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  #1  
Old 09-02-2017, 02:23 PM
jnmeade jnmeade is offline
 
Join Date: Mar 2013
Location: Iowa
Posts: 128
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, 02:36 PM
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f1rocket f1rocket is offline
 
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Location: Martinsville, IN
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Default

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, 03:10 PM
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Tony_T Tony_T is offline
 
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Location: Seattle, 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, 08:37 PM
jnmeade jnmeade is offline
 
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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, 09:20 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, 10:00 PM
jnmeade jnmeade is offline
 
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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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  #7  
Old 09-12-2017, 08:09 PM
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Tommycat Tommycat is offline
 
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Location: North-western Illinois
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Default Great video...

Here's a link to a video on the Rotax provided by another member, that I found to be very informative...Burping included.


TommyCat courtesy link...


Regards,
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Last edited by Tommycat : 09-12-2017 at 08:10 PM. Reason: Spelling :-)
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  #8  
Old 09-13-2017, 12:22 PM
Jolly Jolly is offline
 
Join Date: Nov 2016
Location: San Francisco, CA
Posts: 25
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It's funny how new people to Rotax have never studied Rotax history and know nothing about its history or engine and part specs. Knowing about 10 engines isn't like getting info from world use.
Do Rotax engines get hydrolock. Yes. Back when the Kitfox aircraft always mounted their oil tanks too high and when using the old Rotax oil filter they had hydrolock issues. Even though Rotax has changed their filters over the years to help prevent that it still happens to some engines. A friend of mine went to do a pre-buy last week on a Sport Cruiser. Before they started it they went to rotate the prop and it came to a stop. They removed all the bottom plugs and oil poured out of the #2 cyl. If they had turned the key that would have bent a lot of expensive parts. That bill would have been around $8K+. The had another about a month ago in Texas. Hydrolock issues have been greatly reduced over the years, but they can and still do happen occasionally. Some gambles might be worth it to some folks, but some aren't. If you want to play gamble better just head to Las Vegas.

The oil level check is not as accurate as some have been led to believe. It certainly puts you in the ballpark, but it can lie to you and usually on the low side. You are right that rotating the prop should make it only go higher on the stick because the oil that has settled in the bottom of the case gets pushed on back to the tank with air pressure.
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  #9  
Old 09-13-2017, 02:01 PM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
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Default Another note from experience - -

I have found that if you spend a little extra time taxiing to shut-down, it seems to leave a little more oil in the engine. My theory is that while warm, there is less blow-by, and if you use very light throttle getting to shut-down, maybe not as much oil gets pushed back to the tank. I like to check the oil level by burping right after shut-down. Takes less amount of turns, and you don't have to check it next time if no oil is on the floor. The RV-12 design I don't believe will cause hydro-lock. Anyway, my story - - -. Over-filling because you did not burp it will waste oil, because it over flows any extra you put in. I try to keep level about mid way on flat of stick.
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  #10  
Old 09-13-2017, 08:46 PM
R100RS R100RS is offline
 
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Location: USA
Posts: 31
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Jolly, you wrote the following less than a year ago: "Just saw this on the Rotax Owner forum. A new service class for Rotax annuals and inspections that is supposed to be all hands on. Might be cool to go to. I'm a newbie so I think I'll go. I can use the help on my 12 and I need to know more about my engine."

Funny, you don't seem to be such a newbie, based on your comment earlier today (see #8, above). So, how is the "12" build coming? What's up with the mystery?

Last edited by R100RS : 09-13-2017 at 08:57 PM.
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