REFLECTOR: Denso X27GPR-U spark plug problem

aminetech at bluefrog.com aminetech at bluefrog.com
Mon Nov 1 12:35:56 CDT 2010


Alex,  That sounds possible.  I spoke with Klaus this morning and he thinks it's detonation.  I'm going to check that first, by remaining full rich at low altitude and check in 10 hours.

John

--- velocity_pilot at verizon.net wrote:

From: "Alex Balic" <velocity_pilot at verizon.net>
To: "'Velocity Aircraft Owners and Builders list'" <reflector at tvbf.org>
Subject: Re: REFLECTOR: Denso X27GPR-U spark plug problem
Date: Mon, 01 Nov 2010 10:46:09 -0500

Hi John-
Is it possible that the oil contains some metal that is then deposited on
the plug, oil burns away leaving only the string of metal there? Just a
thought- might be oil related after all- possibly a ring is wearing and the
oil takes the metal up into the combustion chamber.

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of aminetech at bluefrog.com
Sent: Sunday, October 31, 2010 12:10 PM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Denso X27GPR-U spark plug problem

100 hours ago I replaced standard aircraft plugs with Denso X27GPR-U spark
plugs.  They worked great until recently when on 2 occasions I noticed a
faint missing sound right after takeoff.  It went away after a few seconds.
When I inspected the plugs, 5 were in perfect condition.  The gap on the #4
cylinder was completely filled in with a black, layered, flakey material
that resembled rust on severely corroded steel.  Unfortunately I didn't take
a picture of that.  The attached pic is what it looked like after brushing
the plug clean.  As the pic shows, the outer electrode is severely eaten
away.  (I sent this pic to Klaus 10 days ago, but no response) I replaced
with a new plug and the engine ran fine.  After 10 hours the EI ran poorly
during a mag check, so I pulled the #4 plug and found a "string" of material
spanning the electrodes.  (see pic in next email)  I'm sending the pic in
another email as both may be to big to send together.  Two people have told
me it looks like oil fouling, however my oil consumption is normal at 1 qt/4
hrs.  Also, several years ago when I did have high oil consumption (1 qt/hr)
due to 2 broken rings, the plugs did not foul.  Still, with 2 people
suggesting oil, it behooved me to look into it, so I collected the deposits
for testing.  They are magnetic.  I did an ash test which vaporizes all
non-metal materials.  No smoke occurred during the test which indicated
nothing was vaporized.  There was no weight loss which confirms that the
deposit is all metal(s).  During the ash test the material had a dark red
glow which is consistent with iron.  No other colors which would indicate
certain other metals, were present.  So, I'm certain that oil is not a
factor here.  Several years ago I had the same thing happen with a standard
aircraft plug/EI ignition on the #1 cylinder.  One common element between
then and now is that I flew several hours at 2-3000 msl at reduced  power
just prior to the fouling.  This altitude is unusual for me.  I normally fly
7-12k.  At low altitude and full rich the fuel burn is 13-15 gph (depending
on throttle setting).  That seems a lot so I lean it a bit to get 10-12 gph.
Maybe that's a problem, but CHTs aren't affected.  I think I'll try full
rich and see it that helps.  Does anyone else lean at low altitude?  Any
ideas or operating data with Franklin engines will be appreciated.

John


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