ROTAX Service Instruction: Introduction of Sodium-Filled Exhaust Valves and New Cylinder Heads for ROTAX® Aircraft Engine Types 912 and 912 i (Series)

Hi Christopher,

Yes, you are correct. You have the updated cylinder heads with the upgraded valve seats, but you do not have the sodium-filled valves.

As mentioned above, Rotax will be discontinuing the older valves and cylinder heads. If you ever need replacements in the future, you will automatically receive the updated components.

This upgrade is not mandatory or required but rather an overall improvement to the product.

Thank you RO,

From your explanation, my understanding, this is a manufacturing efficiency/consolidation decision, by Rotax,  that may affect my engine sometime in its future service life, should it need either replacement valves or cylinder head.

There is no operational benefit to my engine, the changes being to parts design & standards.😈

Sean,
I don’t know about you, but if I was having my engine overhauled and it needed one new head, it would be hard for me to use just one of the new type and three of the old. So I guess for retentive folks, this could lead to an expensive upgrade at TBO.  

Hi all

With the introduction of the 912iS engine Rotax produced a new head design with improved cooling.  (lower volume heads that improved flow)  Within 2 years of that introduction they made changes in production and all the 9 series engines got the new heads.  The iS have different part numbers due to some slight variations on the intake, one with O rings and the other, iS, with gaskets to keep the injectors from too much heat transfer.  The valves and seats were the same as the older heads.  The major difference for using them in an older engine was the cylinder temp sender in the old head was into a dry hole and measured material temperature. (CHT)  The newer design used the same sensor but it was moved from a dry hole to a new position and into the coolant, There was a slight change in the temperature readings and if you changed heads you had to make sure that your instrument and POH reflected the new values and the operator knew it was measuring coolant and not head material temperature.  This was explained in Service Information releases at the time.  (vintage 2012 to 2014)

In 2017 Rotax started on the type 915, a turbo engine with much higher heat production.  At that time Rotax introduced the sodium valve on the exhaust.  This same valve was also introduced to the type 914 to add some protection from the turbo heat.  In the 915 they matched this by also adding a new exhaust valve seat to better cool the valve.  With the introduction of the 916 this had the same head and valve with valve seat combination and it was recognised that only valve lapping should be done, no seat rework is allowed for that new seat.  Given the volume of heads and valves Rotax made the decision to standardize the Sodium valve with the new exhaust seats into all the production to simplify parts with less parts variation.  

As you have noted interchangeability is allowed.  If you reach TBO, the point where you would replace the exhaust valves normally, Rotax will supply the sodium ones.  New heads with the newest part numbers will have the harder valve seats.  

Cheers