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Re: [T3] Stretching valve stems?

On 15 Nov 2005 at 12:20, Dave Hall wrote:

> There were 9mm sodium-filled valve stems in some 1600cc VW campers - not sure
> what others.  I imagine a hollow empty stem would not transfer heat as easily as
> you'd want.   Does the sodium fill it completely?

I never heard of VW 1600s with sodium valves, although later type 4 engines 
came with them and those were certainly used on buses. I've heard that late 
Beetle FI exhaust valves had 9mm stems, but I've never seen any of those. The 
1600 was sold in buses in Europe long after it was replaced by the type 4 
engine here, so I suppose some of those engines might have gotten sodium valves 
about the same time that the type 4 engines did. None of my manuals discuss 
those vehicles, however. I should see if I have VW microfilm on them.  

I agree that a hollow empty stem seems like a heat transfer problem.

The sodium valves are mostly empty, with just a bit of solid sodium in them. At 
operating temps, the sodium boils and carries heat very effectively to the top 
(stem end) of the valve, where it condenses. It then runs back down to the head 
end by gravity and the shaking of the valve. It's my understanding that they 
will actually work in any orientation, but I can't help feeling that they must 
be much more effective if the head end is lower than the stem end, as they are 
in VW engines.

Jim Adney
Madison, WI 53711-3054

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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