1983 240d zero compression #3 stuck intake valve

[petecooke]

I have a 1983 240d with zero compression on the #3 cylinder. Car has about 200k miles. All the other cylinder messure between 340-400 compression.
I pulled the motor about 6 months ago and it's been sitting in my garage since then.

I squirted some oil in the #3 cylinder and the compression instantly jumped to over 300 psi so I assumed I had bad rings/piston/cylinder.

Yesterday, I pull the valve cover and set the cam so that there was valve clearance between both the intake and exhaust valves. I assume by doing this both valves would be seated tightly and there would not be any air coming out of the intake or exhaust ports.

After doing the above, I shot forced air into the injector port and all the air came out the intake port. I did the same thing to the other cylinders and the cam/engine rotated as should happen if the valves were seated.

Now I think the problem has always been with the intake valve on #3.

The questions I have are the following:

Why would squirting oil in the #3 cylinder cause the compression to go to over 300 if the intake valve is stuck open?

Is it possible to fix this problem without removing the head?

Will a machine shop need to rebuild the head or is this something I would be able to handle with the proper tools? I do have many tools/gauges but not a commercial press.

What should be my next step in resolving this problem?

Thanks for any advise.

pete

[kerry]

A 0-300 change after adding oil wouldn't indicate bad rings or cylinders. It would be something like 200-300 change because bad rings or cylinders wouldn't result in a 0 compression, just lowered compression. 0 has to be either a hole in the piston or head or a valve not sealing.
I'm not sure why adding oil would cause the valve to seal unless the valve is just sticking in the guide as opposed to being burnt and the oil lubricated the stem enough to cause it to seal. Or, you put enough oil in there to cause a kind of hydrolock situation and the oil pushed up against the valve forcing it shut.
It's possible you could replace just that one valve and solve the problem. Depending on your economic situation it might be wise either to do that or just get the whole head done at a machine shop while it's off. Replacing a single valve while the head is off is not a big deal. Take off the valve spring, push the valve out, put in the new valve and put back the valve spring. Of course, the much bigger question is why the valve wasn't sealing to begin with. Is it burnt? Is the stem bent? Is there a problem with the guide? Does it just have a weak valve spring? If it's just a weak valve spring, that problem can be solved without removing the head by replacing the valve spring.

[Stretch]

Originally Posted by petecooke

...
After doing the above, I shot forced air into the injector port and all the air came out the intake port. I did the same thing to the other cylinders and the cam/engine rotated as should happen if the valves were seated.

...

Is it possible to fix this problem without removing the head?

Will a machine shop need to rebuild the head or is this something I would be able to handle with the proper tools? I do have many tools/gauges but not a commercial press.

What should be my next step in resolving this problem?

Thanks for any advise.

pete

If you are at all unsure about the valves being closed or not I recommend you remove the rocker arms.

By doing this you will be able to see the relative heights of the tops of the valves more easily. You will also know for sure that the valves are as closed as they are going to get.

Please note that by removing the injectors you are now meant to replace the little sealing washers that fit between injector and pre-chamber. So that's something for the shopping list. If you have a handy adapter it is often "cheaper" to apply compressed air via the glow plug holes.

Is it possible to fix this problem without removing the head? No sorry - you'll have to take the head off to remove the valves.

I would talk to a machine shop about doing any machining work required.

[petecooke]

Thanks for the replies. Both responses make a lot of sense. I guess the first thing to do is to see if the valve spring is good. If it is good, then I will pull the head and go from there.

[Stretch]

Originally Posted by petecooke

Thanks for the replies. Both responses make a lot of sense. I guess the first thing to do is to see if the valve spring is good. If it is good, then I will pull the head and go from there.

On a worn valve guide and worn valve stem seal the valve can more easily drop into the combustion chamber. To stop this from happening you can position the piston close to TDC - resting the valve on top of the piston crown will do no harm so long as you don't turn the crank!

Good luck and let us know how you get on.

[barry123400]

Is there a chance you never checked the valve lash when/after the problem occured? If the valve lash where too tight there would be virtually no compression. Maybe tired adjustment nuts?

With the engine out you adjusted lash clearance into that valve. So now you have compression and the oil thing was just circumstance. Just being a little cautious here and trying to make sure you consider everything before pulling the head.

I at the same time for your mental health hope this is not so but still had to mention it. In my opinion it might take quite a shot of oil to manage the hydralic effect closing that valve with just air pressure giving a very slow revolution of the engine. Broken valve spring might enable this as well.

You are going to possibly be doing enough work that the absolute cause of why that valve was open has to be well identified. This car had not been sitting for a very long time just before you used it? A big hunk of carbon or something on the seat might have disloged as well. Unlikely but do you have constant compression of that cylinder now with no oil added?

[t walgamuth]

Oil can seal a bad valve sometimes. I agree that bad rings will not result in zero compression.

