Hi everyone,
Today I started the engine for the first time. It started right up!
However, not being used to a Rotax 914, it is difficult to tell what
engine behaviour is normal. There are two things that make me wonder if
I fall into the normal range:
1) How rough is normal?
Ok, I'm spoiled. Have flown most of my hours in a Cessna with diesel
engine. 4-in-row, 3-blade propeller. These things run as smooth as a car.
With the Rotax, it is quite different. Vibrations are eminent. Have
pneumatically balanced the carbs, checked everything, but can't get idle
reliable and smooth below 1500 rpm. RPM is unstable (varies in a band of
about 100 RPM above 1500 rpm, more below that), runs relatively smooth
between 2200 rpm and 3500 rpm, around 4000 rpm vibrations increase,
didn't go any higher than that. Below 1500 rpm idle is unstable, and
below 1400 rpm the rpm suddenly drops sharply. Had it for a short while
running at 800 rpm, but, let's say, 1000 rpm is pretty much impossible
to get, most of the time it just dies if I try to get below 1400 rpm.
The vibration is not that bad, it is not as if the machine is going to
fall apart, but more like you would expect from a motorbike or so, well,
maybe slightly rougher. I have a two blade prop (Woodcomp SR3000/2W),
maybe it is normal for a two blade to give some vibrations? Haven't
balanced it yet, but it is supposed to be balanced from the factory. Is
this to be expected?
Fuel pressure is 4 psi, RPM drop with both magneto's about 150 rpm
(although difficult to establish because the rpm varies by itself).
All 4 EGT's are equal. Checked the plugs, they seem normal as well.
Front ones appear to receive a slightly richer mixture (see some carbon
deposites, most likely from starting up with choke), the bottom plugs
show slight traces of oil on the outer ring. All show a pretty healthy
tan color on the nose.
Is this RPM instability and roughness normal?
The engine has not been used since delivery around september. Could it
be that I need to clean the carbs? Another possibility (not yet checked)
is that I need to change the idle mixture (maybe somewhat enrichen it)?
Oh, I did check the lifters, they appear to be functional, with no air
trapped inside.
2) How much heat is normal?
I knew in advance that the combination Europa-Rotax is somewhat of a
challenge. Have made some cowling changes with the expectation not to
experience any heat problems. Alas, this thing heats up quickly. About
10 minutes before the coolant (50/50) gets to 130 degrees Celcius.
Cylinder heads (measured with a ring sensor below the cylinder head
bolts) about 10 degrees lower (?).
In fact, I didn't succeed in getting an oil temperature up to the green
zone (about 90 degrees) without getting into the red zone with the
coolant. I doubt whether it will be possible to do some serious power
testing this way.
Is this normal? How long should it be possible to taxi/idle before the
temps go to high? How should one test higher power settings on the ground?
Get about 750 Celcius on the EGT's at 3500 rpm (fronts a little bit
lower than the rears). Is that normal?
Have had the prop on fine with all tests.
Any indications of what is normal are appreciated.
Thanks,
--
Frans Veldman
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