Question SI-912-038

Yes they can be replaced.

How Does This Affect Me?

If you own, operate, or maintain a ROTAX 912 or 912 i series engine, you'll need to check if your engine's serial number is listed in the service instruction. If your engine's serial number is higher than those detailed in section 1.1, it has already been fitted with the new sodium-filled exhaust valves and cylinder heads and is not impacted by this update. Retrofitting older engines with these new components is NOT mandatory. However, the new sodium-filled exhaust valves and cylinder heads can be installed individually as needed, allowing for flexible integration with existing engine components.

The wording does seem to suggest you can mix old and new components.  I’m curious what the changes are in the new head. Since a sodium filled valve is designed to transfer heat from the valve head up the stem to the valve guide, retainer and spring, it would make sense that a cylinder head designed for these valves could be different. I know one of the issues with sodium filled valves has been increased valve guide wear, the new heads may compensate for the additional transferred heat.  

Please post any questions related to SI-912-038 in the dedicated forum thread we created for this topic. This will help keep all discussions in one place and avoid duplicate posts.

https://www.rotax-owner.com/en/general-tech-discussion/10862-rotax-service-instruction-introduction-of-sodium-filled-exhaust-valves-and-new-cylinder-heads-for-rotax-aircraft-engine-types-912-and-912-i-series

Thanks for your cooperation!