Exhaust Valve Inspection

[facthunter]

It's in liquid form and moves the heat by shaking.   Works much more effectively with larger dimensions. It still ends up going to the valve guide as a heat Path.   Some valve guides in alloy heads are Bronze.. Nev

[facthunter]

Those valves operate in a horizontal position so why would the bulk of the sodium be near the head of the valve?. They will cost a fortune. Time will tell if they are an improvement. By rights the stems should be of a larger diameter. The wall of the stem  is too thin.  With liquid cooled heads, those motors already run cooler than an aircooled motor would . Nev

[Area-51]

Rotax have been using sodium valves since 2018 in all their turbocharged engines, the 914, 915, and 916 all use the same part number. Besides an AD requiring replacement on one manufactured batch I have not seen any reports regarding either valve or valve guide failure with their sodium valves; and there are sure to be TBO'd engines running on condition by now in the field.

 

The factory change to sodium was due to more extreme combustion environment in the turbo charged engines, i.e. heat affected deterioration. A 914 with an intercooler might negate this however the 915 and 916 probably not.

[Area-51]

After realising yesterday the valve head crazing was deposition, out of interest today I took to some old skills and decided to see if the deposition could be removed.

 

[facthunter]

Most engines have larger dia exhaust stems on the exhaust valves to help move the Heat. Anyone can see the weakening of the present valve stem and I'm not convinced the Sodium would make that much difference. The valve seat is the Path most heat will pass through. What price is on them? Nev

[facthunter]

It did look metallic and I doubt it's due to lead... What's your thoughts after removing it?  It could be from an aluminium shaving/burr from some where upstream in the inlet  or turbo. Nev

[Area-51]

The turbo unit is in as new condition and free of compressor binding... If I knew these engines as well as I know others I would now use them without concern. But I don't have enough time on these things to know their practical limitations. Will still put set of standard valves in to tick the box; about $550 a valve. The engine is being built for reliability and distance work. Old ones can get polished and put into a lesser 80hp scavenger rebuild test pig unit. 

[facthunter]

If it's any help to you I've seen aluminium produce just what you appear to have. Bits hang about in the combustion chamber and don't easily exit the exhaust port as you might intuitively expect it to. I  won't post any more on this unless you ask.    Nev

[Area-51]

Thanks, will do some research on that one... I think we are done here on this. thanks for everyone's input; some useful applied knowledge to refer to...