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ronlee
Joined: 25 Dec 2006
Posts: 141
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 Posted: Thu Nov 25, 2010 8:46 am Post subject: Is burping a Rotax 912 necessary |
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There is lots of talk about burping a 912 to get an accurate oil level check. My question is, If the oil level is only down about 1/4 quart before burping is it really necessary to burp? What can it hurt by just starting the engine and letting the normal crankcase pressure evacuate it Now I understand if a great deal of oil has drained into the crankcase it should be burped to prevent, lets say a hydraulic lock or just lots of oil being slung around the crankcase.
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Ron Lee
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Thu Nov 25, 2010 10:09 am Post subject: Re: Is burping a Rotax 912 necessary |
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| ronlee wrote: | | There is lots of talk about burping a 912 to get an accurate oil level check. My question is, If the oil level is only down about 1/4 quart before burping is it really necessary to burp? What can it hurt by just starting the engine and letting the normal crankcase pressure evacuate it Now I understand if a great deal of oil has drained into the crankcase it should be burped to prevent, lets say a hydraulic lock or just lots of oil being slung around the crankcase. |
It's not necessary, no, but it's a good check to make before starting anyway. I.e. it shows the oil return system is actually working and checks for hydraulic lock. Either one of these when trying to start up could be pretty expensive....
LS
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LS
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Thu Nov 25, 2010 10:43 am Post subject: Is burping a Rotax 912 necessary |
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Lucien,
I understand your statement "shows the oil return system is working
properly", but what do you mean by "hydraulic lock", and how would you know
from this procedure if you had one?
Hugh McKay
Rotax 912 UL
Allegro 2000
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Thu Nov 25, 2010 11:28 am Post subject: Re: Is burping a Rotax 912 necessary |
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Hi Hugh,
If you had a hydraulic lock the prop will not turn over on the problem cylinder.
In some cases enough oil or fuel can leak into a cylinder and cause a hydraulic lock which if you try to start the engine could cause a problem since the oil or fuel won't compress. This is usually people that don't do regular prescribed maint. so this issue comes on and the first they know of it is when they try to start their engine. It is more apt to be people that have a high wing and don't shut off fuel. Some times it can be from the way people have installed their engine and related components like the oil tank reservoir. It is people that have damage to rings or a bad float needle valve in the carb, ect.... It really amounts to fuel or oil that has leaked into a cylinder while the plane was sitting and because you had something wrong internally you didn't know about.
Lucien's point is that if you do take the time to rotate the prop then you should find this hydraulic lock by hand and not do damage by just turning the key. If you had a true hydraulic lock and just turned the key it could bend internal parts.
This situation isn't that prevalent and I think you saw it more often years ago, but it still can happen. Here is a good place to say, "Do the 100 hr. inspections that are in the "Line Maint" manual and save money on expensive fixes or en flight problems.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Thu Nov 25, 2010 11:53 am Post subject: Is burping a Rotax 912 necessary |
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Thanks Roger. In the past I have turned the prop to get the "gurgle", but
after questioning why, the only answer I got was to check the oil level in
the oil tank. I now understand what you mean by "hydraulic lock". Even
though I have a high wing plane with wing tanks (Allegro 2000), no fuel can
drain from the wing tanks, or the main tank by gravity. Here's why. The wing
tanks drain by gravity only to the main fuel tank that is located under the
seat area of the plane. From there the fuel is pumped up to the engine. The
oil tank is set such that oil cannot drain to the cylinders. However, just
in case, I will return to "burping" the engine to check for Hydraulic lock.
Too many $ tied up in the engine not to do so.
Hugh
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Thu Nov 25, 2010 12:30 pm Post subject: Re: Is burping a Rotax 912 necessary |
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Hi Hugh,
The lock up is fairly rare so I wouldn't loose any sleep. If were more prevalent we would be reading a lot more about it.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Thu Nov 25, 2010 7:14 pm Post subject: Is burping a Rotax 912 necessary |
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If oil somehow is able to leak into a cylinder irt will act like a block and
prevent the crank form turning. If you try to start the engine and it fires
on another cylinder it is possible to blow the head off the locked cylinder.
Big engines especially radials where there are cylinders at six O'clock are
especially prone to hydraulic lock. For that reason the operating
instructions usually include watching for so many blades to turn past the
cockpit before turning on the ignitions. If you ever saw a radial start up
the first thing noticeable is the fact they always start with a great
production of smoke from burning oil.
Hydraulic lock may not be as much of an issue with the boxer style 9xx
engines but I guess it is possible for oil to leak into the cylinders
especially if the plane is not parked level or if the oil reservoir is
mounted higher than the cylinders. Burping seems to be a simple quick way
to kill two birds with one stone... first you know you have enough oil and
second, you know that you won't be instantly destroying your engine when you
start it.
Reminds me of what my instructor on piston engines told me... the worst
thing you do to a piston engine in normal service is start it!
Noel
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Noel Loveys
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Sun Nov 28, 2010 3:48 am Post subject: Re: Is burping a Rotax 912 necessary |
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When Roger says cylinder hydraulic locks, I think back to the big
radials of yesteryear. Those are the guys who had frequent oil
locks in the bottom cylinders.
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