Oil (air) purging procedure for 912

[AeroDog]

According to Rotax, before first engine start the oil is forced into the various passage ways and air purged from the lifters by rotating the prop 40-60 times (less if tank is pressurized with air). The inlet line to the tank is to be removed and oil which would have gone into the tank is collected in a clean container. After seeing 40 psi on the gage, the oil line is re-connected to the tank and the collected oil is filtered back into the tank. My question is this: Why collect the oil and then put it back? Why not let the oil discharge back into the tank the way it normally does?

Jerre

 

[Eriselle]

Referring to the 912iS Installation Manual section 79-00-00 Page 21-22, I do not see any step where the oil in the container is returned to the oil tank. Step 11 mentions returning oil in the crankcase to the oil tank (i.e. a standard burping procedure). My interpretation of these instructions is that the oil that enters the container during this procedure is waste oil.

The aforementioned pages in the installation manual refer also to SI-912 i-004 which mentions this:

NOTE: This step is a cleanliness precaution. Typically, during the purging procedure,
oil does not come out from the hoses.

Once again, the similar instructions in the Service Instruction do not mention returning the oil from the container to the oil tank.

 

[Tony_T]

According to Rotax, before first engine start the oil is forced into the various passage ways and air purged from the lifters by rotating the prop 40-60 times (less if tank is pressurized with air). The inlet line to the tank is to be removed and oil which would have gone into the tank is collected in a clean container. After seeing 40 psi on the gage, the oil line is re-connected to the tank and the collected oil is filtered back into the tank. My question is this: Why collect the oil and then put it back? Why not let the oil discharge back into the tank the way it normally does?

Jerre

Jerre
The procedure is to turn the prop quickly with the spark plugs out. This engine is designed to pressurize the crankcase by piston ring blow by. The engine will not return the oil to the tank because there would be no pressure in the crankcase with the plugs removed.

 

[AeroDog]

Referring to the 912iS Installation Manual section 79-00-00 Page 21-22, I do not see any step where the oil in the container is returned to the oil tank. Step 11 mentions returning oil in the crankcase to the oil tank (i.e. a standard burping procedure). My interpretation of these instructions is that the oil that enters the container during this procedure is waste oil.

The aforementioned pages in the installation manual refer also to SI-912 i-004 which mentions this:

Once again, the similar instructions in the Service Instruction do not mention returning the oil from the container to the oil tank.

In Rotax Tech Tips #15 (YouTube) he says you may return the oil to the tank (filtered). I like what you say better. Thanks.

 

[AeroDog]

Jerre
The procedure is to turn the prop quickly with the spark plugs out. This engine is designed to pressurize the crankcase by piston ring blow by. The engine will not return the oil to the tank because there would be no pressure in the crankcase with the plugs removed.

Ah ha! Makes sense. Thanks.