New Heads VS total rebuild on C8OE CJ heads - Your opinions?

[66FAIRLANE]

What was the reasoning behind filling them with sodium?

[Heo]

Heat dissapation.  Spelling??

[66FAIRLANE]

Still don't get it. How would a different substance trapped all round help heat dissipation? Must be missing something.

[plovett]

A valve with a hollow sodium filled stem dissipates heat faster than a valve with a solid metal stem.  I believe the sodium conducts heat better than the metal around it.

At running temperatures the sodium liquefies in the valve stem.  So you have the heat of combustion transferring heat to the head of the valve, the metal in the valve conducts heat into the stem.  The stem conducts it into the liquid sodium where it's conducted away from the head of the valve up toward the other end, and then into the guides, cylinder head, and even the rockers.  All this to keep the valve head cooler.  I think sodium filled valves are still used in some applications.  Maybe turbocharged industrial applications???

Anyway. I think the whole idea is that liquid sodium is a very good heat conductor.

Someone who knows more about it can say it better and/or correct me, but I think that's the jist of it.

paulie

[plovett]

Still don't get it. How would a different substance trapped all round help heat dissipation? Must be missing something.

Maybe this is more directed to your question.  Think of the liquid sodium as a short cut for the heat.  It allows the heat to travel up the valve stem faster than if it were solid metal.  The heat still has to travel from the sodium through the outer metal of the valve stem, but the sodium gives it a short cut from the valve head to the end of the stem.

JMO,

paulie

[Heo]

Heat dissapation.  Spelling??

Think about it like the insulation in a wall in a house. but the other way around
The insulation is there trapped all around to stop heat transfer
Insulations heat transfer= Low
Sodium heat transfer= high

And like this to change the state of the sodium from solid to liquid form it
takes energi (heat) Like with transforming ice to water

[plovett]

And like this to change the state of the sodium from solid to liquid form it
takes energi (heat) Like with transforming ice to water

I think the phase change occurs as soon as the engine is warm.  Sodium goes from a solid to a liquid at around 98C or around 208F.

So I think once an engine is up to operating temperature the exhaust valves are going to stay above that temp.  So no phase change inside the valve stem in the running (and warmed up) engine.  I could be wrong about that though.

paulie

[TorinoBP88]

Here is a video of sodium explosion in water !

https://www.youtube.com/watch?v=FK-HA_5mAAI

[Heo]

I remember we had it at school in the cemistry lab
it was stored in kerosene
Some one stole some of it, and we take it down
to the river and filled a coffe can with water and
dumped the sodium in the can and nothing hapened
This was late autum and almost freezing temp
Some genius said lets piss in the can so it gets warmer
He started to piss and seconds later it exploded
Hes running around screaming I got piss in my mouth Igot piss in my mouth
 

[66FAIRLANE]

Great story, had me laughing. At least it was his own piss!

So it was to conduct heat away from the head and into the stems faster........hmmmmmmmm.

[ScotiaFE]

In light of the engine failure i had on Sunday, dropped an exhaust valve from a used set of CJ C8OE heads (unknown valves at this point) and beat up my 'new' 416 bottom end (link to story at: ( http://www.network54.com/Forum/74182/thread/1458099200/last-1458162466/View+Thread )),

My question is one that has been asked a dozen times before (but my perspective is different now!):

1) Do i rebuild these CJ heads (or a set of C6AE-R heads) with all new parts new guides and exhaust seats at least,

or

2) Do i buy a set of Edelbrock heads (or save up a little more) and get Survival or BT heads.

Some pretty good deals on BBM's right now.

[ChiefDanGeorge]

If you're an Amazon Prime member, get the Amazon Store Card. I got a set of Edlebroks and used the finance interest free for 12 months with the Amazon Card.

[Joe-JDC]

Two things about the sodium exhaust valves.  The valve is much lighter from being hollow, and the sodium turns to a liquid at body temperature.  It pulls heat away from the valve head faster, and being lighter, only needs 90-110# seat pressures to keep from bouncing off the seats at high rpm.  Less weight, less spring pressures, equals more horsepower available from same camshaft profile.  Joe-JDC

[427Fastback]

Pretty sure the exhaust valves in my 39 Dodge were sodium filled and I wouldn't be surprised if the Hercules engine for the Diamond T had them as well..Were talking low reving,light spring pressure flats heads tho...

[machoneman]

I do remember reading that hollow stemmed valves were first used in pre-WW1 (no typo!) and WWI radial air cooled engines for all the reasons mentioned, plus one. In heavy use, apparently the stems would grow laterally enough to seize the valve in the guide and kill a cylinder. Not a good idea when your at 7,000 feet! Once warmed up, the valve heat at the stem would stabilize, hence no more seizing.   

This source says 1919 but I'm sure engine before then had them as well.

http://www.aucountry.com/ACA_Folder/Technical/Valves.html

Btw, most light-medium aircraft engines like Lycoming still use sodium valves to this day.