I burp exactly as described after the last flight of day.
There is no siphon back even over several days between flight.
I think there is an air gap in the return to the tank, otherwise you wouldnt
hear
the burp, that prevents siphoning.
Alan
Sent from my iPad
> On 21 Aug 2024, at 03:05, h&jeuropa <butcher43@att.net> wrote:
>
>
> I have a different view on the oil check burping.
>
> According to the Rotax Operators Manual,
>
> 1. Remove bayonet cap from the oil tank, turn the propeller
> slowly by hand in direction of engine rotation several
> times to pump residual oil from the engine into the oil
> tank.
>
> 2 It is essential to build up compression in the combustion
> chamber. Maintain the pressure for a few seconds to let
> the gas flow via the piston rings into the crankcase. The
> speed of rotation is not important but rather the continuous
> pressure and the amount of gas which is transferred
> into the crankcase.
>
> 3 This process is finished when air is returning back to the
> oil tank and can be noticed by an audible gurgle from
> the open oil tank.
>
> 4 Check oil level and add oil if necessary.
>
> My understanding is that over time oil siphons from the tank back to the
> crankcase
after the engine is shut down. "Burping" the engine uses compression to
force the oil in the crankcase back into the tank.
>
> We operated our 914 for nearly 1300 hours until the compression in several
> cylinders
got low enough that the engine no longer performed well. They were around
60/80 psi with a differential test and 85 psi with a conventional test.
>
> For the last several years we were unable to get the engine to burp prior to
start, even rotating it 50 or 60 revolutions! We quit trying and instead when
shutting down the engine, we checked the oil immediately since the tank was full
and the siphoning had not yet started.
>
> Our new 914 burps after just a few turns and the compression is much higher,
it's difficult to rotate.
>
> Notice that Rotax says to rotate slowly and to maintain the pressure to let
> the
gas flow. That's exactly how we do it. You can feel the pressure drop and
hear the air flowing.
>
> I'm surprised that burping after the last flight of the day and then checking
the oil level the next day gives a satisfactory result. I'd think the oil would
siphon back to the sump during that time.
>
> Just my thoughts and experience.
>
> Jim Butcher
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=513795#513795
>
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