Getting ready to do the head gasket on 350sdl w/ 245k on the clock. I have read so much on this forum about this vehicle, so thanks for all before me. I hope to get some pictures and share with others this journey. Great ride that was well taken care of before I purchased. I heard that Mercedes diesels go forever, so I was unaware of the problems the 350 carried. Other than oil in the coolant the vehicle shows no signs of terminal problems yet. After the head is off, I should know for sure the fate of the vehicle. Productive suggestions are welcome.

With the head off, check piston rise above bore. I forget the spec, but it is something like min 0,785 to max 0,935mm. (verify before check) This will tell you if you have any bent rods.

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Chief

1991 350SD

Chief: My desktop has gone down, so my CD copy of the manual is MIA. I have torn down to the head. So far the gasket looks solid, so it was a surprise. I have sent the head for eval before doing any machine work. How do you measure the piston rise without losing TDC? That is my only concern. I will be posting pictures shortly. Thanks

There is a procedure for establishing tdc on #1. I lent my FSM to someone so don't have it at the moment. Hopefully someone can post?

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Chief

1991 350SD

I have attached the pictures from the head removal. The vehicle was sitting about 3 weeks before the head was removed. The head gasket showed no signs of a break or compromised integrity . This worried me greatly, since it narrows the causes down to a possible costly realization.

From the pictures you can see that #4 cylinder is full of antifreeze. Also the valves for that cylinder seem to be cleaner than the rest. Brake cleaner was sprayed on that area to see if any visual cracks were present. Feeling the valve surface it was realized that there was a lip near the outer edge. So it maybe that a head gasket replacement had occurred but the head wasn't serviced. That could explain the poor seal and leaking of coolant. The old owner has passed on, so no one to ask about the service history.

If you look at the exhaust side, you can see 3 of the ports with antifreeze. This makes me feel that the head maybe cracked. I will find out soon enough on the head when the machine shop tests compression.

I havent checked the clearance on the pistons and will be re-buying MB FSM. That should help determine my course of action along with the head status. Any suggestions and interpretations are appreciated.

Guess it didnt post my photos: Round 2






https://www.dropbox.com/sh/makcdd59c26ny63/20ewA0x84l

Hmm, still no pics. Did you consult the online service manual? You should also be able to find the TDC procedure there.

I'm hoping you just have a gasket issue. Since our cars depend on such high compression ratios, it's critical to get the sealing surfaces dead clean and properly prepped, use only an MB oe gasket, and scrupulously follow the head bolt torque procedure.

I have an excellent used head if you find you need one- Hopefully you won't!

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Chief

1991 350SD

With all that coolant in the cylinder, it should have hydro locked, unless you just happened to catch it before bending a rod. I also have a few questions about the procedure. Please do not think I am trying to ridicule you by asking them. I am a diagnostic nerd and love the figuring out part only to be confirmed as correct during tear-down.

1) Did you drain the coolant before pulling the head?
2) Did you perform a cooling system pressure test or cylinder leak down test before you pulled the head?
3) Was this engine running when you acquired it?

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Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi

Arghhhh . . . I should have shop done this to mine. I've got mine torn down and getting hoists today to remove head. It had small amount of white smoke, was getting hotter than normal (not dangerously high though) and was using about a pint of coolant a day.

Was there a something "special" to do to get the head free from the block? Mine won't budge. The service manual says use a hoist - so I figure it must go straight off of some pins.


oops - Just noticed your's is a 6 cylinder. Mine is a 5.

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Brad
1981 300TD - daily driver
1963 Chevy II
2001 F-250 7.3 Power Stroke

Make sure you have removed the row of head bolts that are hidden below the cam bearing towers. Other than that it should come off easily.

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Chief

1991 350SD

Mach:

1. Coolant was drained.
2. Compression test was performed after I found out about the trouble these motors had. The numbers were around 375 psi for all of them except one (dont remember which one maybe #3 or #4) was about 345psi.
3. Engine had been running but they stopped the vehicle because the belt came off. Helped install the belt and she ran fine.

After I found coolant in reservoir that is when the thoughts ran through my mind. I began researching and ended up doing a compression test to identify an issue. I braced myself for a new motor after reading all the stories/hear say on this motor. Since the compression came back within a decent range for the age, I was happy to be a lucky one... maybe too early a celebration!

Ok Pics seem to have loaded!

I will be getting the manual today, but have a long week since a vacation is lined up for next week. I hope that I can complete a lot of this before I leave. Thanks for the offer... lets hope I wont have to take you up on it!

For the prechambers... can they be reused. Will the machine shop clean and prep those? If I get the ok on the head and piston height, I will get valve guides and other items the shop suggests.

So, I called the machine shop to find out the status of the head today. Said that it didn't check out when they pressure tested it. I guess that the fear finally came true. How likely is it that the rods are bent? If the head is cracked would that have given the work done an escape route rather than take it's toll on the rods?

*How much does a head usually go for?
*What tools do I need to ensure that the rods arent bent & Im wasting my time.

The limiting step is my funds at the moment and I have to pick and choose projects wisely. Damn sure hate a reality check!!

Used heads are all over the place. I have seen them from $400 up. A new head is over $2300, and does not come fully machined!

All you need to measure piston crown rise above bore is a vernier/dial caliper with foot attachment. You could also use a linear dial indicator and stand. You could even get away with a precise steel rule, but that will be a judgement call.

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Chief

1991 350SD