no oil pressure

by Andy LaVasser in General Tech Discussion 6 years ago

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Re: no oil pressure

by Rob Seaton » 6 years ago

Rob Seaton

3 1.32k 240

Roger is correct: The oil purge must be done as per the Installation Manual or SI-912-018

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Re: no oil pressure

by James Stroud » 6 years ago

James Stroud

1 8 0

I understand Bill's reply and thanks Bill for tip on how to pressurize the crankcase. The question that I have is: Using the starter or hand spinning the prop, the blow by to the crankcase is reduced with the upper plugs removed. Why is spinning the prop with the starter incorrect and hand propping is correct.

Even with the upper plugs removed there still will be some blow by. Spinning the prop with the starter will have much more blow by than spinning by hand.

When I change the oil in my 914 I use the starter to fill the oil filter and oil lines. When I finish there is always oil in the tank. I understand that it will take longer to purge the oil lines than to change the oil.

Thanks Bill, Roger and Rob for all of your help in this forum.

Jim

Thank you said by: Kevin Machniak

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Re: no oil pressure

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.97k

With the plugs (Upper or Lower) out there will be NO Blow-By.
It is not a matter of reduced Blow=By. it is Zero Blow-By.
Each cylinder has two plugs.
Remove either one of them, and there will be NO compression.
Without compression. Oil is not going to be returned to the Oil tank.

When cranking with the starter, The engine is turning at a higher speed.
The Oil pump is a Positive Displacement Pump and pumps the same amount of oil per revolution no matter what the speed.
If the engine is not actually running, the pressure in the cylinders is greatly less than when the fuel is being burned. Blow-By is minimal.
This means that the amount of Blow-By is greatly reduced when manually (Electric or Hand) turning the prop as compared to when the engine is firing.

When hand turning the prop, you are instructed to stop at the peak of each compression stroke to allow the greatest amount of Blow-By to occur.
When turning the prop with the starter, the engine quickly passes through the high compression portion of the stroke and Blow-By is minimal at the same time the Oil flow is maximized by the higher cranking speed.

Electric cranking is the worst of both worlds. Max Oil, Min Pressure.

If you want to crank the engine (Ignition OFF) with the starter for a few seconds to confirm Oil pressure; that will not cause any undue problems. Just don't keep cranking it for an extended period without realizing that you may need to "Burp" the crankcase to return any excess oil back to the Tank.

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

Thank you said by: Ken Ryan, Frank Kebe

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