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When to BURP and why

seagull

Well Known Member
I am starting this thread since there seems to be a lot of opinions and willing discussion on the topic.

I read this from Rainbow Aviation; They seem to say the purpose of burping is to read the engine oil level and the Rotax 912 is not the typical dry sump system.

It will be interesting to hear opinions backed with knowledge not "my neighbor pilot told me....."

https://electricmotorglider.com/wp-content/uploads/2017/10/Burping-The-Rotax-912-web.pdf
 
I am starting this thread since there seems to be a lot of opinions and willing discussion on the topic.

I read this from Rainbow Aviation; They seem to say the purpose of burping is to read the engine oil level and the Rotax 912 is not the typical dry sump system.

It will be interesting to hear opinions backed with knowledge not "my neighbor pilot told me....."

https://electricmotorglider.com/wp-content/uploads/2017/10/Burping-The-Rotax-912-web.pdf

Nots sure what there is to say, that's the procedure for checking the oil, it's easy and it works.
 
Nots sure what there is to say, that's the procedure for checking the oil, it's easy and it works.

There are some folks that suggest the burping is to prevent hydro lock so It is important to be done at the beginning of the flight.

I burp at the end of a flight, check oil level, done. No burping done before the next flight, never caused a problem or heard of anyone having a problem.

Maybe in real cold climates it is helpful to move the parts to get some oil on them before the starter takes over.
 
There are some folks that suggest the burping is to prevent hydro lock so It is important to be done at the beginning of the flight.

Are these people flying Rotax or Radials? You “burp” the Rotax to put the oil back into the can, wether that’s to check the oil level or to prepare for an oil change. It moves the oil into the can via leak down compression past the rings. That’s why you go slow to allow the compression to act on the oil. As for checking the oil at the end of the flight, why deal with the hot oil cap and dipstick? I check it before the flight while the cap and oil is cool, plus you know what you have right before you fly. I suppose if you check it after the last flight, and you know no one has flown it, and it lives in a hangar where a leak would be obvious, then you can assume the oil is good for your next flight, but why not just check BEFORE you flight instead of after, and skip the assumptions (and the hot cap/dipstick)?
 
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Are these people flying Rotax or Radials? You “burp” the Rotax to put the oil back into the can, wether that’s to check the oil level or to prepare for an oil change. It moves the oil into the can via leak down compression past the rings. That’s why you go slow to allow the compression to act on the oil. As for checking the oil at the end of the flight, why deal with the hot oil cap and dipstick? I check it before the flight while the cap and oil is cool, plus you know what you have right before you fly. I suppose if you check it after the last flight, and you know no one has flown it, and it lives in a hangar where a leak would be obvious, then you can assume the oil is good for your next flight, but why not just check BEFORE you flight instead of after, and skip the assumptions (and the hot cap/dipstick)?

After flying the oil is thinner and transfers back to the canister much easier, 2-3 prop revolutions, vs when it is cold about 10 turns. I get a more accurate reading on the dipstick when it is warm.
Yes I am fortunate the plane lives in its own hangar and I am the only pilot.

To each his own, in the end it really doesn't matter when you burp it and burping isn't related to better starting.
 
Not sure why one would check the oil level after a flight. I’m more interested in having oil in an engine I’m about to stake my life on for an imminent flight.

For those who don’t want to burp, fine. Let me know how that works out for you the 0.0001% of the time it catches up with you.😝
 
Not sure why one would check the oil level after a flight. I’m more interested in having oil in an engine I’m about to stake my life on for an imminent flight.

For those who don’t want to burp, fine. Let me know how that works out for you the 0.0001% of the time it catches up with you.��

If you feel things are happening to your aircraft when you are away from it, either people messing with it or fluids leaking out you should be doing more than a pre-flight before you fly.

If your oil level changes with a cold engine sitting in a hangar then I can only imagine what is leaking out when it is hot and under pressure, let me know how that is working out. :eek:

BTW, in posting this topic I was looking for OTHER reasons, (besides checking oil level), to burp the engine. Some have said it was to prevent hydro locking which I haven't read from Rotax. Whether you check oil before or after a flight, or never at all isn't what this discussion was meant for.
 
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BTW, in posting this topic I was looking for OTHER reasons, (besides checking oil level), to burp the engine. Some have said it was to prevent hydro locking which I haven't read from Rotax. Whether you check oil before or after a flight, or never at all isn't what this discussion was meant for.

