M117 Sodium filled valves

[OldMercs]

Has anyone ever experienced failure of the sodium-filled valves on an M117 in a high-ouput or high-mileage situation? I've read about non-Mercedes cases where an engine builder will discard sodium-filled valves in a souped up engine claiming that they become a weak link in such an application.

[bgkast]

The 617 turbo-diesel engine has sodium filled valves too. I have never heard of this issue, and 300K plus miles is not uncommon for them.

Biggest thing to watch out for is if you have them ground...and use water for the lubricant.

[vox_incognita]

AFAIK all diesels since the introduction of om621(early 60-ies) have sodium filled exhaust valves..never heard of such problems....

[t walgamuth]

i am guessing it might be from ignorance on the part of the engine builder.

i think the benzes have used them on racing engines about forever. the promote the valve living longer due to surperior heat rejection, i believe.

tom w

[bgkast]

Originally Posted by vox_incognita

AFAIK all diesels since the introduction of om621(early 60-ies) have sodium filled exhaust valves..never heard of such problems....

The 616 and naturally aspirated 617s do not have sodium filled valves. AFAIK the first production MB diesel to use them was the '78 300SD (first year of the turbo 617).

[psfred]

I believe all the diesel engines have sodium filled valves, not just the turbos. None of the gasoline engines do.

The usual "stupid engine builder" problem with exhaust valves is to use an aftermarket steel exhaust valve guide, bored out way oversize, instead of the correctly sized (very tight) factory BRONZE guide.

Massive oil consumption in 10,000 miles or so, every time.

Peter

[dillonkbase]

im not sure thats accurate, my book for the 220 series 1959-65 says"it should be noted that sodium filled exhast valves are fitted to all models covered by this manual" which only contains data on the gasoline engines

[vox_incognita]

Browsed the engine service manual last night,my om621 has sodium filled exhaust valves "for better heat dissipation"...and the warnings..."do not cut...etc." ...so I assume every diesel on(maybe gas engines too)have them...

[MTUpower]

om 616 and om617-912 engines DO NOT have sodium filled valves.

[Tomguy]

I have a 3.5/4.5 exhaust valve in front of me - (A 116 02 (logo)) stamped on it.
I've always believed they were sodium-filled because, if not, their stems would likely be as narrow as the intake valve stems. They are narrow at the top but widen shortly after - most likely for the sodium. IF I were feeling daring I'd cut into it to see - but I will not take that chance, thanks!

[Strife]

I've always though this was amazing - the sodium might turn liquid inside at operating temperatures, acting as a "heat pipe" to the rest of the valve train, directing heat away. Breeder nuclear reactors were designed to use liquid sodium as the working fluid!

You don't want to cut these because sodium reacts immediately in water (and more slowly in water vapor), emitting hydrogen, which sometimes explodes from the heat of the reaction. Very exciting.

[Mr Basil]

I replaced a burnt exhaust valve a few weeks ago and during the process replaced a loose exhaust valve guide for a M130 gas engine. I needed a mandrel for installation and used the upper part of the the old valve. I used a metal cutoff wheel to cut the valve stem. Nothing happened when the sodium was exposed, initially, because I didn't cut so fast as to make the metal red hot. But I was curious and zipped through the job which began a bright molten sodium frothy sputtering reaction. I tossed some water on it to cool it down ( I didn't want the metal heat-distorted) and the molten sodium was knocked off and raced around in little fire balls on the surface of the water. Sodium reacts vigorously with water. Dousing in oil is supposed to be way less exciting.
One valve part I set aside where the sodium slowly oxidized to a whitish powder over the course of a couple weeks. I needed the other part for my mandrel and wanted to fully discharge the sodium so it wouldn't unexpectedly interfere with my valve guide installation, burn down the house or something, so I put it under the kitchen faucet where the water caused the sodium to leap out and race around in little fireballs in the sink. The sink wasn't empty and I found that burning sodium likes to stick to tuppaware! I also lit some foam produced and it ignited in a non-spectacular way so I would guess hydrogen.
The sodium apparently is solidly filled inside the valve so I'm guessing it melts and conducts the heat way more effeciently than solid metal. Melting point is around 98F I think. It's a fat valve so it might set up convection currents.

Basil

[Tomguy]

Keep in mind that when sodium reacts with water it doesnt produce just hydrogen. It produces something much more dangerous.

(2) H2O + (2) Na = (2) NaOH + H2

Sodium Hydroxide (NaOH) is the strongest base there is. Also known as lye, this caustic material is a major ingredient in drain cleaners like Drano, and can cause severe skin burns as well as rapidly oxidize most metals.

[Roncallo]

Originally Posted by OldMercs

Has anyone ever experienced failure of the sodium-filled valves on an M117 in a high-ouput or high-mileage situation? I've read about non-Mercedes cases where an engine builder will discard sodium-filled valves in a souped up engine claiming that they become a weak link in such an application.

I would guess two things:

1) When building a race motor you want the lightest valves possible to avoid high RPM float or excessive spring pressure. Sodium filled valves hava a larger diameter stem, more than likely increasing the total weight.

2) When building a race motor you want the least amount of obsticals in the way of airflow in the intake system. It is not uncommon to neck down stems in race motors. The larger diameter stem of the sodium filled valve is an obstruction to airflow.

John Roncallo

[t walgamuth]

my 62 190c fintail had sodium filled exhaust valves.

tom w