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From: "Al Gietzen" <ALVentures@cox.net>
To: "'Rotary motors in aircraft'" <flyrotary@lancaironline.net>
Subject: SAG - Spark plugs
Date: Tue, 7 Jul 2009 17:57:20 -0800
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In-Reply-To: <list-3748446@logan.com>

Leaded fuel will also result in more rapid erosion of the electrodes.
Remember when you burned leaded fuel in your car and you had to replace =
the
plugs about every 5000 miles.  On unleaded they'll go 35,000.  Although =
in
this case you'd think Steve's plugs shouldn't look worse than Ed's.

I run NGK B9EGV in my 20B.  They have a fine wire center electrode.   I =
like
the performance they give, but after about 35-40 hours that center =
electrode
is eroded some and the gap is getting bigger - that using mogas.  On a =
trip
last year where I burned a tank of 100LL (about 45 gals) the plugs =
looked
about the same after 15-20 hours.  They are less than $5 ea from Rock =
Auto,
so I change them at about 40 hours.

The appearance of plugs can fool you.  I noted a couple of months back =
that
the EGT spread at lean cruise was about 75F.  I had adjusted the EC2 at =
some
point, but thought maybe I did it at different mixture.  I changed the =
plugs
prior to departing on the aborted flight to TX, and visually examined =
each
old one.  They all looked the same. One of the things I set out to do =
during
that first hour of flight was rebalance the mixture to get the EGTs =
close
together.  After leveling at cruise and leaning out, checking the EGTs
showed the three to be within less than 20F of one another.  Had to be =
the
change in plugs.

Al G


-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of sboese
Sent: Tuesday, July 07, 2009 1:05 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Emailing: rotor 2 leading, rotor 2 leading b

Ed,

Here are two pictures of a plug removed after 15 hours of use, half with
100LL.  All the plugs look very similar.  Does this plug look typical to =
you
and satisfy your definition of "no discernable wear"?  I'm just trying =
to
satisfy myself that I'm not seeing something anomolous.

Steve Boese