Actually, the burp procedure does not "prevent" hydraulic lock - it is just a check for hydraulic lock. If you hand-turn four blades then you know that all four combustion chambers are free of oil and it is OK to run the electric starter motor. Some 912 installations (not RV-12) have oil tank mounted high with respect to engine, and I'm told, oil can sometimes syphon back into the engine and fill the crankcase. If this happens then oil will weep past the piston rings and pool in the combustion chambers. If you run starter motor the oil will not compress (hydraulic lock) and you bend connecting rods and other bad things will happen.

Yes, the 912 is a dry-sump engine where oil is scavenged from the crankcase to a separate oil holding tank. Rotax accomplishes this rather ingeniously, not with a scavenge pump, but with air pressure inside a non-vented crankcase. Blow-by from the cylinders causes a positive pressure in the crankcase and this forces the oil back to the holding tank. Dry-sump design is used in aircraft to keep oil from splashing up against crankshaft – this would cause foaming of the oil and would also rob valuable horsepower.

Also to note... with a sealed crankcase there is no moisture ingression and corrosion (rust) is much better controlled. Oil temperatures need to be high enough the boil off water vapor from the combustion process.

You really don’t have to burp the engine dry in order to have a safe starting sequence. Any residual oil in the crankcase will transfer back to the holding tank when the engine starts.

Having said all this... I subscribe to a full burping procedure but I’m confident that you can hand-turn four blades to verify no hydraulic lock and then start the engine with no damage.
 
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Lockwood Aviation has a several videos on the Rotax 912. The Gentleman in the video says that burping is only for checking oil level. He further states that if you check the level before burping and it is in the correct range, just start the engine and go fly.
 
I would at least hand-turn four blades before engaging electric starter. Shortcuts can result in expensive repairs...
 
Rotax specifies the burping procedure for only one purpose.......
To accurately check the oil level.

If you look at the shape of the engine case, you will see that even if the majority of the oil drained from the tank into the engine (it can't all drain because the pick-up tube doesn't go all the way to the bottom of the tank), it would not be enough to fill the case volume that is below the cyl, so the chance of oil filling a cyl bore enough to cause a hydraulic lock is extremely remote (not going to say zero chance because I have seen instances of people severely over filling with oil).

There is also no danger of "wiping cyl bores clean" of protective oil by moving the prop. If the engine isn't burning any oil in normal operation, there isn't any oil on the cyl walls to be wiped off, after it is shut down.

One major benefit of of doing the oil level check when the engine is warm is it give you the most accurate level reading because of the much lower oil viscosity making it flow much easier.

A common oil level check mistake is doing in the cold of winter after the airplane has been sitting for a while and some oil drain-back to the engine has occurred. Because the oil is very thick, once you have gotten it to burp, there will still be a thick coating of oil on the inside of the engine case that hasn't returned to the tank. If you add oil based on the appearance of it being slightly low, it is common to have it over filled after just a couple of instances. This is one scenario where checking the oil after a flight is a good procedure to use. You don't have to do it when it is scalding hot..... open the oil door to vent the engine compartment while you put the airplane away. Once you have having everything else taken care of and the door closed, it is usually cooled enough that you can do an oil level check as a last thing.
Then when arriving for the next flight, as long as there is no puddle of oil on the floor, you know precisely what the oil level is.
As already mentioned, this may not work as well with shared usage airplanes.
 
Last week I was working with a gentlemen who is about to finish his RV-12. He hopes to be flying it in August. In preparation for our flying, I reread the POH and the Flight Training Supplement. One of the things that I learned (I probably knew it before but forgot it) was there is an alternate procedure for burping. It is to take the oil cap off and then run the starter for 10 seconds with the ignitions off and then check the oil.

Does anyone do this instead of burping?

Thanks.

John
 
IMHO, using the starter to burp the engine does not produce the desired result. The starter turns the engine over too fast to produce the required cylinder blow-by required to force the crankcase oil up into the oil tank. In addition, extra unnecessary use of the starter only results in added wear on the starter and the sprag clutch assembly ($$$).
 
In addition to burping for oil level check, and verifying no hydraulic lock, it’s a good idea to hand-turn a few prop blades to ascertain general engine health.

• Compressions same on all four cylinders?
• Backlash in gearbox sound/feel as it did on previous flights?
• Drive dogs on slipper clutch make same clicking noise when pistons go over TDC?

Always better to determine a problem on the ground than to discover problem in the air...
 
