Leaking exhaust valve cyl. #1 240d

[stephenc1984]

I have a 1978 240d with a bad exhaust valve.
It has over 200,000 miles on a non working odometer and was my daily driver.

The problem started a while ago when I noticed that the car was hard to start.
After doing a compression test and a valve adjustment the number one cylinder had 115 psi where the other 3 cylinders were between 225 and 250.
I pulled the engine and it has been sitting for about a year.

Now that I have time, I recently pulled the exhaust and intake manifolds and sprayed soapy water in the valve ports with it on TDC on the 1 cylinder and applied compressed air through injector hole.
Lots of soapy bubbles seeped out of the exhaust valve.

I then removed the head (of coarse marking the chain and sprocket to keep time With the head removed, to the naked eye, I cannot tell that the suspected bad valve is any different than the other three.
However, after putting more soapy water in the valve port, it leaks through the valve without any pressure behind it other than its' own weight sitting in the port.

My question is what to do next.
Do I replace just the one valve or all?
How much does it cost to have it re-machined and such.

I can get my hands on a junk yard head for 60 bucks or so but I don't know if I should take that gamble.
What do you think?
Thanks in advance!

[barry12345]

Since your compression test was not the greatest overall. Plus you pulled the engine if I am reading your post properly. I think you might source a better used engine compression wise for less than the head work at a machine shop.

By the time you buy a new head gasket and whatever to reinstall another used head plus the cost of a good used head once again you just might get a whole better engine.

Can you still see much if any cross hatching in the cylinders from the factory? It all is kind of a trade off depending on the overall condition of the car as well perhaps. First of all I would do the other valves with the soapy water test. You may find simular results.

Compression loss on the number one cylinder can have causes that cannot be overlooked. I already have a suspicion that the number one bore and piston may have more wear. Perhaps there is much less cross hatch in that bore than the other three. A quick test of the bore rings pistons etc with the engine head off may be the flow time for say a certain amount kerosene to clear each cylinder when poured in. Certainly not conclusive but may indicate something. Running the 616 with no fuel filter changes or low fuel pressure in the base of the injection pump will put a lot more loading on the number one cylinder. This of course will increase it's wear more over time than the other three. Or this is my belief. In my opinion you have some thinking to do.

[stephenc1984]

Originally Posted by barry12345

Since your compression test was not the greatest overall. Plus you pulled the engine if I am reading your post properly. I think you might source a better used engine compression wise for less than the head work at a machine shop.

By the time you buy a new head gasket and whatever to reinstall another used head plus the cost of a good used head once again you just might get a whole better engine.

Can you still see much if any cross hatching in the cylinders from the factory? It all is kind of a trade off depending on the overall condition of the car as well perhaps. First of all I would do the other valves with the soapy water test. You may find simular results.

Compression loss on the number one cylinder can have causes that cannot be overlooked. I already have a suspicion that the number one bore and piston may have more wear. Perhaps there is much less cross hatch in that bore than the other three. A quick test of the bore rings pistons etc with the engine head off may be the flow time for say a certain amount kerosene to clear each cylinder when poured in. Certainly not conclusive but may indicate something. Running the 616 with no fuel filter changes or low fuel pressure in the base of the injection pump will put a lot more loading on the number one cylinder. This of course will increase it's wear more over time than the other three. Or this is my belief. In my opinion you have some thinking to do.

I didnt know that low fuel pressure could effect the #1 cylinder in that way. I always do regular maintenance. However, who know how it was taken care of before i bought it. Also, I have already put Marvels oil in two of the four cylinders to see if anything gets past the rings or at the very least will clean them.

[barry12345]

Originally Posted by stephenc1984

I didnt know that low fuel pressure could effect the #1 cylinder in that way. I always do regular maintenance. However, who know how it was taken care of before i bought it. Also, I have already put Marvels oil in two of the four cylinders to see if anything gets past the rings or at the very least will clean them.

All 616s especially should have their fuel pressure in the base of the injection pump checked with a gauge or prefferably a permanent gauge installed. Normal maintenance can certainly help but this low pressure can exist totally unnoticed over the years. In humans it is simular to high blood pressures going unoticed. Yet this can cause disaster over time.

This all goes back to a member years ago asking me why I thought only the number one rod bearing fails quite commonly on the 616 engine. I really had to struggle with this to locate the why of how it happens. This was so hard on my limited intelligence that at times I wished he had not asked. I can get like a dog with a bone on ocassion.

Over time what I eventually came up with becomes more and more certain. That the old generally thought reasons or causitives where fairly quickly ruled out did not help much. . It was not totally a design fault or mercedes would have eliminated it.

What did amaze me is they did not put a lift pump with the same pressure as the turbo engines on this block for the last years of it's production at least. Essentially this engine and varients of it are very old and where in production for a very long time..

Since the 616 engined cars where at their lower end perhaps they did not pay enough attention. Right or wrong a couple of people in europe have said it is not a problem over there. The primary diference is their european injection pump reacts a little different somehow on the 616s when exposed to low fuel supply pressure if that is true.

