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[dlaws01]

I was just wondering if using sodium filled exhaust valves with better, larger oil cooling capabilities around the exhaust valve in the heads had ever been considered by the MOCO.  I have seen it applied to air cooled cylinders on aircraft with decent success.  For a relatively low RPM engine it seems to be a viable solution.   

[Phantom309]

What purpose does filling them with sodium supposed to do? Help dissipate heat? I always thought sodium/salt is a corrosive ... why put it inside any type of metal? Doesn't sound like a good idea to me.

[Chains]

The reason for sodium filled valves is for heat dissipation as I remember.

[FLTRI]

I was just wondering if using sodium filled exhaust valves with better, larger oil cooling capabilities around the exhaust valve in the heads had ever been considered by the MOCO.  I have seen it applied to air cooled cylinders on aircraft with decent success.  For a relatively low RPM engine it seems to be a viable solution.   

I hope we find out why the MOCO chose water over oil since they had success with the cooling on the XR1200...I believe.
Maybe water is more efficient?
Bob

[Thermodyne]

Oil conducts heat poorly.  Water based coolant conduct heat very well.  Water radiators are much less expensive than oil radiators.  And if you actually got oil close enough to the valve seat for it to be effective, coking would become an issue.

As for sodium, it acts as a heat pipe.  Moving heat away from the valve head and into the upper stem, where it can transfer to the guide.  It was originally used to stop valve heads from burning.  Now, stainless steel does the same thing for less cost.  Sodium filled valves are also hazardous, sodium and water don't mix well.  Old time machinists hated them, grinding into the sodium by accident, or creating a crack made for a real moment when the water based grinding coolant hit the sodium.  I don't think you'll ever see them in a mass produced engine again.

[North Georgia Hawg]

I hope we find out why the MOCO chose water over oil since they had success with the cooling on the XR1200...I believe.
Maybe water is more efficient?
Bob

OK... I'll take a swing at this...

Water is more dense than oil, and is also of lower viscosity. A volume of water can absorb more heat than an equivalent volume of oil. Motor oil can absorb around 75% of the heat as an equivalent volume of water.

However, the coolant is about 50/50 mix of ethylene glycol and water, most likely. Ethylene glycol can absorb about half the heat as an equivalent volume of water ... so, a 50/50 mix of ethylene glycol and water can absorb 75% of the heat as an equivalent volume of water.

So... motor oil can absorb about 75% of the heat as water, and the 50/50 mix of water and ethylene glycol can also absorb that same, or a very similar, 75% as water.

Therefore, ethylene glycol/water cooling is really not any more efficient from that perspective. But, ethylene glycol/water has a lower viscosity than motor oil... thus, it can shed that absorbed heat more quickly in a radiator than motor oil can.

SO... I suspect that the MoCo probably found that using ethylene glycol/water as coolant is more effective than is using motor oil as a coolant. After all, autos use it, and not oil. This is a very rough and incomplete analysis... but that's essentially why I think they went with the ethylene glycol/water as a coolant, rather than oil. It can shed heat more quickly because it's thinner than oil.

Plus, I highly doubt they could have gotten away with having very hot motor oil sloshing around at pressure in the lowers. That could be VERY hazardous in a crash! And no one has been able to engineer a giant oil cooler with enough capacity to cool a big 1803 cc engine any other way yet, and make it physically not take over the entire front end of the bike, and thus not entirely ruin the Harley look we all love!

What I have said above may all be dismissed as total crap by a real expert in thermodynamics, but I think it's basically the rough truth... ethylene glycol/water cooling simply works better then pure oil cooling because it can absorb and shed heat more rapidly.

OK... I'm ready for the spitballs now!

Ken

[dlaws01]

Oil conducts heat poorly.  Water based coolant conduct heat very well.  Water radiators are much less expensive than oil radiators.  And if you actually got oil close enough to the valve seat for it to be effective, coking would become an issue.

As for sodium, it acts as a heat pipe.  Moving heat away from the valve head and into the upper stem, where it can transfer to the guide.  It was originally used to stop valve heads from burning.  Now, stainless steel does the same thing for less cost.  Sodium filled valves are also hazardous, sodium and water don't mix well.  Old time machinists hated them, grinding into the sodium by accident, or creating a crack made for a real moment when the water based grinding coolant hit the sodium.  I don't think you'll ever see them in a mass produced engine again.

The idea is that the sodium filled exhaust valves would be used in conjunction with a head that has more efficient oil flow around the valve guide.  The sodium to remove more heat from around the valve head and higher oil flow around the guide to reduce the heat transferred there via the valve stem. Sodium filled valves have a hollow head and stem filled about 60% with Sodium. Sodium has an extremely low melting point (about 100 degrees C) and boiling point (880 C).  The valves are hot enough that the sodium in the head of the valve vaporizes and travels up to the cooler stem where it condenses back to a liquid again. The phase transition from liquid to gas absorbs a lot of heat, and the condensation dumps the heat into the stem where the large metal-to-metal contact between the valve stem and guide transfers that heat to the more efficient, higher volume oil passages in the heads. Without this heat pipe effect, vastly more heat would have to be transferred through the valve seat. Too much heat through the valve seat, and you get a burned valve.  Even experimenting with valve seat angle to minimize heat buildup thus transferring more heat through the sodium valve stem, into the guide then into the cooling oil.  Again under relatively low rpm operations on an air cooled engine that has a history of heat issues I believe it would be worth a R & D prototype, at least. I guess we will never know.