I've known for about two years and 10,000 mi that my 617-powered 300D turbo's #2 cylinder exhaust valve is leaking and probably "burnt" (thanks for the valve adjustments, PO). However, since there is no noticeable difference in performance compared to my other 300D-T besides hard cold starts, I haven't bothered to do a valve job. Compression is on average 300-350 psi with #2 at 200 psi. My block heater and 20% biodiesel have made it relatively easy to start even at 0F.

Is there a risk involved in operating an engine with a known leaking valve due to erosion of the valve seat? I'm worried that I'm slowly eroding metal out of my head with the high hot gas velocities through the leaky valve. Are valve seats typically replaced anyway during a cylinder head rebuild? I'm trying to gauge whether I should go ahead with a valve job now, or if I can rod the engine a few more thousand before I finally make the plunge.

Thanks,

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Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)

I would do the head rebuild as soon as you can. It's my knowledge that valves will usually give first, most engines are designed this way! At least they were as an engineer for the Chrysler Corporation! The head has cooling jackets in it but a valve does not and this is the reason you replace valves before replacing valve seats or the head.

I need to get mine done too!

I thought that the hollow exhaust valve stems on my Mercedes were (spelling?) sodium filled to aid in cooling them? I was also told in trade school NEVER to cut them apart as the sodium can react violently.

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84 300D, 82 Volvo 244Gl Diesel

Yes sodium filled valves will explode in water, but the bottom line here is that the valve will take the brunt of the damage. Not to say this can't get expensive! Valves are going to cost money too, but not as much as a new head. I would still do a head overhaul as soon as possible, but if your like me, dependent on the vehicle at the moment, this is sometimes easier said than done.

Yes, and ounce you get inside of something you almost always find something else that needs to be fixed to. Best to do it when you have plenty of time.

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84 300D, 82 Volvo 244Gl Diesel

Yes. Further and expensive damage will occur. If that valve got burnt its already given that it's toast, relatively cheap and easy to fix now. Continued driving will indeed eat a non machineable groove into the seat. (similar to a broken ring in a cylinder) Valve seats are typically just reground back to original seat angles when rebuilding a head, they are only replaced when they cannot be repaired. You want to try to avoid the need to replace seats, as replaced seats are known to have tendencies to loosen from heat cycling and can fall loose, wedging a valve down, and you know the rest....
This was a common occurrence back when unleaded gasoline came into play and people would replace the soft seats in their "regular" (leaded) gasoline engines during overhauls.

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Chris
64 190D R.I.P.
80 240D W/617 engine -for sale
82 240D -for sale

All right, I guess it's time.

So, whats involved when going at the valve job?...I mean what parts should be replaced on principle while I'm in there.

Should I replace all my valves, or only the exhaust valves since one of them is burnt (or only the burnt valve itself)? Valve guides & seals? And then, what to do about the prechambers...should I pull them to inspect & clean? I'm sure turbo drain seals would be a good idea. Any other items I'm forgetting?

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Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)

Just rebuild the entire head, strip it to nothing and replace everything. Dont forget to redo the valve seats and redeck the head.

Just tell your machine shop you are not selling this car and you want it fixed right and let them tell you what it needs. If you have a good machine shop you trust, this will not be a problem. The nice thing about these heads is that the valve turns a little bit every time it opens so as to eliminate hot spots and erosion to a point.

Also replace the prechambers? I always get myself into these situations where "I might as well do it while I'm in there"

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Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)

I would let your machine shop make recommendations here. Tell them the current mileage and ask what it needs now that you have it apart. Are you doing all the work yourself? Rebuilding a head is really best left to a quality machine shop!

Yes, I was planning on pulling everything apart and only having the shop machine the valve seats for me. I assume I will need to find a machine shop that has some MB knowledge though, especially if I run into trouble. It's fun to DIY (most of the time)

Special Tools Required
injector socket - have
12 point socket for head bolts - have
prechamber wrench & slide hammer - have
valve seal installation mandrel - need
valve guide removal/installation tool - need

What else am I missing from my list?

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Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)

" I was also told in trade school NEVER to cut them apart as the sodium can react violently."-- Diesel911

VERY TRUE...do not cut them on a lathe, do not cut them with a torch,do not cut them open, ETC...


"Yes sodium filled valves will explode in water,"--Knightrider966

Where did that come from ? Saying only that makes it sound like Diesel911's statement only applied to getting the sodium wet... Don't heat the sodium valves, cut them open , etc...... just avoid them... Greg

Just ship the head to Metric Motors. Mike will strip it and advise of what should be replaced. He tends to be very conservative..........anything that looks even slightly off the spec will receive the "replace" recommendation. He will suggest replacing the prechambers and he'll likely suggest replacing the valve springs. The exhaust valves are usually below spec and the intake valves are marginal. The valve guides and the valve seals are toast. Make sure he gets OE valve seals.

What you decide to do is dependent on how long you expect to run the engine. If you want another 150K...........all the recommendations should be followed.

Sodium will flare rapidly when exposed to moisture, cutting them open will cause a flash fire, and if dropped into water, sodium will explode!

Some manufacturers like SAAB for instance will recommend that the machine shop disposing of burnt and unsalvagable valves drill into the center exposing the sodium and them dropping it into a tank of water to eliminate the metal fragmentation hazard.

Science 101.