Head Gasket and other items on 300SDL - PeachParts Mercedes-Benz Forum

tstarr · #1 07-10-2004, 04:34 PM

I just got back from the local DIY session with the Mercedes Club at a local MB dealer. Ouch! I was looking at a transmission leak and planning to do some basic maintenance, I was told that the following needed to be done to my car -

1) Replace the head gasket. It was clearly leaking.
2) Replace the Secondary Pump
3) Replace engine shock and spring (minor)

And various other minor things.

The biggest concern is the head gasket. I've done a search on this and am not sure if I should take this on myself. I'm a heavy DIYer (in more ways than one), but this seems like a big deal. They absolutely did NOT recommend me doing the secondary pump and that seems like the easier of the 2 big jobs.

Any thoughts on the head gasket as a DIY job? I did this on an Oldsmobile I had once, but I also had to ditch the car about 3 months later because it blew again. That time, I also replaced the cracked head with a rebuilt unit and it sucked, so I don't know if that's a fair basis to decide.

I'd be very interested in any DIYer advice/experience on this. It's the original head (number 14 on the head itself). Thanks for any input.

Sooty Taillight · #2 07-10-2004, 04:44 PM

I may or may not do the same myself to my 603. I have been told on this forum that to change the head gasket, you must first remove the cam. This is where it gets tricky! There is a special sequence to remove the cam and if it is not followed to the letter, according to MB, you will bend or snap the cam!

While this is not impossible to do if you can get the info, and follow procedure, it just might be worth it having a MB specialist do it!

Wonder what they charge?

tstarr · #3 07-10-2004, 05:51 PM

I'm going to do some cost compare Monday. I'm going to call the MB dealer and my favorite independent to get some ballpark figures. I know that it will depend on what they get into when they see it. And the indy hasn't looked at the car yet, but I want a ballpark to start with anyway.

Hatterasguy · #4 07-10-2004, 05:57 PM

How is your headgasket leaking? Mine has a small oil leak in the front, that just makes the front of the engine a little dirty.

What is the Secondary Pump?

If I ever had to do my headgasket I'd do it myself, just take your time pulling the cam and do it the proper way. Cam's don't just bend they are a big chunk of metal.

tstarr · #5 07-10-2004, 06:01 PM

The shop foreman looked at it from underneath and the back of the engine. He showed me an area toward the back where it was leaking coolant and oil out onto the exhaust and the sheet metal back there. I've noticed a slow coolant leak that I haven't been able to nail down, but I go through it at a steady pace. There was also some black in the coolant recovery tank which he said was oil mixing in with the coolant.

Before I had my indy do it, I'd have him check it out for a second opinion. He's always been honest, so I would be comfortable with his opinion on this.

sixto · #6 07-10-2004, 07:11 PM

Pulling a 603 head is no big deal. There is a sequence to loosening and tightening the cam bearing bolts but it's less complicated than the head bolt tightening sequence.

If the secondary pump is the injection pump. That's not a terribly complicated job either but you need special tools or a keen understanding of pump timing to get it set again.

Engine shock and spring? On the serpentine belt?

Sixto
95 S420
87 300SDL

engatwork · #7 07-10-2004, 07:17 PM

The secondary pump is not the tranny pump is it?

tstarr · #8 07-10-2004, 08:05 PM

It's on the transmission, attached to the right rear side of the transmission body. He always called it the secondary pump. He also thought there might be some leaking on the other side, around kickdown switch, but the majority of it was on the right side.

tstarr · #9 07-10-2004, 08:07 PM

Sorry, I just saw the reply on the engine shock. On this engine, there are 2 items mounted on the front of engine, one is a little shock and the other looks like a shock, but appears to be a spring with a rubber hose around it. The engine was vibrating and he set his wrench up against the shock and the vibration noise stopped.

sixto · #10 07-10-2004, 08:27 PM

I don't know about vibration but when the bushings in the belt shock go bad the engine sounds like it has rod knock.

Sixto
95 S420
87 300SDL

tstarr · #11 07-10-2004, 09:40 PM

sixto, I think that's the part I was talking about. Yes, the sound was more like knocking. He took a wrench and set it right on the top of the shock and the knocking sound went away. So I guess it's really the belt shock. I'm still learning about this engine...

dieseldiehard · #12 07-10-2004, 10:39 PM

That is the serpentine belt tensioner, right in front. OM603 engines tend to lose that item regularly and the result can be a busted timing belt (resulting loss of water pump and alternator all at once and the engine will be in dire straights.)
Presuming you go ahead to replace the head gasket, I suggest you plan on having the head sent to a head shop to check for cracks in the critical areas where the early heads sometime fail. And they will perform a skim cut to make certain the head is perfectly flat. If there are cracks or corrosion spots that are too deep for a skim cut you will possibly need a new head, just be aware of that.
As long as it is off the engine you should have it checked at least.
I lucked out with a rebuild on my '87 300D turbo with #14 s/n head at 250K miles there were only a couple of small corrosion areas, nothing major, and the head was flat within a few mils before surfacing. A new head gasket and it is back in fine running condition, no more leaks.
The cam on these engines can be broken that is a known issue. The lifters apply a lot of force on the cam and if one goes to remove it without following the proper sequence the cam will break.
DDH

tstarr · #13 07-10-2004, 10:44 PM

Thanks for all the info. Yes, it only makes sense to get the head checked before putting back on, especially since this is one of the originals. There were a couple of other things mentioned, like a leaking bellows over by the turbo, but all they mentioned was minor compared to the head gasket.

I'm going to monitor the trans fluid for the next little while to see how bad the leaking is. The trans gasket had loosened up and it was leaking around there, so I don't know how bad the pump leak is at this time.