Service Bulletin: Inspection and maintenance after an overload clutch slipping event on ROTAX® 915 i and 916 i (Series) Aircraft Engines

The significance of oil selection resulting in potential engine and gearbox overhaul requires full transparency which in this case Rotax has willfully disregarded. For complete transparency Rotax should make available all details of the overspeed incidents and oils used. Internal standards are the Fox watching the Henhouse and for transparency needs to certify their oils under ASTM or API standards. In this case those standards for wet clutch performance.

Hi Robert

The issue from Rotax is that there was no exact formulas that were satisfactory from automotive, marine or motorcycle applications.  This gave rise to the Rotax Norm (RON) call outs where they have an internal standard.  It is a bit more complex than a wet clutch in a motorcycle, especially for the type 915 and 916.  The 916 temperature control was a major factor in the development of the XPS oil.  The 916 at 160 HP takeoff power  the Aeroshell Sport Plus 4 was not sufficient.  

They have done releases on the oil that explains this.  Prop mass inertia plays a big role in this as well as the use of inflight adjustable (variable load) props. As an aside the XPS had to also perform with the use of Avgas added into the mix of other factors.  With what I know i would use the XPS on the 915 as well as the 916.  

Cheers

Hi Robert,

Rotax has released a Service Instruction titled: "Selection of Suitable Operating Fluids for ROTAX® Engine Type 916 i (Series), 915 i (Series), 912 i (Series), 912 and 914 (Series)." You can find it here: Rotax Service Bulletins. This document provides a list of fluids, such as engine oils, that have been tested and approved for use in their engines.

The technical content of this document is approved under the authority of DOA ref. EASA.21J.048. In this document, Rotax clearly states, "Only use engine oils tested and released according to the ROTAX® standard (RON 424), see section 3.2." Additionally, "Because of the incorporated friction clutch, oils with friction modifier additives are unsuitable because this could result in clutch slipping during standard operation." Multiple warnings throughout the document state, "Non-compliance with these instructions could result in engine damage, personal injuries, or death."

Similar information is also found in the Rotax operator's manuals. With this said, it's evident that Rotax has been very clear and transparent regarding the engine oils that should be used in Rotax engines.

As for how many issues there have been regarding clutch slippage due to the use of incorrect engine oil, it is clear that Rotax has been made aware of enough of these issues to release a Service Bulletin on the topic.

We are in the process of creating an expanded instructional video that provides an in-depth discussion and information regarding engine oils previously recommended and approved by Rotax, along with the currently approved engine oils. This video will explore the history and reasons why Rotax now only suggests the use of either AeroShell Sport-Plus 4 and XPS engine oil. Engine oil has been a major topic of discussion over the years, and there has been a lot of misinformation surrounding it. Stay tuned and keep an eye out for this video, as we believe it will provide valuable information that will give you a thorough understanding of the subject.

We hope this helps answer your questions, and if you have any further questions or concerns, please don't hesitate to post them in the forum!

As Rotax Owner has stated they have an internal oil standard.  The new XPS oil data sheet, attached, for the 916 is a different standard from the RON 424.  For the XPS it is RON 451.   The data sheet shows what parts are ASTM and API compliant if you are interested. 

Cheers

The issue is wet clutch performance yet Rotax has failed to disclose how this is tested, data generated or what those requirements would be for their engines. In the XPS brochure no wet clutch standards are mentioned. The “Gold Standard” for wet clutch performance is JASO MA or JASO MA2.  ASTM had published a standard for wet clutch performance, ASTM D5005-89, but it was withdrawn in 1995. Without standards and data, what assurances do owners have that either Sport Plus 4 or XPS will prevent overload clutch slippage with these higher torque/horsepower engines?