts order and put it in there. it can't leak any worse then it did before. haha Besides, I've pulled that valve cover so much, I've come to enjoy it.

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1984 Mercedes-Benz 300D

My choice would be to skip the part about the RTV sealer I reckon that would just make a mess - but hey if you are enjoying yourself go for it! Car mechanics should be enjoyed and not just performed in cold rain by the side of the road...

The FSM - chapter 05-210 (valve adjustment) says

15 Nm for valve cover nuts on the OM615 / 616 / 617.91 / OM617 turbo

In old money that's 11 foot pounds.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

As long as the gasket isn't hard and the sealing surface is clean, it should work fine. Skip the RTV.

Haha, I like that attitude! I plan on laying down a small bead, and then flattening it out with a scraper, basically just so that there will be a thin, sticky little layer. If anything, it'll hold the gasket onto the valve cover a little better and keep it from falling off during installation.

And I must've read the 15Nm and made the rough calculation of 10-11 ft/lbs. Close enough for me. Thanks!

In theory it should. But even before I had the bolt issue, I had put a brand new gasket in there during my valve adjustment, and gotten everything tightened down right, and it still seeped a bit. Granted, I didn't check to make sure my valve cover was flat, I do need to check that. But I did clean the surface on both ends and all, and it still wasn't totally oil tight. My first car was a Mustang that I did a lot of Gaskets on, all of which required RTV. Working on that car, I got pretty good at applying RTV, so it's no trouble for me to try it. haha

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1984 Mercedes-Benz 300D

If you are going to replace the stud with a bolt, you could use the right sized washer between the valve cover and head. The stud has a foot which sets the gasket squish.