On 10/04/2011 11:24 PM, zwakie wrote:
>> Can anyone confirm that the oil pump indeed prevents air from creeping back
into the hose and prevent oil from flowing into the engine
The oil pump is just a rotary type of pump, when not operating it allows
oil and air to leak into either direction.
- is it by any chance the hydraulic valve tappet that takes care of
this?.
There is an SB about this: if you have got any air in the system you
have to check that no air remains trapped in the valve tappets. I have
been forced to go a few times through this procedure but I'd rather
avoid it. If some air remains in a valve tappet it will quickly destroy
the associated valve train.
Please check the Rotax installation manual (not the one from Europa but
---From Rotax) for more information, also about the best locations for
lubrication components.
>> Assuming that the oil pump does indeed stop oil and air from flowing in
>> either
direction, I would think that the 'pipe' that sucks oil from the oil tank
prevents
siphoning from that end because it sits well below the oil tank's oil
level (preventing air from entering that section). Is this reasoning correct?
No. Oil inside the engine continues to "drip" into the sump, and
therefor a small suction force remains in the oil feed lines. It is
possible (as many have found out) that the entire contents of the oil
tank slowly siphons into the engine. (This is the reason you have to
rotate the prop by hand before starting the engine, so if the oil leaked
into a cylinder and causes a hydraulic lock you will find out about it
before engaging the starter and causing a few thousand bucks of damage
with just one push of a button).
If there is a small leak in the oil suction hoses or fittings at a
higher spot (above the oil tank level), air will be slowly sucked in.
That is why it is recommended to keep radiators and such things well
below the oil level of the oil tank. In that case if there is a leak,
air won't enter but instead oil would slowly leak out. Less harmful, and
much more visible. Also, some leaks are too small for oil, but large
enough for air. So I have routed all hoses and oil components below the
oil tank level just to be safe. And I'm glad I did: even with the high
quality oil fittings I've seen the sockets becoming "wet" over time,
indicating that it is not a 100% air tight fit. If such a fitting would
have been located above the oil tank level for sure an air bubble would
have formed there over some time.
And no, it is not a good idea to raise the oil tank to create more
"clearance": Rotax has some definite rules about the height of the oil
tank relative to the engine and you'd better stay well into the allowed
range.
It is all about chances: How big is the chance that you have a small
leak in a hose or fitting? How big is the chance that subsequently a
valve tappet fails to release the air? It might be a small chance
overall but why not choose for the safest way of building the system?
Anyway, I'm not familiar with the Europa classic oil configuration, it
might be that your idea about the location of the heat exchanger would
work. Then again, the coolant connection of the engine is on the rear of
the engine, so you still have the option to put the heat exchanger over
there.
About the hoses: My experience is that while rubber hoses might still be
ok for a few years more, it is often not a good idea to reroute them or
mess with them in any way once they have been in operation for some
time. The rubber has hardened (or softened), became more brittle, etc.
When I changed my cooling system I also intended to reuse the old stuff
but after finding out the condition of these hoses (with only one year
flying time) I quickly abandoned that idea, ripped it all out and
installed first class coolant and oil hoses. I was particularly
concerned about a specific Europa supplied oil hose, the 90 degree elbow
at the engine oil inlet. That elbow had become very mushy, swollen, soft
and sticky. Maybe it was an exemplary fault, but still a good reason why
to distrust rubber hoses. Rubber and oil are not a perfect combination.
If you use Mogas, traces of ethanol will find its way into the oil
system, attacking the rubber hoses from the inside. Some rubber hoses
have been known to delaminate internally, causing invisible blockages.
So, once you are at it and purging the oil system anyway, better get rid
of the rubber hoses at the same time.
Frans
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