Following on from Remi's post, it might be worth following the recent blog
on the Rotax Owners website. A Rotax 912 owner suffered a partial fuel
blockage to one carb that only showed itself under high power conditions-
and then only intermittently. In your case, if you have a partial fuel flow
problem to one carb, reducing fuel flow by changing power settings could
make the symptoms disappear.
Worth checking?
Regards
Brian Davies
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Remi Guerner
Sent: 19 October 2011 10:02
Subject: Europa-List: Re: Heavy In-flight Vibration Riddle /The Solution
/The Winner(
--> <air.guerner@orange.fr>
Hi Raimo,
As an engineer who has been working two decades for a spark plug company, I
want to add a few thoughts about your engine problem:
A misfiring spark plug, cannot cause detonation.
A single misfiring spark plug on one cylinder cannot cause the high level of
vibration you have experienced.
There are only two cases where a spark plug can cause detonation: the first
one is if you are using a spark plug with a too hot heat rating. In this
case, the nose core and the center electrode of the spark plug becomes red
hot and ignite the fuel mixture even without a spark. The second case is
when the spark plug is not torqued enough, becomes loose so that the heat
transfer from the shell to the cylinder head is limited, causing the spark
plug to become very hot. Both cases will cause preignition and possible
detonation.
I assume you were using the right spark plug type and that your blue spark
plug was found to be tighten correctly. So in my opinion, the very hot blue
spark plug you got was not the cause but the consequence of another
phenomenon, probably preignition and/or detonation, caused by something
else.
The two main causes of detonation are: a too lean mixture and a too low
octane fuel. This is were I would direct my investigation.
Preignition and detonation may seriously damage all combustion chamber parts
such as piston, rings, and valves.
After such a problem I would ground the aircraft until the root cause is
found, and I would carefully check the above parts for damage. Before
removing the cylinder, I would perform a compression check and a boroscope
inspection of the combustion chamber.
Hope that helps.
Remi Guerner
F-PGKL
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