Prime oil system ?

[procharger]

What the best way to reprime oil system after hose change??

[Jacques]

the Rotax way

https://legacy.rotaxowner.com/si_tb_info/serviceinfo/si-912-018-r3.pdf

 

[procharger]

On 912 just pressure through nipple and turn prop until I get

pressure on gauge check rocker arms after run. Service

instruction mentions 915 914 and two lines.

[procharger]

I primed system today using some air pressure after several turns

of prop I saw 40 lbs on gauge turning by hand.

[Anticept]

I've been able to prime the system just by rotating the prop, but I can tell you you'll be there for half an hour turning it unless you take out a plug from each cylinder and spin until you get a good pressure rise on the gauge (takes a couple minutes). Just because you start to see a pressure rise doesn't mean it's fully primed yet though, keep spinning for a bit, and now you gotta put the plugs back in, spin some more, and make sure you start getting oil flowing back to the oil reservoir.

If you spin it without putting the plugs in to check for oil flow back to the reservoir, you'll draw down the reservoir and it will just sit in the bottom of the case. Remember: the oil return is powered by crank case pressure from piston blowby.

Trust me, it's easier to just put air pressure on the reservoir like rotax recommends and force the oil to start!

[procharger]

I pulled valve covers and checked lifters and valve clearance like rotax

said to do. All is good several runs since I did it.

[airhound]

I’ve done both methods; turn prop until arms fall off and apply air pressure to the oil sump and turn only til one arm falls limp.  The later is better for me, however I fought air leakage around the tank lid even with a tight band. Air leakage such that my small air compressor was maxed out trying to maintain whatever pressure the book calls for. I think 10 psi. Is that normal, or do I need a stronger compressor, or?

[Roger Lee]

The easy way is to remove the top plugs. Makes it easy to turn. Put 5-15 psi onto the tank ( I use 10) via the small vent tube fitting on the neck of the tank. Remove the "In" hose fitting, but don't let it hang down or you'll drain out the oil in the bottom of the engine. I put a rubber cork in it  until I need it out. You will hear air coming out from under the oil tank cap. That is normal and it was never meant to be a pressure tight cap. The regulator on the compressor will keep the air supply at 10 psi. I now put on a pair of leather welders gloves to protect and pad my hands. When I apply the air I let the hose off the bottom of the engine hang down to my catch tub. Then I spin the prop at about 1 rotation or more per second for about 80 turns. Then I stop for a moment and turn the air off. Take 3 minutes and then apply the air again and do another set of rotations for a minute. If you turn on the instruments I generate about 50-55 psi oil pressure. I like to do the purge two times. I'm a little anal and never want an engine mishap. In 20 years of doing it this way I have never had an instance where the valves were soft or where there was ever an issue. At startup I usually have instant 60+ psi oil pressure.

All the air pressure does in the tank is put pressure on top of the oil to push it through the oil cooler and into the oil pump inlet. After that the pump is positive displacement pump and doesn't need the air past that point. I just needs the air pressure to feed it the oil.

Leaving all plugs in will work, but what a PITA to turn and do a good job and you never know for sure if the oil was pressured in all the right places. That's why you need to check for soft valves. I've never had or seen a soft valve my way and maybe because I do it twice.

[MileHighCTLS]

I watched the Rotax Owner's Website video on purging the oil system and it left me with one big gaping question: What do you do if you have the optional thermostat?

With the optional thermostat (as in my engine), the entire oil cooler circuit is bypassed when the oil is cool. Conversely, it only circulates the oil thru the cooler when the oil is hot. The video it says that these systems need special attention to be sure all lines are purged of of air.

Mmmmm, since I will be purging the system when the oil is cool, by my calculation, the entire oil cooler circuit will not be purged. 

Any thoughts on this?

[Anticept]

The oil thermostat never fully closes.

[Tom Baker]

What Corey said. You can also pre fill the cooler before you attach the hoses.

The pressure purge is designed to get air out of the oil system, because the Rotax engine doesn't do a good job of self purging air from its lifters. Air in the lifters causes damage to the valves, which in turn causes valve failures. The most important part of the pressure purge procedure is checking the lifters after your initial test run of the engine. If the lifters are solid, you will not have any issues. If you have one that is soft, re-purge, run it, and check again like they spell out in the instructions.