Thursday, June 30, 2016

Performing Oil Purge Process On The Rotax 912ULS Engine

Prior to starting the Rotax 912ULS engine for the first time or anytime the supply oil line is removed between the oil tank, oil cooler or Rotax 912ULS engine an oil purging procedure MUST to be followed to remove air from the oil system.

The procedure is not complicated, but does require help. In a nut shell, the goal is to pressurize the oil tank to between 6 and 14 psi of pressure and with the sparkplugs removed from the cylinders, spin the propeller as fast as possible by hand for a minute or two allowing the hoses, oil cooler, and internal oil galleries to completely fill with oil until a steady oil pressure is built up.

The setup: To perform the oil purge, the oil return line from the engine is removed from the In port on the oil tank ... and the In port on the oil tank is capped off. The oil return line is to be placed into a container to capture oil … I elected to just use a vinyl hose directly off the fitting on the crankcase to collect the return oil. The oil tank is pressurized via removing the air vent hose and connecting an air hose to the air vent fitting on the oil tank. I made up a small manifold so an air gun could be connected to a pressure gauge via 1/4" tubing. From the manifold to the oil tank 3/8" ID tubing is used.
An air gun connected to a manifold with an air gauge is used to control the amount of pressure applied to the oil tank. A 1/4" ID hose connects the air gun to the manifold and a 3/8" ID hose connects the manifold to the air vent pipe on the oil tank.

As mentioned previously, I elected to connect a vinyl hose directly to the oil return fitting on the bottom of the crankcase instead of dealing with collecting oil dripping out of a hose on the top of the engine. The vinyl hose created a small issue in that it wanted to kink because the muffler is so close to the return oil fitting on the crankcase the vinyl hose needed to make an abrupt bend. To solve that issue, a piece of stiff safety wire was curled up and inserted into the hose to prevent it from kinking.
To collect the oil that will run out of the oil return port on the bottom of the engine during the oil purging process, a vinyl hose was slipped over the fitting. A piece of safety wire was curled up and slid inside the soft vinyl hose to prevent it from kinking at the bend.

With all systems a go, the manifold assembly was connected to the air vent on the oil tank and the regulator on the air compressor was backed down a bit so Mike K. could easily control the air flow to keep a steady 10 psi of pressure applied to the oil tank. Because the oil pressure sending unit was moved from the engine and mounted on the firewall, figured it would be a good idea to first make sure the hose was full of oil … so the fitting was removed from the oil sending unit (I had never tightened it knowing it would be removed for the purge) and while Bernie held the oil sender  line in a rag, the prop was vigorously turned until oil flowed from the hose. This took a little while because there is a restrictor on this oil line at the engine. Once the line was full of oil it was connected to the oil pressure sending unit and the official purge process began. (Note: Builders who do not move the oil pressure sender to the firewall would not need to fuss with this first step).
Mike K. the “pressure man” controlled the air pressure being applied to the oil tank's vent fitting, keeping it around 10 psi during the purging process. During the oil purge process, the oil return hose is removed from the oil tank and the In port on the oil tank is capped off ... which can be seen in this photo as a blue cap on the In port on the oil tank.
Oil running out of the oil return fitting on the bottom of the crankcase was collected in a clean container and poured back into the oil tank through a paint strainer when the purging was completed.

By the time oil began coming out of the oil pressure sender line I was getting a little tired but after connecting the oil line back on the sender unit continued to spin the propeller until oil began flowing out of the oil return port on the bottom of the crankcase. This is when we switched roles and I turned on the Skyview to monitor the oil pressure, Mike began turning the propeller, and Bernie controlled the air pressure applied to the oil tank. After a few moments the oil pressure came right up and Mike had it holding steady at 78 PSI and the pressure would vary depending on how fast or slow Mike turned the propeller. With the oil purge complete. there is one more step that is required before an engine start is attempted and that is involves removing the rocker arm covers and verifying all the hydraulic valve lifters are pumped up … this will be covered in the next post.

This concludes the oil purging process … we return to normal programing.