Looks like I need to replace the tensioner gasket on my 1981 300SD as it's leaking oil. I've searched and found a few relevant threads but no write up on how to do this. Is it just a matter of removing the 2 mounting bolts and the end bolt for the exhaust manifold? Any need to remove the large bolt with the spring behind it?

Once it's ready to put back in, I've heard it might be necessary to install the tensioner in stages (only for turbo models). Can someone elaborate on this? Thanks.

Did I ask a dumb question?

I mean, it looks straightforward and I'm inclined to just remove the tensioner as one piece, replace the gasket, reinstall the tensioner as one piece. I'm only being cautious as I don't want to grenade the engine by screwing up the tension on the chain.

There is 2 possible sources of leaks. The cap that holds the spring in and the tensioner housing to head.

The tensioner housing to head will have 2 O-rings or a paper gasket depending on which it is setup to use.

For a non-turbo
If it was me before removing it I would screw out the Spring Cap first pull out the spring and inspect that as the coils if the spring can wear on the out side.

Also inspect the plunger for excessive wear. Then remove the Housing.

Reinstall gasket or O-rings (either held in place with grease). Install housing and torque. Assemble the plunger + spring and an new Crush Washer under the spring cap.

Instructions for the turbo ones are similar but the piston on the turbo one can only go one way. So remove the spring cap and crush washer, remove spring and inspect. Remove the tensioner housing.
push out the piston/plunger from the spring end.
Install new O-rings, install housing to the head and torque. Lube up the ratchet grooves inside of the tensioner housing. Install the plunger/piston just enough to get it centered. Install the spring with the new crush washer and spring cap. That should be sufficient to safely push in the plunger/piston.

The above is just a guide. It would be better if you pulled up some other threads to compare and or look in the actual Manual.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the response. Not everyone has a manual and there really aren't any other threads that I've found that go into detail on this.

So it looks like I'll have to remove the large bolt and the spring before removing the housing, huh? I was hoping not to have to mess with that as my chain tension is just fine. Not a big deal either way, I guess.

People have posted online sources of the Mercede's Service Manuals.

Some people have issues with the fact that the free sites might be violating copyright issues. However, Mercedes did offer an newer version of the Service Manuals for free if you signed up for it. Don't know if that still apples.

So if Mercedes is offering similar information for free I personally don't see the copyright issue.

Personally speaking back in 2007 when I first bought my W123 I was desperate for information. I bought the CD set of the Manuals which no won't work on my newer computer as it is 16 bits and I paid too much for it. However, having the service manual has saved me time, trouble and money. Later I bought the actually used Books and found out the Books actually have more in them.

While there is lots of good advice on this forum it is a good idea to try to locate several versions of how to do the job you are going to do.

As an example there is a Wiki instructions on changing the rear wheel bearings. In the instructions it has to use a large punch and drive the Hub. Using a punch on that part of the hub most often damages the thin threaded area. It swells it or otherwise deforms it.
A new rear wheel hub about 5 years ago was $350.00 and to go to the junk yard get another hub is even harder then doing that in your drive way (it is easier just to take the whole rear lower control arm).

Again personally I like to know how it is done in the Service Manual and then I like to read how others have done it. Then I decide what I am going to do.

Also note that making a mistake on installing the Timing Chain Tensioner can damage the Engine.

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84 300D, 82 Volvo 244Gl Diesel

Mercedes still hosts the FSM for free:

https://www.startekinfo.com/StarTek/outside/12253/?requestedDocId=12253

Make sure you're using a desktop computer and Firefox or Chrome as your browser. It will NOT work with a phone or tablet.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

My 1984 & 85 300D's sound different, since no need to remove any exhaust manifold parts, but you do need to remove the T-stat housing. My EGR valve may interfere (mine are gone). The internal spring is usually worn flat on one side, so have one ready (<$10 here at P-P). Also have a new gasket and T-stat gasket, plus a good time to change the large T-stat bypass hose (I used silicone).

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Pic of a worn tensioner spring.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel