Rotax Discussion


I attended the 7/28/04 8:30am "Rotax 912 and 912S Basic Engine Maintenance" forum. Here are the notes I took from the session.

Eric Tucker, works for Kodiak Research, the Rotax Importer for the US. They sell engines to Lockwood Aviation Supply, California Power Systems etc. Eric was shown as the presenter in the program, but in fact he was backup for Phil Lockwood.

Phil Lockwood did most of the presentation. He is the owner/manager of Lockwood

Aviation Supply.

The presentation applied to all Rotax four stroke engines. 912, 912S, 914, certified and non certified versions. I'll use 91x to indicate all these engines in the following notes.

Through out the presentation, both Phil and Eric stressed that the 91x family of engines, once running, will get you to your destination. They may self destruct in the process. Loss of all the coolant will result in overheating; engine would keep running, but will likely warp the heads. They implied the engines would run without oil for a long time - again, the engine may not restart after this abuse. I believe there were other examples that I did not write down.


Oil discussion:

- Recommend maximum 50 hour oil change. This is more frequent than the manual states for some conditions.

- Pre-oil the new oil filter when doing an oil change. (That is fill the filter with new oil before installing it on the engine. Some discussion about mess followed, and Eric said to at least fill the new filter half way with oil, then it could be installed without pouring the oil out.)

- When installing the filter, max three quarter turn after rubber gasket makes contact with the engine case. DO NOT turn filter until the filter touches the case.

- Oil formulations have been changing during the last several years. The newer oils foam more. This can cause problems in the 91x family.

- The oil dipstick change was because of the foaming.

- Recommend keeping the oil tank near the top of the range.

- Proper way to check oil is to rotate the prop in the normal direction until the oil tank gurgles. Then check the level in the tank.

- DO NOT rotate the prop backwards. This can pull oil out of the engine. A few degrees of backward rotation is not a problem. A full rotation of the prop could be a problem.

- When changing the oil, just remove the oil tank drain plug to empty the oil tank and change the oil filter. DO NOT try to get ALL the oil out. Some customers who have had oil related problems have rotated the prop backwards to pump the oil out of the engine during their oil changes.

- Need to use motorcycle type oil because the 91x family shares the crankcase oil with the gearbox oil - like most motorcycles. This oil has additives to protect the gears.

- Castrol GPS and Motul have been REMOVED from the recommend list because of foaming.

- Penzoil motorcycle oil is OK to use

- Any semi synthetic motorcycle oil is OK to use.

- Honda motorcycle oil will not be listed as OK to use because Honda is possible competitor, but the Honda motorcycle oil is OK to use.

- California Power Systems AV-9 showed some foaming in testing and is currently being reformulated.

- DO NOT use pure synthetic oil when using 100LL fuel. Pure synthetic will not hold the lead in suspension properly.


Cooling discussion:

- Recommend CHT operation in 180F to 240F range. Also recommend max of 125C which is higher than 240F.

- It is normal for EGT and CHT to be different on each side.

- No real value to having EGT.

- IF the center of the CHT sensors supplied with the engine are gone, then the engine has been TOO HOT. The center of the sensor has melted.

- There is a new higher pressure radiator cap available. Eric did not seem to enthusiastic about it. Typically raises the temperature before releasing pressure about 10C.

- Use phosphate free coolant.

- Use silicate free coolant.

- Dexcool coolant works well.

- Don't mix green and orange coolant. Flush system if changing.

- Recommended minimum of 50% coolant (with remainder being distilled water).

- If having trouble with coolant/distilled water boiling, may need to move to highest recommend concentration of coolant as recommended by coolant manufacture.

- If still having trouble with coolant/distilled water boiling, using Evans coolant is OK. Evans coolant does not use water and runs without a pressurized cap.



- If flying over 12,000ft, recommended using avgas to avoid vapor locking.


- Keep the carbs synchronized. Check every 100 hours. Check at idle and just off idle.

- Recommend 1800 rpm as minimum idle speed to maximize gearbox life.

- Recommend overhauling the carbs every 600 hours.

- Choke (enricher) only works with the throttle fully closed.

- Recommended running 2200-2400 RPM just after start until engine will idle smoothly below this speed.


Gearbox discussion:

- Recommend 912S engines be upgraded to the slipper clutch. There is increased possibility of kickback with the slipper clutch. Therefore, this also requires the upgraded starter at the same time. There is a reduced cost upgrade program available.

- Recommended having gear box serviced every 300 hours of operation for 912S without the slipper clutch (over run clutch).

- There was a recommendation to check the gearbox play every 100 (?) hours of operation. The discussion followed what is in the manual. This is for engines which do not have the slipper clutch. Sorry, I'm not sure of the frequency that was recommended.

- Would not try to hand prop a Rotax 912S. Much higher compression than the 912 or the 914.


There was a discussion about the service bulletins. Basically, there are bulletins because the factory continues to develop the engines. The development is the result of customer/user feedback. Service bulletins are only required for certified versions of the engines in certified planes. The service bulletins are a good idea for the non certified engines.


I hope some of you find this posting useful.




N601RT: CH601HDS, nose gear, Rotax 912ULS, All electric, IFR equipped, 270hrs, 338 landings