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Rotax 912 Lubricant / Oil Purging

richpezz

Member
This is my first experience purging my new Rotax 912is prior to first engine start.

I’ve purged the system twice by hand propping and using compressed air in the oil can. After approximately 60 prop rotations I could only achieve 10psi on my Dynon panel, far short of the 20-40psi Rotax calls out in their video. The Rotax Service Instruction states you need “indicated” pressure, not a specific psi.

Can anyone shed light on this process as I want to make sure I get this right?

Thanks

Rich
 
If you achieve a pressure indication on the EFIS when turning engine by hand, then air is purged and oil galleries are filled with oil. Engine start will develop oil pressure within 10 seconds.
 
I agree with Jim. If you pull the spark plugs and spin th engine with the starter motor you should see a big jump in oil pressure. Just don’t exceed 10 seconds of cranking so you don’t overheat the starter motor.
 
Spinning the motor with the starter with the spark plugs out is not a good idea for two reasons.

Rotax depends on pressure in the crankcase to push oil back into the tank. With the plugs out, there will be no pressure and you risk having all your oil in the crankcase and none in the tank so the system loses prime again.

Be certain the spark plugs are grounded (jumper from the threads to the engine case) if you do try this, otherwise the ignition coils/ modules may be damaged.

Having 10 psi showing should be fine. Watch the oil pressure and start the engine.

Jim Butcher
 
OIL CHANGE - PURGE

I have always used the starter to turn the engine over after oil change. Top plugs out. No stress on engine. I turn it for 5 seconds and make sure the oil level in the tank is going down. ( No air leaks ). Spin with starter until about 56 PSI on display. Pause 30 seconds, then turn for 10 seconds more to verify 56 PSI. I feel it will guarantee the lifters are filled and everything is good. Then put in plugs and burp by hand as usual. You do not have to turn mags on for ANY reason while doing this. I have done it for about 17 years. NEVER a problem.
 
Spinning the motor with the starter with the spark plugs out is not a good idea for two reasons.

Rotax depends on pressure in the crankcase to push oil back into the tank. With the plugs out, there will be no pressure and you risk having all your oil in the crankcase and none in the tank so the system loses prime again.

Be certain the spark plugs are grounded (jumper from the threads to the engine case) if you do try this, otherwise the ignition coils/ modules may be damaged.

Having 10 psi showing should be fine. Watch the oil pressure and start the engine.

Jim Butcher


While it is true that no oil will be returned to the tank from the crank case if cranking with spark plugs removed, only a small amount of oil will land in the crank case in the time that it takes to get oil pressure. So as long as this isn't done for an extended period of time it is an acceptable procedure and we use it in our shop. There is also little chance of over heating the starter motor because the load on the motor is so low because of no cyl. compression.

It is also true that the ignitions should not be firing without being connected to grounded plugs because of the possibility of coil damage. This can easily be dealt with on a 912ULS by assuring that the ignition switches are off.

On a 912 iS it is a little different because the engine can't be cranked with the starter and still have the ignitions disabled. On the iS you can connect the ign. leads to the spark plugs and have the top plugs just laying in the cooling fin recess near the spark plug hole. This will make all 4 plugs grounded and allow the ignition coils to fire normally.
 
Oil Purge

I had to replace the oil pump body because the new style oil pressure sensor is not the 1/8th NPT thread of the older sensor. So purging was required. I tried the hand prop method and could not get the air out of the number four piston lifters. I finally did as explained in this thread and used the starter motor. Air purged on the second try.
 
I'm prepping for my first purge on a 912iS and after reading the Rotax SI and watching their video, I have 2 VERY basic questions:
1) How do I cap the oil tank port after removing the return line? (Where can I get a cap? What threads does it have?)
2) If I turn the engine by hand (bottom plugs out), won't the tank vent prevent any pressure from building up?
 
1) It’s a 1/2” (-8) fitting. You can get an AN929-8D or I used a -8 plastic cap that was used to seal off a fitting on my engine when it was sent.

2) And you’re not using piston blow-by pressure for this task; you’re building up pressure through the oil pump. That’s why all the prop revolutions.
 
2) If I turn the engine by hand (bottom plugs out), won't the tank vent prevent any pressure from building up?
No, because if you do the purge process as directed, you are removing the oil line from the INLET port of the tank and capping it, and then introducing low pressure air via an air hose at the end of the tank vent line (so no air will be coming out of the tank vent.

Doing this will slightly pressurize the oil tank and help force oil through the lines, oil cooler, and oil pump, and help purge all air from this portion of the system. With the engine rotating during this process, the oil pump will be pumping the oil out through all of the internal engine oiling system, with the assistance of the slightly pressurized oil coming into the engine at the oil pump inlet (because of the air pressure induced at the oil tank).
 
