I just went to adjust the valves on my 1984 300SD (412,000+ miles) and got to valve 4. I did all the others and it went well. This is not my first time. I bought this car in 1998.

Anyway, here is my problem. The number 4 won't adjust. I think the cap nut has bottomed out. Have I lost my mind? Am I forgetting something after doing this a bunch of times in the last 14 years?

I loosened the cap and log bolts. Turned the lock bolt clockwise to gain some clearance. Turned the cap bolt clockwise to adjust the valve clearance and...nothing. Repeated several times until the cap bolt turns the valve and there is still distance between the lock and cap.

Do you have the cam lobe positioned properly?

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

If the Nut is Moving and the Valve itself is not moving the Nut may be stripped.

If the Valve is moving one of the Nuts is stuck to the Valve. You need to get something to hold onto the Valve Spring Retainer so it will not turn and try to loosen the Nut.

If the Nut and Valve are still turning when you have a good hold of the Spring Retainer it could be the Tab on the Spring Retainer that fits into a Groove in the Valve at the top has busted off.

See the DIY section for ways to hold the Spring Retainer.
DIY Repair Links
http://www.peachparts.com/shopforum/forumdisplay.php?f=82

http://www.peachparts.com/Wikka/DoItYourSelf

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84 300D, 82 Volvo 244Gl Diesel

Does the star spin also?

If so, you need to hold it while you adjust the nut.

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83 SD

84 CD

I held the spring retainer while moving the lock nut. When I turned the cap nut clockwise, it finally stopped and and then started turning the valve and retainer.

I'm guessing it can only go so far down. Both nuts move freely until then.

I get a good hold on the retainer when moving the cap nut also. The nut won't move any further.

I believe so. Same as always perpendicular to the rocker. It always seems to be at 1 o'clock.

I am not sure what is going on.
However, you can position the Camshaft So that the Rocker Arms on that Cylinder (Exhaust and Intake Valves) are both positioned on the circular part of the Camshaft Lobes. At that point the Piston is at least Close to Top Dead Center on the Compression Stroke.
After that you can loosen the Rocker Arm Bolts and remove the whole Rocker Arm and Brackets assembly. (I did this to all of the Rocker Arm Brackets/Assemblies when I replaced my Valve Stem Seals.)


That should leave you plenty of room to fool with the Valve adjusting Nuts so you can see what is going on.

If the Piston is up near Top Dead Center (you should be able to tell by the Came lobes) if you remove the Nuts on the Valve the Valve may Drop down.
But, it should not Drop too Far.
However, it still is a good idea if you can to avoid letting it Fall. If your Valve Stem Seals are still a little tight they will hold the Valve up if you do not move it around very much.

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84 300D, 82 Volvo 244Gl Diesel

Here is what I see. The valve stem is almost .25 inches higher than the one next to it. I'm guessing the valve is pulled up into the head somehow. I had a Toyota that did that.

That would assume both intake and exhaust valve stems are the same length.

Valve guides are replaceable but valve seats are ground into the head.

I think it is time for a picture - can you upload one for us?


In the mean time

When was the last time work was done on the head?

Have you had the valve stem seals / valve guides / head replaced recently?

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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!

Remove the Nuts and measure it that way. If the Valve is much higher as you say it is time to pull the head off.

I have not ever had a Mercedes Engine apart or read anything as to the length of the Valves so cannot comment on if Exhaust and Intake are the same length.

I can say this from the other Diesel Engines I have had apart the Valve Seats are generally in much better shape than the Valves and the Exhaust Valves take the worst beating.
If the Valve really much higher than the other Exhaust Valves I would expect to find the Valve Face to be in bad shape and thin.

I forgot to mention that the more there is more detailed instuctions in the DIY section on changing the Valve Stem Seals will keep the Valve From Dropping too far into the Cylinder after the Nuts are removed.

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84 300D, 82 Volvo 244Gl Diesel

Ok. Let me try this Imgur upload.






I've never done any work on the head. Honestly, I just adjust the valves and enjoy the ride. No seal or guide replacement in the 14 years I have owned it. 412K on the engine.

Valve 4 on the right (exhaust) is the culprit. Measured from the top of the stem on both. Valve 3 is 1 1/8" tall. Valve 4 is 1 3/8

[QUOTE=Diesel911;2912308]Remove the Nuts and measure it that way. If the Valve is much higher as you say it is time to pull the head off.


Don't have that option right now. Since it runs fairly well and just smokes, I may just go as far down as possible and tear it down when it gets too annoying.

A difference of 3mm - hmm that doesn't sound too great.

I've checked some specifications for you. The valves on the turbo OM617 should be 131.5mm long => same for either the intake or the exhaust valves.

What you could do is put the piston to the top of the bore and remove the valve springs for both valves. So long as the piston is at the top of the stroke the valves won't fall in. You could then measure the heights of the valves again to see if it is a valve seat problem or not. Whilst you're at it you could then compare the condition of the two rotocaps...

I'm hoping for you it is a rotocap - nice easy fix if it is!

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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!

By rotocap, I'm guessing you mean the cap nut? They are fine. I even switched them to make sure.

No under the valve spring there's a thing that spins (called a rotocap)...

The valve should close up against the seat in the head. If the valve spring is so old that it doesn't compress as much as it should then the valve might not be closed when you are measuring the clearance. If the rotocap is squashed / collapsed then you've got the possibility of a similar problem.

I'm thinking that you've either got one valve higher then the rest or 9 valves lower than they should be!

If you've got one high one then I'm betting you've got a valve seat problem. Not good news...

Some more data for you =>

The valve spring should be about 50mm long when unloaded (I can give you the exact length you should have if you pass on your spring colour codes).

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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!