So to be clear: The valve CAN drop if the retainer is not held down?

Also, please confirm: To make sure the cylinder is at the top of its cycle to prevent the valve from dropping, I need to set the cam so that the intake lobe is directly up and the exhaust valve is to the right...i.e. towards the drivers side?

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1984 300 SD 384,000 Miles

Or should the intake lobe be directly to the right?

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1984 300 SD 384,000 Miles

correct.

FYI:
This morning I used a box cutter slipped under the old nut to catch the valve threads (prevent valve drop) for the few seconds of swapping nuts.

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Great, thanks for the help. I am going to try this during the afternoon today and will report back. I'm assuming the exhaust valve will be straight up since the exhaust must be leaving the cylinder when the piston is at the top of its cycle. Going to remove the injectors and feel for the piston with a metal wire just in case.

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1984 300 SD 384,000 Miles

Be sure to replace the injector heat shield with a NEW one, when you are done.


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Not a good plan. Better to use the TDC markings on the balancer. Observe the orientation of the cam for cylinder #1 when at TDC, then replicate that picture for the cylinder in question.

Or…mark the cam sprocket every 72 degrees and rotate to the appropriate cylinder in injection order.

qwerty didn't tell you why so I will. The injectors are screwed into a pre-combustion chamber which will not allow access to the top of the piston.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Did you see why he wanted to remove the injectors?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I am out of time, preparing for the Mercedes owners club area at the Concours d’Elegance of America Sunday..

I figured correctly that one of you would note the issue.
I doubt he has the special tools for or wants to pull the pre-chamber.

I am surprised nobody has mentioned removing glow plugs to make it easier to turn the engine.
FYI: With the glow plug removed and a compression test adapter installed, you can apply compressor (100 PSI) air pressure to hold the valve


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What is TDC?

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1984 300 SD 384,000 Miles

top dead center, when the piston is at the top of its stroke.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The crankshaft needs to be at OT for cylinders 1 and 4:



or on the opposite marking (180º opposite) for cylinders 2 and 3:



The cam lobes of the particular cylinder need to be pointing upwards (on both sides of the oil pipe):



If you remove the lock nut, the valve will drop onto the piston. If you are not sure or want to be extra careful, put a tie rap tightly around the valve stem (through the spring) before removing the lock nut. The tie rap will prevent the valve from dropping if you have done something wrong and the piston is not at the top position.

So if both lobes are up like that am I 100% safe?

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1984 300 SD 384,000 Miles

The thing is I don't have compressed air nor do I have any understanding of when the valve should not fall. Someone told me that when the exhaust valve is straight up and the intake valve is pointing to the right, that the piston will be at the top of its cycle. However, after rotating the engine it is physically impossible to get this orientation for cylinder number 4. Any thoughts?

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1984 300 SD 384,000 Miles

Govert, are you using special tools in the first two pictures or is that a marking that is somewhere in/around the engine? If it is something that is there, from what angle are those pictures taken from...ie should I be looking at the back or the front of the engine, etc.?

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1984 300 SD 384,000 Miles