i have a 1984 300sd turbo 124k miles. all the sudden it slowly started running like crap.#3 cylinder exhaust valve went way out of adjustment holding the valve open. readjusted as needed and ran the vehicle for approx 500 miles and now its slowly running like crap again. anyone ever see a valve seat loosen up or a valve mushroom on one of these engines?

Sounds like the adjusting locknut is not tightened completely.

I've heard that if you let the valves run held open for some period of time, that after an adjustment it takes awhile for the valve to pound back into the valve seat cleanly. There's apparently some carbon buildup that needs to get crushed outa there.

Don't know if I believe it all that much. But what I like to do is when I get a new car that turns out to have tight valve clearances, I adjust the valves a little bit wider than specification. Not much, just in between the spec gauge and the next one up on the feeler gauge.

After you get some mileage on the car with the correct valve clearances, it seems to stay in adjustment much better.

So, you need to get the valve cover off again and check 'em.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I'm so glad I have a 601.

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1984 190D 2.2 Auto 220k
2001 Jeep Cherokee Sport 70K
2004 Lexus RX-330 ??K
2005 Chrylser Crossfire LTD 6K

Play guitar? Go to www.cyberfret.com for free online lessons!

locking nut was tight.
ken that makes sense. im going to readjust it one more time and if it happends again im going to have to remove the cyl head and inspect. thank for the reply

I've always thought that as the valves wear the clearances get wider. On every kind of car that I have owned that had adjustable valves, I've always adjusted the valves just slightly on the tight side (about .02 to .05 mm depending on the clearance spec) so it would give me slightly quieter valves and a little extra time between adjustments. I've only owned my M-B for a little less than a year and its my first one. Would this philosophy get me in trouble on a M-B?

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

Yes.

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I'd better go readjust my valves in the M-B NOW!

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

my advise would be never to start the engine again until you've pulled the head and replaced the valve which is beginning to stretch where the stem meets the valve head and is about to break and send its head through a piston top. Now, you aren't talking about a VW and M-B diesels probably don't use the kinds of valves which were the problem -- the VW problems were valves which were welded up from two pieces to have the perfect alloy for long wear on the stem and a different alloy perfect for high temperatures on the head, and if the clearance went to zero from long neglect, the leaking gases would cause the weld joint to weaken. Nevertheless, if I saw a valve on any motor which tightened up its clearances several times at short intervals, my VW/Porsche training and experience would cause me to panic.

Valves MUST contact the head, not only for sealing, but as a critical part of the cooling process. If they are tight, they don't cantact the head and you won't get the 500,000miles+ these engines are famous for!

lietuvial- these 617 engine valves tighten the clearance over time
unlike other car manufactures which loosen and start ticking.

fimum fit- i think you hit it on the nose. thats the only thing i can come up with. i bought this car 2 months ago with a cracked radiator. im thinking now that the original owner may have slightly
overheated it. when he said he caught it before the needle reached red. im in the process of a complete engine rebuild on a 123 non turbo. once i finish that im going to yank that head off for inspection. thanks all for your help