Last week I was working with a gentlemen who is about to finish his RV-12. He hopes to be flying it in August. In preparation for our flying, I reread the POH and the Flight Training Supplement. One of the things that I learned (I probably knew it before but forgot it) was there is an alternate procedure for burping. It is to take the oil cap off and then run the starter for 10 seconds with the ignitions off and then check the oil.

Does anyone do this instead of burping?

Thanks.

John

I tried this a couple of times, and it didn’t work for me.
 
How many blades are on your prop and how does the 2.43:1 gear reduction relate to the number of blades pulled and the number of combustion chambers purged or checked?
 
Last week I was working with a gentlemen who is about to finish his RV-12. He hopes to be flying it in August. In preparation for our flying, I reread the POH and the Flight Training Supplement. One of the things that I learned (I probably knew it before but forgot it) was there is an alternate procedure for burping. It is to take the oil cap off and then run the starter for 10 seconds with the ignitions off and then check the oil.

Does anyone do this instead of burping?

Thanks.

John

How many blades are on your prop and how does the 2.43:1 gear reduction relate to the number of blades pulled and the number of combustion chambers purged or checked?

This method was developed (with Rotax's blessing), primarily for the flight school environment.
They have multiple pilots flying the airplane during any given day, and the oil is likely to be checked by every pilot (it is a training environment after all, so students are being taught to always check, and feedback indicated that they would prefer to not have students turning the prop by hand more than necessary.
With somewhat warm oil the starter rotation method works well.
With the engine totally cold, it probably wont give a 100 % accurate level reading but it will generally move enough oil to confirm that the level is at least in the safe / normal operating zone which is the primary purpose for doing the level check.
 
Not sure why one would check the oil level after a flight. I’m more interested in having oil in an engine I’m about to stake my life on for an imminent flight.

For those who don’t want to burp, fine. Let me know how that works out for you the 0.0001% of the time it catches up with you.😝

In 350 hours over 5 years I don't recall using more than 1-2 quarts of oil and even then I wasn't actually convinced it "used" any. Is anyone having to add oil to the 912 ULS?
 
In 350 hours over 5 years I don't recall using more than 1-2 quarts of oil and even then I wasn't actually convinced it "used" any. Is anyone having to add oil to the 912 ULS?
Our newest partner has added half a cup or so twice. The engine promptly blew it overboard, maintaining the oil level right about the middle of the flat on the dipstick where it started.

So no, it's not using oil in any appreciable quantity. About 600 hours TT here, plane built in 2011 and I bought it in 2015.
 
When I burp an engine I do it only for the purpose of checking oil.

I get it. Rotax says burp the engine to check accurate oil level...

There is no danger in turning a 912 Rotax by hand. Ignition switches can even be left on. No spark will occur because Capacitive Discharge Ignition gets its voltage from separate generator coils. Engine needs to spin several hundred RPM to power the CDI's.

Why not use this opportunity to develop a mental picture of how a healthy engine feels / sounds when turned by hand?

• Compressions same on all four cylinders?
• Backlash in gearbox sound/feel as it did on previous flights?
• Drive dogs on slipper clutch make same clicking noise when pistons go over TDC?

Wouldn't it be better to discover weak compression on one cylinder prior to flight? I don't let other people burp my engine. I know exactly how it should feel and sound when turned by hand. Day one of flight training - always better to determine a problem on the ground than to discover problem in the air.
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I get it. Rotax says burp the engine to check accurate oil level...

There is no danger in turning a 912 Rotax by hand. Ignition switches can even be left on. No spark will occur because Capacitive Discharge Ignition gets its voltage from separate generator coils. Engine needs to spin several hundred RPM to power the CDI's.

Why not use this opportunity to develop a mental picture of how a healthy engine feels / sounds when turned by hand?

• Compressions same on all four cylinders?
• Backlash in gearbox sound/feel as it did on previous flights?
• Drive dogs on slipper clutch make same clicking noise when pistons go over TDC?

Wouldn't it be better to discover weak compression on one cylinder prior to flight? I don't let other people burp my engine. I know exactly how it should feel and sound when turned by hand. Day one of flight training - always better to determine a problem on the ground than to discover problem in the air.
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All good points Jim, and that is just one benefit of personal aircraft ownership... becoming intimately familiar with an airplane.

But all of the things you mentioned are not a good argument for turning the prop and checking the oil level, just before starting for a flight.
These same things can be checked for and observed after a flight as well.