We and some french cars got our type of north american injection pump. It operates just fine as long as the base fuel pressure feed is kept up.

[Doktor Bert]

In most cases, the valve guide will be bad also. A used head may be better, or worse than what you have. Sometimes, your budget just won't afford a proper repair. If this is the case, then perhaps weigh the cost of the used head against what a reputable shop would refurbish your head for.

In general, I will re-use intake valves on a budget, but I NEVER re-use exhaust valves...

[barry12345]

For example I have an excellent spare 616 engine on hand. Since it is worth little I will retain it. I kind of figure maybe a hundred and fifty dollars would find a simular one either in a wreck or pick and pull yard. I will never buy a head or engine off a vehicle. Or on the ground as the expression goes. Unless I intend to rebuild it. Or I know for certain the milage is truly very low.

On a used engine if I were to pull a sixty dollar head. Since I assume you would do a compression check before pulling the head. If it were good buying the whole engine might be considered. Or I would consider it in your situation.

My considered guess is the soapy test on the other valves on that head you have off will not be much better. Of course I am probably wrong and you can prove it.

I also have a curious component in my nature. The results of a pour test on that block would be both interesting and perhaps helpful to others later. In a way it is a long shot but perhaps possible and otherwise.

[stephenc1984]

Originally Posted by barry12345

For example I have an excellent spare 616 engine on hand. Since it is worth little I will retain it. I kind of figure maybe a hundred and fifty dollars would find a simular one either in a wreck or pick and pull yard. I will never buy a head or engine off a vehicle. Or on the ground as the expression goes. Unless I intend to rebuild it. Or I know for certain the milage is truly very low.

On a used engine if I were to pull a sixty dollar head. Since I assume you would do a compression check before pulling the head. If it were good buying the whole engine might be considered. Or I would consider it in your situation.

My considered guess is the soapy test on the other valves on that head you have off will not be much better. Of course I am probably wrong and you can prove it.

I also have a curious component in my nature. The results of a pour test on that block would be both interesting and perhaps helpful to others later. In a way it is a long shot but perhaps possible and otherwise.

What should be the compression in the other cylinders? I thought 250psi was a good number? The interesting thing about this motor before it was pulled is that the only indication that something was wrong was the hard start in the morning. Once the motor warmed up it ran smooth. It would seem with a cylinder with 115 psi the engine would lope, but it did not. It is difficult to judge how much power the engine had because the engine lacks power from the start. I will do the soapy test on all the valves and post some pictures tomorrow also.

[barry12345]

[QUOTE=stephenc1984;3058206]What should be the compression in the other cylinders? I thought 250psi was a good number? The interesting thing about this motor before it was pulled is that the only indication that something was wrong was the hard start in the morning. Once the motor warmed up it ran smooth. It would seem with a cylinder with 115 psi the engine would lope, but it did not. It is difficult to judge how much power the engine had because the engine lacks power from the start. I will do the soapy test on all the valves and post some pictures tomorrow also.[/QUOTE

Great. We all share in what we do. A few years ago I suggested we would all become more comforatable with the injection pumps and it actually happened. A gravity type leakdown test in comparison on at least some cylinders including the number one might become a usable test.

I always wanted to pretty well diagnose an internal engine issue before taking the head off as a couple of times I was left basically looking at things trying to establish what was really wrong. So i quickly kicked that habit.

Two hundred pounds pressure or two hundred and twenty pounds is probably getting near the practical bottom for overall compression pressure. They will still run but not as efficient as all cylinders over or around the three hundred pound mark. Cold starting will also be hampered to some extent. A good tight 616 engine should product in the neighbourhood of 350 pounds compression test pressure. One of my 616 engines is almost new. It fires off so easy it does not require glow plugs in reasonable weather. If it turns over it is running.

[Diesel911]

Originally Posted by stephenc1984

I have a 1978 240d with a bad exhaust valve.
It has over 200,000 miles on a non working odometer and was my daily driver.

The problem started a while ago when I noticed that the car was hard to start.
After doing a compression test and a valve adjustment the number one cylinder had 115 psi where the other 3 cylinders were between 225 and 250.
I pulled the engine and it has been sitting for about a year.

Now that I have time, I recently pulled the exhaust and intake manifolds and sprayed soapy water in the valve ports with it on TDC on the 1 cylinder and applied compressed air through injector hole.
Lots of soapy bubbles seeped out of the exhaust valve.

I then removed the head (of coarse marking the chain and sprocket to keep time With the head removed, to the naked eye, I cannot tell that the suspected bad valve is any different than the other three.
However, after putting more soapy water in the valve port, it leaks through the valve without any pressure behind it other than its' own weight sitting in the port.

My question is what to do next.
Do I replace just the one valve or all?
How much does it cost to have it re-machined and such.

I can get my hands on a junk yard head for 60 bucks or so but I don't know if I should take that gamble.
What do you think?
Thanks in advance!

I like this idea; and it is new to Me.