[petecooke]

Barry,

The valve clearance was adjusted before the engine was pulled. I checked the clearance since it's out and it's still within specs. When I shot compressed air into the cylinder, I could visually see the clearance between both the intake and exhaust valve.

I was also thinking about a piece of carbon stuck under the valve but I would think that would break off with the hot motor running.

I was thinking about spraying PB Blaster in and around the valve tomorrow to see if the valve will loosen up. If I could get the valve to seat, the problem could be solved.

I'm also wondering if I increase the intake clearance greatly, would that pull the valve tighter and maybe seat it correctly?

I'm skeptical about it working but I'm going to give both of these a shot before I pull the head.

Thanks for the reply.

pete

[Diesel911]

X2 on the Valve Adjustment.

If you put enough Oil into the Cylinder it is possible for the Oil to make it up to the Valves and get onto them; because the small clearance the Piston Head and the Cylinder Head.

[barry123400]

You know the seat and the valve face are probably okay. Otherwise I doubt you would have gone as high in compression as you did. A bent or warped valve stem seems not too likely especially on an intake valve unless the timing chain was thrown some time ago. Or some part of the prechamber got loose and became located between the seat and the face of the valve.

An exhaust valve stem with low lash could warp from heat though I suspect.

Anyways a new compression check of that cylinder with no oil added seems indicated to me. If by chance you are pulling the injector inspecting the condition of the pre chamber for being totally intact might be worth doing.

What you are describing is fairly unusual in these older design diesel engines. The oil hydralic effect I decided may not have been a factor. The piston with the oil would have to travel all the way up the bore with the valve closed to get your high compression number once it came back.

I wonder if any kind of effect like this might occur with a very loose valve guide. Mercedes are known for occassional loose guides. If you have compression on the next check and the valve spring is intact I would examine that valve guide very carefuly. Although in my opinion it would have to be very very loose. The spring pressure could then tilt it enough for the valve not to seal usually at operational speeds. This is a reach though. Actually I am out of ideals at this point.

[barry123400]

Originally Posted by petecooke

Barry,

The valve clearance was adjusted before the engine was pulled. I checked the clearance since it's out and it's still within specs. When I shot compressed air into the cylinder, I could visually see the clearance between both the intake and exhaust valve.

I was also thinking about a piece of carbon stuck under the valve but I would think that would break off with the hot motor running.

I was thinking about spraying PB Blaster in and around the valve tomorrow to see if the valve will loosen up. If I could get the valve to seat, the problem could be solved.

I'm also wondering if I increase the intake clearance greatly, would that pull the valve tighter and maybe seat it correctly?

I'm skeptical about it working but I'm going to give both of these a shot before I pull the head.

Thanks for the reply.

pete

Increasing the clearance would pound the valve stem a little harder but no benifit I can think of. Introducing air pressure again with both valves having lash space. You should hear where the air is going. Either out the intake, Exhaust pipe, or oil filler hole. This if your next compression check is zilch. I kind of think the next compression check of that cylinder may be normal. I just re read all the posts and see you did already determine where the air was coming from. So it is definatly something to do with that valve.

[petecooke]

Barry,

I think it's definitely a problem with the intake valve on #3 since air is coming out the intake when there is clearance on both the #3 cylinder intake/exhaust rockers.

I will do another compression test tomorrow and post what I get. I will also squirt some oil and see if the compression reads greater than zero.

I'm going to squirt some PB Blaster around the #3 intake valve to see if it loosen anything and allows the intake valve to seat.

Thank for all your help.

Pete

[petecooke]

I sprayed PB Blaster on the #3 intake valve but that was useless. I removed the valve spring on the #3 cylinder and pulled the valve up to it tapped the top of the cylinder. I spun it around multiple times to try and get a seal but when I added compressed air into the injector port, the air just blew out the intake port.

Tomorrow I will pull the head and see if I can determine why the valve is letting air get by it.

I was crossing my fingers hoping I didn't have to pull the head but no such luck.

I will update this post when I pull the head.

Thanks for all the help.

Pete

[Codifex Maximus]

Hmm... after readiing the foregoing, I have a theory:

You probably are having a valve not seal properly in it's seat.

With air, it's so low viscosity that it would probably come strait through with little resistance if a good seal is not achieved. However, you got 300 compression due to the higher viscosity of oil.

Did you detect oil coming back into the intake as well?

[whunter]

Originally Posted by petecooke

I sprayed PB Blaster on the #3 intake valve but that was useless. I removed the valve spring on the #3 cylinder and pulled the valve up to it tapped the top of the cylinder. I spun it around multiple times to try and get a seal but when I added compressed air into the injector port, the air just blew out the intake port.

Tomorrow I will pull the head and see if I can determine why the valve is letting air get by it.

I was crossing my fingers hoping I didn't have to pull the head but no such luck.

I will update this post when I pull the head.

Thanks for all the help.

Pete

Please post pictures of what you find.

Thanks


.