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