Hello, I took the cylinder head off the 85 300TD wagon due to a blown head gasket and found a broken exhaust valve guide on cylinder #2.

Is it common to need to have the valve seats replaced in these engines This one has 600,000 kms?

I have been told by a machinist that quoted some work on this head (mainly for installing new guides) that the exhaust valve seats need to be replaced. I was surprised by this....

He mentioned something about critical tolerances because it is a diesel? Would these tolerances be factored when adjusting the valves, after the seats are re-ground?

We were also told that he would need to bore the old ones out and try to find new ones.
He emphasized "TRY" to find new ones that would fit... maybe this is typical and I don't know any better, but, am a little bit apprehensive of boring equipment being used and, would much rather make sure we can find the proper sized seats before any boring starts to go on with this head. Wagon heads are not common in these parts. The seats don't look that bad to me except for the one that had the broken guide, and even that one is not too bad. He did say the seats were pounded out. I did a solvent test and they all held solvent.... even the one with the broken guide, although it has been worn slightly on one side.

I want to believe him but, also wanted to check here first, as maybe we are missing some information on this type of cylinder head and they would indeed be out of spec. as far as the "critical tolerance is concerned"

I am guessing that he means the valve would be too far recessed into the head after grinding...making some dimension on the top side with regards to valve-train configuration out of wack. I thought maybe this could be worked out with the valve adjustment....but am not sure??

Another machinist told me that Mercedes case hardens the head and once wear occurs past the case hardening then the valve seat wears faster.

This seat removal/install adds a considerable price to the bill. Where can seats be found for this 617 turbo motor if they are needed?
Thanks.

If you take a look in chapter 05-291 you'll see that the FSM says you can skim the head and then re-seat the valves. There are limits to how far the valves may stick out and how far the seats are recessed compared with the mating surface. The FSM doesn't mention how thin the overall thickness of the head may be.

I'd print that out and gently show it to the machinist. There's no need to suggest you're telling him how to do his job...

...but well there seems little reason to my mind why you'd be installing inserts for new seats from the information you've posted above.

If you still have the head post up some pictures of the valve seats as they are now - I'm sure someone here will say "oh oh! there's something wrong there"!

Compared with some engines of the same era the OM617 is made to fine tolerances but by modern standards I'd expect most engines to be made just as "tight"!

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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!

Here is the FSM page Army is talking about.
http://www.w124performance.com/service/W126/w126CD1/program/Engine/617/05-291.pdf

Print this out and take it to your machinest. If your machinest is not a mercedes buff I bet he would love to see the FSM and would love to keep it for future use.

Looks like the seat cut into the iron that the head is made of. they do case harden these types of seats. and as the head wares it is possable to ware through the hardend serface and into the soft iron. the solution to this is to install a harened steel ring. These rings are bought by size and then the head is bored for the size of the ring. then the ring is machines to spec for the engine.

Even if all your seats are good other then the one with the cracked guide, it may be wise to install all new seats at this point. Most machinests I know if they are going to have to go to the trouble to install seats for one valve will tell you to do the whole head. Its not like its an easy to access part of the engine, and it does ware, so if your in there and have the head in the machine its easy to do the job 5 times over. It would suck to fix the one valve and then have prblems down the road as the others ware.

This page has some good pics of how the old seats are bored out and new seat installed.
INSTALLING VALVE SEATS

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Thanks guys.. I did send this attachment to the machinist that I decided to go with. They quoted me to replace just the exhaust guides but has now changed his mind and he wants to do all of them....of course for much more money. The latest price I have heard is $750.00 and we will have a pretty much fully rebuilt cyl. head as far as machining goes. This is what he is doing...

All new guides
all new seats bored and installed (of course complete valve job)
resurface deck of cyl head(they say it is warped .007)
Checked for cracks(magnaflux)
pressure tested
cleaned and degreased
re-using valves except the valves in the number 2 cylinder with the broken guide. I took the head off my spare motor and gave him a whole other set and he said he would pick the best ones
I was talking to Roy and he said to see if they will resurface (light skim) the mating surface for the intake/exhaust manifold....I took out all the studs and mentioned the idea to them. He never said if they would do it for sure so we will see how it turns out...hopefully soon...but not too soon as I still have parts to clean for reassembly. I haven't heard from them in a week....

They did mention that it pressure tested out o.k but they found small cracks in the prechamber bores. I made sure to ask them if they leaked and they said no so I am hoping that is o.k Is it normal to have cracks in the pre-chamber bores?

p.s
Army...I went out to take some pictures for you but the camera was acting funny...I think I broke it somehow or maybe some oil got into it when it was out in the garage... cause they turn out all blurry when viewing them on the camera and the fully recharged batteries don't want to work so I can upload them to my computer...I'll get some up when ever it is I can remember to get batteries next time in town.