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  #1  
Old 09-02-2017, 01:23 PM
jnmeade jnmeade is offline
 
Join Date: Mar 2013
Location: Iowa
Posts: 135
Default Why Burp Rotax 912ULS?

We've all been taught to "burp" the Rotax 912ULS to move the oil from the crankcase to the oil tank so that we can accurately measure the oil level. Here is a nice technical discussion of what happens.

https://electricmotorglider.com/2017...otor+Glider%29

In addition to moving the oil from the crankcase to the oil tank, some hold that "burping" enough blades also tests for hydrolock. Hydrolock seems to be a phenomenon that is very rare in a flat, opposed engine. I've never been taught or seen any emphasis on testing for hydrolock in a Continental, Lycoming, Franklin or any other flat engine I've flown, so I'm going to assume that testing for hydrolock is not a necessary reason to "burp" a Rotax 912ULS. If that is in error, please give me the reference so I can learn.

When we fly an IO360, we likely know that it will hold 8 quarts of oil and that it is required by the FAA to fly all day on 4 quarts. Many of us don't even put in 8 quarts, rather, we use 7. Many don't add oil until the dip stick shows 6 quarts or even 5 quarts. The Rotax 912ULS has a range on the dipstick that is acceptable for oil level. So it does not seem critical to have some maximum or close to maximum oil level.

The following assumes this is your aircraft, you are the only one flying it and you know the oil fill history. That means you added the 3 liters at oil change time and noted any other additions.

Now, you go out and check your engine cold. It is at or above the add mark. You know there is zero or some additional oil in the crankcase so if you "burped" it and transferred some or all of that oil to the tank, the oil level in the tank would be equal to or greater than the oil level you measured "pre-burp". In other words, in this example, enough.

We have established that the oil tank contains enough oil and we are reasonably sure since we manage the oil that it does not have too much.

Why burp?
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  #2  
Old 09-02-2017, 01:36 PM
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f1rocket f1rocket is offline
 
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Location: Martinsville, IN
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Good question. I rarely burped mine because it didn't leak a drop nor did it burn any. I checked the level cold because I knew where it would line up.

I'm not sure the Rotax docu would approve but that's what I did.
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  #3  
Old 09-02-2017, 02:10 PM
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Tony_T Tony_T is offline
 
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Location: Lacey, WA
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I don't think you have to burp the engine if you are the sole operator and know where the oil level is.

However, consider that the engine is a dry sump design, in fact there is no sump as such, and if you do a cold start the crankshaft may have to spin in cold viscous oil unless you have moved it out to the oil tank. Also, it can't hurt to turn the prop and pre-pressure, pre-lube the bearings. I know the Merlin engines have a pre-oiler that is run before start-up, but of course the 912 is not a Merlin.

Anyway, I like doing the burp routine, gives me a chance to bond a little with my girl before flying.
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  #4  
Old 09-02-2017, 07:37 PM
jnmeade jnmeade is offline
 
Join Date: Mar 2013
Location: Iowa
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I have been told it's not good to turn over the prop of Continental and Lycoming engines by hand because you just dry scrape the cylindar walls without doing any good - better to get the pump turning fast and get some oil moving.

I'm not inclined to think turning the Rotax over by hand lubes anything. It would be good to hear some definitive info on that question.
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  #5  
Old 09-02-2017, 08:20 PM
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Tony_T Tony_T is offline
 
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Quote:
Originally Posted by jnmeade View Post
I have been told it's not good to turn over the prop of Continental and Lycoming engines by hand because you just dry scrape the cylindar walls without doing any good - better to get the pump turning fast and get some oil moving.

I'm not inclined to think turning the Rotax over by hand lubes anything. It would be good to hear some definitive info on that question.
I don't get even close to a prop on a Lyc. or Cont. The 912 is a different animal entirely. She doesn't have magnetos so hand propping probably won't kill you.

You can see oil pressure on the gauge when you prop it by hand so oil must be moving through the bearings. I don't know about dry scraping the cylinder walls, but Rotax recommends burping the engine to check oil so their engineers are OK with turning it by hand.
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  #6  
Old 09-02-2017, 09:00 PM
jnmeade jnmeade is offline
 
Join Date: Mar 2013
Location: Iowa
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You see oil pressure on the gauge when hand propping the Rotax 912ULS? I'll have to do that and see. If it does build oil pressure I have no objection to that. I'm not sure it's necessary or even useful to "pre-lube" the bearings, though. Thoughts on that?
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