Rotax 912 questions

Hi all.

I have recently completed my airplane and have begun taxi testing. For
an engine I chose the Rotax 912. I purchased the engine from a
Trade-A-Plane ad where it was advertised as being "new in the box".
When I inspected the engine prior to buying it did appear to be brand
new and was still bolted into the shipping container. I bought the
engine in 1999 and it has not been run until recently. Not only that,
but the serial numbers indicate that the engine was 5 years old in
1999. The age of the engine probably does not matter, however, I
mention it only as background information.

I have been happy for the most part with the engine. But there are some
odd things about it. I have no experience with 912's so I thought I'd
seek some wisdom from others. First, the engine has an incredible
amount of gearbox chatter at around 1600 all the way to about 1950 RPM.
It's swinging a large 72" wood prop. I have set the idle to 2000 RPM in
an effort to get out of the gearbox chatter zone, but with a 72" prop
that still results in quite a bit of thrust. In other words, when I
chop the power on landing (when I get to that point) I'll still have a
bit of power pulling me along. Is that normal? Also, I know the 2
stroke Rotax's are notorious for gearbox chatter, but you don't hear as
much about that from the 912. Is my engine behaving normally? What are
others doing to deal with the chatter?

The other unusual thing about the engine is that it is very cold
natured. It takes a very long time for the water temp to come up. I've
even gotten to the point of covering up half the radiator with a piece
of cardboard until the temperature comes up. I'm starting to suspect
that perhaps I have a thermostat that is stuck open (perhaps due to the
prolonged time in storage). Is that reasonable or is that normal
behavior for the 912 ?

Thank you in advance for any help or advice you can offer.

- R. Parsons

"RPar" wrote in message

The other unusual thing about the engine is that it is very cold
natured. It takes a very long time for the water temp to come up. I've
even gotten to the point of covering up half the radiator with a piece
of cardboard until the temperature comes up. I'm starting to suspect
that perhaps I have a thermostat that is stuck open (perhaps due to the
prolonged time in storage). Is that reasonable or is that normal
behavior for the 912 ?

If the temperature comes up to hot quicker with the radiator part covered,
you have a stuck thermostat. For the temperature to get stabilized, where
you don't see it rising and dropping a couple of degrees as the thermostat
opens and closes, is another story. (hot soak)

The radiator should not even feel warm, until the engine temperature is
almost up to normal. Is it doing that?

The thermostat is the cheapest thing in a cooling system, also the quickest
to go bad. I would not even consider running an engine that old without
replacing it.
--
Jim in NC

You are asking a news group instead of an authority such as Lockwood, a
certified Rotax repair station? http://www.lockwood-aviation.com/

OK here goes:

A five (or ten!) year old 912 certainly should have been gone through
before installing it on your airframe. It will need new rubber seals on
the water pump as a minimum. The gear box on the 912 80 HP (black valve
covers) has been very good. Not true with the 912S 100 HP engine (with
the green valve cover). Rotax has added a slipper clutch and a higher
torque starter for the 912S. Your problem may be related to the prop.
Does it meet the inertia spec for the Rotax? Too high an inertia will
eat your gear box.

Have you read the installation manual at www.rotax-owner.com and
signed up for service bulletins?

You are asking a news group instead of an authority such as Lockwood, a

certified Rotax repair station? http://www.lockwood-aviation.c=ADom/


OK here goes:


A five (or ten!) year old 912 certainly should have been gone through
before installing it on your airframe. It will need new rubber seals on

the water pump as a minimum. The gear box on the 912 80 HP (black valve

covers) has been very good. Not true with the 912S 100 HP engine (with
the green valve cover). Rotax has added a slipper clutch and a higher
torque starter for the 912S. Your problem may be related to the prop.
Does it meet the inertia spec for the Rotax? Too high an inertia will
eat your gear box.


Have you read the installation manual at www.rotax-owner.com and
signed up for service bulletins?

I've talked to Lockwood about the chatter. They did not seem to think
it was out of the ordinary. I would feel better if I had some input
from people running them though.

I'll have to check the inertia spec. It was professionally made for the
912 so I assume that it is correct, but it definitely never hurts to
check.

I did read the installation manual and yes I do get the bulletins. My
912 had to have the oil pump drive pin and new stator assembly
installed ($$$). This was performed, along with a complete inspection,
prior to installation and first start-up.

Thanks for your input.

- RP


You are asking a news group instead of an authority such as Lockwood,
a
certified Rotax repair station? http://www.lockwood-aviation.c=AD=ADom/

OK here goes:


A five (or ten!) year old 912 certainly should have been gone through
before installing it on your airframe. It will need new rubber seals
on


the water pump as a minimum. The gear box on the 912 80 HP (black
valve


covers) has been very good. Not true with the 912S 100 HP engine (with

the green valve cover). Rotax has added a slipper clutch and a higher
torque starter for the 912S. Your problem may be related to the prop.
Does it meet the inertia spec for the Rotax? Too high an inertia will
eat your gear box.

Have you read the installation manual at www.rotax-owner.com and
signed up for service bulletins?

G'day

Where is the thermostat located in the Rotax cooling system?


Regards

Ian




If the temperature comes up to hot quicker with the radiator part covered,
you have a stuck thermostat. For the temperature to get stabilized, where
you don't see it rising and dropping a couple of degrees as the thermostat
opens and closes, is another story. (hot soak)

The radiator should not even feel warm, until the engine temperature is
almost up to normal. Is it doing that?

The thermostat is the cheapest thing in a cooling system, also the
quickest
to go bad. I would not even consider running an engine that old without
replacing it.
--
Jim in NC

It's not. Upon reviewing the engine diagrams it appears that the 912
has no thermostat at all.

- Rob

RPar a écrit :
It's not. Upon reviewing the engine diagrams it appears that the 912
has no thermostat at all.

- Rob


Hi Rob and all,

Yes there is no thermostat inside the 912. I'm a bit surprised as you
should have studied the installation diagrams when installing your engine.
Without knowing which type of aircraft, radiators, and details of layout
it is difficult to give an advice.

Regards,

Gilles Thesee
Rotax 914 MCR 4S

"GTH" wrote

Yes there is no thermostat inside the 912.

Oh, that's just grand. More excellent Rotax engineering. I had almost
convinced myself that the 912 and 914 migt be a decent enough engine, (to
trust you life on) compared to the other Rotax products. I'm rapidly
changing my mind.

I'll bet that a thermostat could be reversed engineered onto it.
--
Jim in NC

No, I did not think to specifically look for a thermostat in the
cooling system when I did the installation (so, following the standard
unwritten rules of Usenet, everyone is now free to insult my
intelligence, question my judgment, and/or call my mother's virtue into
question. lol.) In any event, I have discussed the situation with
Lockwood and they assure me that nothing is out of the ordinary with
the temp. They said that they barely get 120 deg of water temp on their
Air Cams. The gentleman I spoke to did warn me to make sure that the
minimum oil temp was being maintained. He also mentioned that the
chatter may very well be a result of carbs that are out of sync. That
was on my "to-do" list already so I'm hopeful that syncing the carbs
will take care of the matter.