Oil level

by Jacques Foucher in 912 / 914 Technical Questions 8 years ago

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Re: Oil level

by Roger Lee » 8 years ago

Roger Lee

127 5.2k 4.78k

You actually have three types of valves so to speak. This is what makes the Rotax filter so unique and different from most auto filters and why you should just use the Rotax filter. One is the white anti drain back valve membrane that covers the small holes around the base. This was changed years ago too to make it more effective. Another is the bypass pressure diiferentail spring type on top of the filter and this is for the clogged filter bypass. Most auto filters bypass between 13-15 psi and I believe the Rotax filter bypasses between 18-22 psi. If this was ever actually activated you're way past a serious problem. Rotax years ago increased this spring bypass pressure because sometimes on a cold start the spring could open and allow so unfiltered oil to pass. If you are using a cheaper oil filter or auto filter you are most likely bypassing unfiltered oil at times during a start. For this bypass to work there must be a differential pressure between the upstream oil flow and the downstream oil flow. The last is the internal check valve that you can see looking into the filer. This helps stop oil filter drain that might cause oil to seep into the cylinders. The oil tank has a specific height relationship to be mounted with the engine. Aircraft like Kitfox mounted the tank too high which would cause oil to weep back towards the cylinders which in the early days could cause hydro lock.

p.s.
Don't use cheaper oil filters trying to save $5. Pay now or pay later and later may be a whole lot more expensive.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Guilherme Tomazini

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Re: Oil level

by Jacques Foucher » 8 years ago

Jacques Foucher

19 107 246

Thank you for these good explanation Roger!

No problem, I use only original parts Rotax
no problem and tranquility costs 5 € more , it's not very expensive ! :P

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Re: Oil level

by Jacques Foucher » 8 years ago

Jacques Foucher

19 107 246

I will try to get closer to the ideal position described in the installation manual (see red marks on the drawing)
I just thought save working time by not moving the tank ... :evil:

Oiltankposition.jpg (You do not have access to download this file.)

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Re: Oil level

by Bill Hertzel » 8 years ago

Bill Hertzel

13 1.95k 7.97k

For the benefit of other readers that might be thinking that purging the oil in the crankcase with the starter and the Ignition OFF might be a lazy man's version of hand cranking, consider this.

The oil pump is a positive displacement pump. It pumps a specific amount of oil for each revolution. No matter what!

With the engine running, a considerable amount of the oil is bypassed back to the oil pump input by the pressure regulator. Only the amount of oil that is needed by the engine continues on to the oil galleries.
The pressure bypassed through the piston rings is more than enough to return the oil in the crankcase back to the Oil Tank in a timely manner.

With the engine stopped and hand cranking the prop and stopping at the top of each compression stroke, The minimal amount of oil is going to be pumped into the engine and the full displacement of the cylinders is going to bypass the piston rings, returning the maximum amount of oil back to the Oil Tank.

With the engine being cranked by the starter, due to the slow rpm's, The minimal amount of oil is going to be bypassed with the majority going into the engine. This is great for starting, but bad for purging. Additionally, without the ignition firing, the cylinder pressures are going to be minimal. And without the top of compression pause, The amount of gasses bypassing the piston rings will be minimal.
This becomes a case of pumping the most Oil and returning the least. You might see the level in the Oil tank get lower instead of filling.

Hand cranking with the oil tank cap removed and pausing at the peak of compression while listening for the oil tank to "Burp" is the way to go!

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

Thank you said by: Rob Seaton

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Oil level

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