The chance of any of them changing from when the airplane was last put away, is nearly zero as long as the airplane hasn't sat for an extended period of time. If that is the case, then I fully agree that exercising the engine by hand is probably a good idea.

One argument for this is in regards to cyl compression.
In the years I have been working with the Rotax 912, I have seen at least a couple of instances (usually in the dead of winter when it is very cold) where a couple of cyl. had indications of low compression when burping for an oil level check.
After starting the engine, running for about 1 minute, and then shutting it down and doing the check again, all of the cyl had good compression.
 
Regarding oil usage - -

I just finished changing oil and the rest today. Since Rotax changed the required time to change oil to 100 hours if only premium auto fuel, I add a little less than a quart throughout the 100 hours. I burp when warm, and never fill above 1/2 way on flat area of stick. Hours as of today 1,425. I changed at 25 hours as recommended, and every 100 since. Engine has never really changed since new. I will say, the first 50 hours it uses less oil. The second 50 hours is when it starts to use a very little. A quart in 100 hours I consider near nothing. By the way. I always remove the cooler and drain the hoses.
 
Why not use this opportunity to develop a mental picture of how a healthy engine feels / sounds when turned by hand?

• Compressions same on all four cylinders?
• Backlash in gearbox sound/feel as it did on previous flights?
• Drive dogs on slipper clutch make same clicking noise when pistons go over TDC?

Wouldn't it be better to discover weak compression on one cylinder prior to flight? I don't let other people burp my engine. I know exactly how it should feel and sound when turned by hand. Day one of flight training - always better to determine a problem on the ground than to discover problem in the air.
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If you are the only person flying the airplane WHY wouldn't you notice the above items the last time you flew it, different sounds, vibration, etc? All of those things would be more obvious on a running / idling engine. The condition of those things will not change sitting in the hangar for a few days.
 
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If you are the only person flying the airplane WHY wouldn't you notice the above items the last time you flew it, different sounds, vibration, etc? All of those things would be more obvious on a running / idling engine. The condition of those things will not change sitting in the hangar for a few days.

Impossible to notice weak compression on one cylinder of a running engine regardless of speed. Likewise gear backlash is very subtle especially with a hunting (uneven) gear ratio. My contention is that a lot can be gleaned by hand-turning the engine.
 
Impossible to notice weak compression on one cylinder of a running engine regardless of speed. Likewise gear backlash is very subtle especially with a hunting (uneven) gear ratio. My contention is that a lot can be gleaned by hand-turning the engine.

If you have the feel to notice that one cylinder is down on compression you should also be able to tell that the performance is down from the previous flight.

Compression loss does not suddenly fail unless you break a ring, it is a slow process something that shows up when you do your 100 hr. If you loose a ring you will most likely start using oil, that's where the oil check comes in handy.

The same with gear backlash, it does not suddenly get bad so You would have to remember how the lash felt 6 months ago to compare it to today.

You could take your logic to the extreme and check tire pressure, cable tension, etc before every flight, but we don't.

If you really want to be safe do a conditional inspection before each flight.

Sorry for the rant, I haven't had my coffee yet.
 
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If you have the feel to notice that one cylinder is down on compression you should also be able to tell that the performance is down from the previous flight.

Compression loss does not suddenly fail unless you break a ring, it is a slow process something that shows up when you do your 100 hr. If you loose a ring you will most likely start using oil, that's where the oil check comes in handy.

The same with gear backlash, it does not suddenly get bad so You would have to remember how the lash felt 6 months ago to compare it to today.

You could take your logic to the extreme and check tire pressure, cable tension, etc before every flight, but we don't.

If you really want to be safe do a conditional inspection before each flight.

Sorry for the rant, I haven't had my coffee yet.

I'm going to suggest only one more thought... did you ever have a stuck exhaust valve? Engine ran fine on previous flight. During preflight - zero compression on one cylinder. Huge leak heard through exhaust system when engine turned by hand. You do what you want. I will play safe...
 
I'm going to suggest only one more thought... did you ever have a stuck exhaust valve? Engine ran fine on previous flight. During preflight - zero compression on one cylinder. Huge leak heard through exhaust system when engine turned by hand. You do what you want. I will play safe...

A stuck valve is VERY rare on a Rotax that is run on mogas, (as recommended),
AND if the valve was stuck you would notice it on start up and presumably not fly.

Just to set things straight, I am not posting for you benefit.
 
I had a stuck valve on a Cessna 150 (Continental O-200A). It wasn’t obvious until the less than enthusiastic takeoff run which I aborted.
 
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