Jonathan,
It is not uncommon for the oil level in the tank to drain down overnight.
Even on a new engine. The tank can drain into the crankcase two ways on a
912UL (S). If the tank is full, and the return line has oil in it, it siph
ons down into the crankcase until the siphon is broken. That is only a sma
ll amount of oil on the dipstick.
The other is through the feed line, through the oil cooler and into the oil
pump. The oil pump has tight clearances, but thin oil will drain quite ra
pidly through the pump into the crankcase via the many feed passages. You
are right, it could be a seal in the oil pump was not changed on your rebui
ld or the oil pump shaft has worn beyond limits (check service bulletin 912
-032). This internal seal leak doesn=92t show normally, until the oil pump
case to pump seal begins to leak. The case to oil pump is just sealed wit
h 515. This is an easy fix and all external and right up front for your me
chanic. So Look.
On the other hand, you would have low oil pressure if your pressure relief
spring/ball were stuck so I doubt that is a problem.
Lastly, if you have a feed oil line leak at the tank, or internal in the pu
mp, air is introduced into your feed line to the oil pump. This prevents o
il getting to the pump, but doesn=92t really affect the burp. If your oil
pressure comes up quickly and when you pull the plugs and spin the engine b
y hand, you get oil pressure, that is not a factor. That is a difficult is
sue to trace. The only way to check is try using light air pressure on the
oil tank overflow / vent line and remove listen for the oil moving or remo
ve the oil feed at the pump and check for air. I really doubt that is a pro
blem.
Note:
I found Mobile one synthetic drained quickly and the Aeroshell Sport plus 4
less. I would not be concerned. BUT:
50 blades on a 912S is quite a lot of spinning. (Normal for my old 914.)
If you pause on each compression, it should only be about 10 blades of spin
ning to get a gurgle, but that is only based on new (er) 912S engines. The
912 and 914 tend to take more spinning to the verge of a heart attack on m
ine.
Do check for static leaks on your fittings as a Rotax will not leak oil ext
ernally unless something is wrong. If you have oil anywhere on the outside
of your engine, oil pump, gearbox, or oil cooler, please investigate and s
olve it. If all is high and dry, it is probably just that shaft oil seal o
n the oil pump is leaking internally. This is not a huge problem, but warr
ants checking.
Best Regards,
Bud Yerly
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Window
s 10
________________________________
From: owner-europa-list-server@matronics.com <owner-europa-list-server@matr
onics.com> on behalf of jonathanmilbank <jdmilbank@yahoo.co.uk>
Sent: Wednesday, May 30, 2018 5:53:47 PM
Subject: Europa-List: Gurgling (burping)
>
My 912ULS engine has done 250 hours since complete strip-down and rebuild a
fter I bought it from an acknowledged Rotax engine expert. The three others
who share the Europa with me are all happy with how sweetly it runs. The c
ompressions were measured very recently and are excellent (close to 200 psi
). The oil pressure is good being in the vicinity of 4 bar. BUT....
Nine times out of ten the oil drains quickly (overnight) from the tank to a
level below the flat on the dipstick. This wasn't always so and has become
worse over time. It used to take about a dozen compressions done quite slo
wly to push the oil back into the tank, while these days it can often take
50 or more compressions. Why?
My supposition is that the oil escapes past the oil pump and the rate of es
cape depends on the position of the pump lobes when at rest. So if the oil
pressure remains good in flight, what's changed? Perhaps the oil pressure r
elief valve is sticking in some way?
Your experience and knowledge of likely causes would be gratefully received
.
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