OE Exhaust Valves, Sodium Options

[914werke]

I know Jake suggests tossing these, but unfortunantly Im rebuilding a set of heads. Id like to keep them stock, but Im more concerned about longevity.
Is there anything that can be done to improve thier function?

Cryo? (IMG:http://www.914world.com/bbs2/html/emoticons/sad.gif)

[jsteele22]

Interesting thread, had no idea it was gonna be so contentious. I've got no opinion one way or the other, but I thought I'd add a few things to the mix.

The issue with exhaust valves is not getting them too hot. Filling them w/ sodium, as was mentioned well down in this thread, is to make the valve a good conductor of heat. You want the heat to flow from the head of the valve where temperatures are highest down the stem to where it can be conducted out of the valve. Not only is sodium a good conductor, but (as mentioned) it melts at really low temperatures, so there is also some convection going on.

Stainless steel, by comparison, is a fairly crappy conductor of heat. I'm guessing that what has changed over lo these many decades is that good SS valves strike a happy balance between having slightly better thermal conductivity and also being able to survive higher temps.

So what's the big deal with sodium exploding ? Simply put, it combines with water (H2O) and grabs the OH, releasing the H (hydrogen) in the form of a gas. This process is exothermic, meaning it also releases a fair amount of heat. So if you combine sodium, water and air, you might get an explosion. If you want an explosion, use lots of sodium in a small amount of water. Actually, the reaction is so fast, that a smallish chunk of sodium will skitter around on the surface of a pond due to all the hydrogen gas streaming out. Kind of like a mosquito having a fart attack. If you don't want an explosion keep the sodium away from water or air or both. If you read in the manuals of cars that have sodium filled valves, you might be suprised to find the recommended means of disposing of them : grind through the valve until you hit the sodium, then drop it into a bucket of water ! Is this crazy ? Not really. The amount of sodium is small and the valves are heavy. They sink to the bottom, the water reacts with the sodium until its all gone, and the hydrogen bubbles out to the top of the water, cooling off very rapidly. Unless you intentionally try to ignite it, it will just diffuse out into the air.

Carry on.