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1. 07:12 PM - Re: low compression on Jabiru engine using AVGAS (Jabiru Chile)
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| Subject: | low compression on Jabiru engine using AVGAS |
Thank you guys for the info and commends. I think the same way that the
AVGAS here could be a problem. I'm still investigating the problem and if I
find something interesting for you, I will post it in this forum again.
Thank you,
Christian
_____
De: owner-jabiruengine-list-server@matronics.com
[mailto:owner-jabiruengine-list-server@matronics.com] En nombre de
BobsV35B@aol.com
Enviado el: Friday, October 22, 2010 12:45 PM
Para: jabiruengine-list@matronics.com
Asunto: Re: JabiruEngine-List: low compression on Jabiru engine using AVGAS
Good Morning Doug,
Your comment is correct as far as it goes.
However, you will note that Jabiru does suggest changing the jets and the
metering rod to get the mixtures desired. The Bing Carburetor does
automatically adjust the mixture due to changes in altitude, but the changes
at high power and at cruise are made by changing the components in the
carburetor to compensate for different RPM on various engine applications.
Christian's problem still may be heavily associated with the 100/130 fuel
that is being used. 100/130 is NOT the same as 100LL. If the 100/130 AVGAS
still has the composition that we in the USA had before 100LL came on the
scene, he is getting an abominable amount of lead in the engine. If it is
running rich at relatively low power settings (below seventy-five percent or
so) lead will be built up on valve stems, spark plugs, and in the ring
lands. No more lead should be used than is absolutely required for the
compression being used.
Higher octane fuel does no good at all in an engine that does not have a
compression ratio requiring it. Getting a high octane rating by using lots
of lead is especially hard on the engine. The more modern USA standard 100
LL has a LOT less lead than does/did 100/130 AVGAS.
Not sure which is available where Christian operates, but lead is bad and
should be avoided wherever possible.
While the fuel used at full takeoff power must be rich enough to have a
suitable octane rating to avoid detonation at that power, no lead at all is
needed at cruise power and operating on the lean side of best power for
cruise is always the best for the engine provided that distribution is
adequate.
Jabiru attempts to get a suitably rich mixture at takeoff power and a
suitably lean mixture at cruise power by selecting appropriate fuel rods and
suitable jetting. The Bing Carburetor works great when it is suitably set
up. Personally, I would prefer to have manual mixture control, but I am
horribly old fashioned. <G>
Happy Skies,
Old Bob
In a message dated 10/22/2010 10:09:01 A.M. Central Daylight Time,
Kayberg@aol.com writes:
Barry,
Do you have significant experience with Jabiru engines? Your comments
would indicate a background in other engines (Ly-Con) which are not the
same as a Jabiru.
For example, the carbs are not leanable, nor is leaning suggested by Jabiru
Further, since the Jab engines have such a low oil volume, your Marvel
Mystery Oil suggestion is not a good one, and might generate a whole other
set of problems.
Doug Koenigsberg
In a message dated 10/20/2010 11:10:11 P.M. Eastern Daylight Time,
flyadive@gmail.com writes:
Christian:
There is a VERY good chance you are experiencing the same problems MANY
engines here in the USA are experiencing while running on 100LL. 100LL is
really not Low Lead at all. It is four times the lead as the old AvGas 80.
Since you are having low compression I would bet that they are experiencing
lead/coke build up in the valve stems.
If the build up goes untreated the valve will stick in the down (open)
position and if the valve - cylinder clearance is an interference fit they
will be spitting out valve parts. AND even if it is not an interference
fit, the compression will go to zero and still again they will be looking
for an emergency field and new engine parts.
The options are:
Use TCP in the fuel to reduce lead build up
LEAN AGGRESSIVELY - ALL THE TIMES -- Even when taxing.
Use AUTO - MoGas or a mixture of MoGas & AvGas. Just keep the octane where
needed.
1 hour flight before every oil change put in one quart of MMO (Marvell
Mystery Oil) - This helps clean the build up.
Now, these suggestion come with the limited information you gave. We don't
know how the engines are being run.
The time between oil changes.
The type of oil being used.
The quality of the gas and at least a dozen more items.
Since you identified that the engines have low compression - Have you
identified where they are leaking from?
Valves or Rings?
Any gasket leaks?
Fill in the blanks on the above questions and I'll try to diagnose.
GOOD LUCK,
Barry
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