Tracy Crook wrote:
Anderson Ed wrote:
Well Folks, I pulled the NGKB8EV spark plugs this week end on my 13B.
Talk about spark plug devastation - the lead and trail spark plugs on
rotor #2 (furtherest from crank pulley end) were destroyed. Plugs for
rotor #1 showed some wear with the lead plug having the begining of a
small ball on the center electrode, but otherwise looked OK. These plug
have 15hrs flying time on them.
The lead plug for rotor #2 had the center eroded down and the side
electrode eroded back until there was a 3/16" gap. The side electode
also had a ball of metal on its eroded end. The ceramic cone around
the center electrode was cracked and one side was missing. The trail
plug center electrode was eroded 1/8" and its ceramic cone was also
cracked and one side missing.
Clearly, either the ignition over advance or the leaning has elevated
rotor combustion temps beyond the capacity of the plugs to handle. I
hate to think what I may have done to the apex and side seals.
I doubt that any damage was done Ed. I had been flying for about 112 hours
with the advance miss-adjusted to 35 degrees BTDC. The reason I started
checking was an odd sound from the engine when doing top speed runs at
6000 - 6200 rpm. I can't describe the sound (it was a pretty subtle change
from normal) but it was accompanied by a slight drop in rpm. I am fairly
certain this was the onset of detonation. Full throttle at high speed is
the only time this would occur. I could climb at full throttle (5000 -
5150 rpm) indefinitely with no problem. Of course I did finally burn up the
plugs as I described in my newsletter but still didn't associate the plug
problem with advanced timing. It was several weeks later that I found the
timing off.
I carefully inspected the apex seals (through the exhaust ports) and they
looked perfect. (No sign of carbon sticking in the grooves after 800 hours
BTW) Compression checked as good as it was 4 1/2 years ago. Actually, I
am quite amazed at the abuse this engine has taken with no apparent damage.
I flew it to Oshkosh & back that first year with a blown front cover oil
passage O-ring and the oil pressure running less than half of normal at 30 -
37 psi. The engine has not been apart (other than the front cover) during
the 800+ hours of operation.
Tracy Crook rws@altavista.net
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