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Date: Thu, 23 Jun 2005 00:43:49 -0400
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From: "Christopher Zavatson" <Christopher.Zavatson@udlp.com>
Subject: [LML] Re: Induction air filter
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Walter,

<<We have watched many detonation events--some=20
even heavy detonation events--some for extended periods-without  any=20
ill effects on the piston, cylinder or engine in general.  The danger=20
is these turning into pre-ignition, usually from a damaged spark plug=20
from the detonation.  That can destroy the engine in 30 seconds and=20
while our observations are that detonation doesn't hole a piston,=20
pre-ignition will do it in a heartbeat.>>

Now I'm confused. =20
A few year back my plane was topped off with 20 gallons of fuel that was =
about 95% avgas and 5% Jet A.  I didn't notice anything unusual while =
operating the engine.  6 flight hours later, I and 200 other unlucky =
aircraft owners were informed of the fuel contamination.  Upon removal of =
the cylinders and connecting rods, we found that the rear pistons had been =
almost completely cleaned of all carbon deposits and a new uniform deposit =
layer had started forming.  The front pistons had not been so completely =
cleaned and so the much of the original carbon deposit layer was still =
present.  It had a coarsely pitted appearance.  The exhaust valve seats =
had turned blue.  Also, the babbitt in the connecting rods bearings had =
been smeared against the crank. =20
The diagnosis at the time was detonation.  Do you agree?  The scary part =
is that I couldn't tell anything was amiss.  All indications in terms of =
sound, feel and temperatures were within typical operating ranges, yet it =
caused the engine to be scrapped.  I imagine the plugs were not damaged as =
they continued to fly for six hours without any sign of trouble.  I =
probably had 3 hours on a 2.5% blend of Jet A and 3 more on something much =
more dilute.  The engine was a completely stock Lyc. 0-360A1A with 300 =
hours since new.  I was left with the impression that a little (not =
noticeable) detonation over a long period of time (a few hours) will =
destroy an engine. =20

In the affected group, turbo charged engines, modified engines (hi-comp =
pistons etc.) and those receiving the highest concentrations of Jet-A did =
almost come apart at the seams leading to a number of emergency landings.

Chris Zavatson
N91CZ + engine #2
360 std