TheSamba.com :: View topic

Sun Oct 28, 2007 12:45 pm

Just fond these:
http://www.csp-shop.de/cgi-bin/shop2/shop_main.cgi?func=start&wkid=5444553888
And I can't find any info on them, so could someone please explain the idea behind sodium filled exhaust valves?

Sun Oct 28, 2007 12:47 pm

It's been a while since I've read up on it, but I believe the sodium turns into a liquid when it gets hot, and it helps pull the heat from the face of the exhaust valve and encourages it to disipate into the stem/head. I know the sodium is there for heat reason, but I may be off on my function.

Sun Oct 28, 2007 12:57 pm

Bashr52 wrote: It's been a while since I've read up on it, but I believe the sodium turns into a liquid when it gets hot, and it helps pull the heat from the face of the exhaust valve and encourages it to disipate into the stem/head. I know the sodium is there for heat reason, but I may be off on my function.

That's right. To add a little: It's the sloshing of the liquid sodium in the valve which carries heat from the valve head to the stem, then through the guide, etc.

Sun Oct 28, 2007 11:35 pm

Sodium filled exhaust valves are commonly used in light piston powered aircraft.

Mon Oct 29, 2007 12:59 am

People say they're prone to beakage (T4 usage), but I also know that Cosworth put them in the YB engine. My buddy had a Sierra with one of those and a chip that put the power at something like 285hp...
I guess it's a different world with the aircooled engines, being that they run so much hotter than the water pumpers. Maybe that's why folks say they have issues, cause they never gave any trouble on the water cooled YB. Not that I'm aware of, anyhow.

Mon Oct 29, 2007 1:00 am

Personally, stainless is cheaper, and trouble free. I'd use stainless before sodium any day (on a street car, that is).

Mon Oct 29, 2007 11:36 am

They were used in heavy duty truck engines also. It was always rumored that if you intensionally ground into the valve stem, that they would blowup. Probably untrue, but I never wanted to try it to see.

Mon Oct 29, 2007 11:42 am

I've also heard that, wonder if it's true? Also, none of the machinists I've talked to were willing to grind them either, said I had to get new ones point blank, then all they would do is lap them into the seats.

Mon Oct 29, 2007 11:46 am

toomanytoys wrote: They were used in heavy duty truck engines also. It was always rumored that if you intensionally ground into the valve stem, that they would blowup. Probably untrue, but I never wanted to try it to see.

They won't blow up, but don't let the sodium come in contact with your skin, or water!

Mon Oct 29, 2007 11:59 am

If I remember correctly, they were also used on the 1965 Porsche 356SC.

Thu Dec 27, 2007 5:22 pm

I've had many 350 Chev heavy duty motor soduim valve heads as well as other makes in my machine shop, they have larger diameter stems than light duty heads. They rarely wearout guides compared to light duty heads which wearout guides very quickly when used in heavy duty applications. I wonder if vw soduim valve stems are a larger diameter? I would like to try some.

Fri Dec 28, 2007 12:46 am

Geb wrote: If I remember correctly, they were also used on the 1965 Porsche 356SC.
914/4s too.

WVbugman wrote: I wonder if vw soduim valve stems are a larger diameter?
They are stock 8mm. But don't worry, they are hollow. The metal that would be in the center adds nothing to any bending strength the stem may have. Reduction in tensile strength is minimal.

Fri Dec 28, 2007 12:46 am

There are 2 main ways an exhaust valve is cooled, through conduction when it is in contact with its seat and through conduction through the stem to the head. The sodium improves this 2nd heat conduction.
Porsche used sodium filled valves on some 80's aircooled 911's.

Fri Dec 28, 2007 7:21 am

16v vw's also use these.

Sat Dec 29, 2007 9:42 pm

I had a 57 Chrysler flat head in my first boat that had sodium filled valves, the shop manual said if you replaced them to should "bury" the old ones to dispose of them!