No, because if you do the purge process as directed, you are removing the oil line from the INLET port of the tank and capping it, and then introducing low pressure air via an air hose at the end of the tank vent line (so no air will be coming out of the tank vent.

Doing this will slightly pressurize the oil tank and help force oil through the lines, oil cooler, and oil pump, and help purge all air from this portion of the system. With the engine rotating during this process, the oil pump will be pumping the oil out through all of the internal engine oiling system, with the assistance of the slightly pressurized oil coming into the engine at the oil pump inlet (because of the air pressure induced at the oil tank).
Thanks, Scott -- but I'm wondering about the case if I'm not hooked up to 15 psi/1bar pressure into the vent, which Rotax says (in both their SI and video) is optional, and just turning the engine by hand, which they describe as another way to do it. I haven't figured out the collection of fittings & hoses I'd need to get pressure from the air line regulator into the vent opening -- or how to cap the tank inlet. One of your posts on purging mentioned using the starter to turn the engine, with upper plugs removed but attached to their leads so the coils aren't fried - was that in addition to pressurizing the tank?
 
Thanks, Scott -- but I'm wondering about the case if I'm not hooked up to 15 psi/1bar pressure into the vent, which Rotax says (in both their SI and video) is optional, and just turning the engine by hand, which they describe as another way to do it. I haven't figured out the collection of fittings & hoses I'd need to get pressure from the air line regulator into the vent opening -- or how to cap the tank inlet. One of your posts on purging mentioned using the starter to turn the engine, with upper plugs removed but attached to their leads so the coils aren't fried - was that in addition to pressurizing the tank?
Yes, that was in edition to pressurizing the tank.
Are you sure that the service instruction you are referencing isn’t the one for doing an oil change, which just includes turning the prop until getting oil pressure?
If Rotax now says that pressurizing the oil tank is optional, that is something totally new to me, but I haven’t been into the documentation for a couple years, so I guess it’s possible. If it is true, it does surprise me though, because they were so adamant about it previously.
Someone else already listed the AN part number for a cap that you can purchase the cap the open port on the oil tank. The yellow caps that are installed on it when it is shipped also work because the pressure is very low.
I have always used an air nozzle with an extension tube that was a tight fit when inserted into the vent tube. I would first set the pressure regulator for the airline at a very low value around 10 psi, or so, and then, after inserting the air nozzle use aI have always used a air nozzle with an extension tube that was a tight fit when inserted into the vent tube. I would first set the pressure regulator for the airline at a very low value around 10 psi, or so, and then, after inserting the air nozzle, use a small clamp to hold the Valve lever depressed. The cap on the oil tank actually works as a bit of a safety valve because it will begin releasing pressure if the pressure goes above about 15 psi.
 
Typical Rotax, information is a bit of a treasure hunt. The Heavy Maintenance Manual only refers you to the Line Maintenance Manual. The Line Maintenance Manual refers you to the Installation Manual and Service Instruction SI-912-018. The Installation Manual procedure calls for using compressed air but the Service Instruction says compressed air is optional. BTW the Installation Manual also refers you to SI-912-018. Compressed air speeds things along. I've done it with no compressed air IAW SI-912-018 and had satisfactory results. Just a lot of prop turning.
 
Yes, that was in edition to pressurizing the tank.
Are you sure that the service instruction you are referencing isn’t the one for doing an oil change, which just includes turning the prop until getting oil pressure?
If Rotax now says that pressurizing the oil tank is optional, that is something totally new to me, but I haven’t been into the documentation for a couple years, so I guess it’s possible. If it is true, it does surprise me though, because they were so adamant about it previously.
Someone else already listed the AN part number for a cap that you can purchase the cap the open port on the oil tank. The yellow caps that are installed on it when it is shipped also work because the pressure is very low.
I have always used an air nozzle with an extension tube that was a tight fit when inserted into the vent tube. I would first set the pressure regulator for the airline at a very low value around 10 psi, or so, and then, after inserting the air nozzle use aI have always used a air nozzle with an extension tube that was a tight fit when inserted into the vent tube. I would first set the pressure regulator for the airline at a very low value around 10 psi, or so, and then, after inserting the air nozzle, use a small clamp to hold the Valve lever depressed. The cap on the oil tank actually works as a bit of a safety valve because it will begin releasing pressure if the pressure goes above about 15 psi.
Thanks, Scott. I'll pressurize the tank. The Rotax instructions (their video and SI) I referenced were indeed for purging, explicitly saying that air line pressure is optional "but it may take longer without it" -- I'll say. Unfortunately I cleaned up & discarded those nifty yellow caps, so I'll order a screw-on cap.

p.s. don't know if I ever said "Thanks" for your video on the fiberglass lay-up for the RV-10 canopy, which helped a lot when I did that for my 12.
 
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