The following is an exchange between Ed and me earlier today. I hope Ed doesn't mind my forwarding it to the list.
For some reason, my replies to the list are unreasonably large and cannot be read (at least by me) in the archives. I hope that I'm not distributing a virus and that creating new messages instead of simply replying works OK.
It has occurred to me that it may be possible to initiate SAG by going to a hotter plug instead of waiting for a used one to malfunction. If I can do this with the engine on the test stand, that may enable studying the SAG phenomenon
with less risk (to me- not necessarily the engine). A starting point may be using stock leading plugs (BUR7EQ) in all four locations.
Steve Boese
Ed and all,
The replacement colder plugs I thought I'd try are:
11524-NGK Spark Plug<br>BR10EIX
Racing @ 9.44
as copied from the order to Racing Beat.
As I mentioned in the talk at Paducah, I tried all sorts of chemical cleaning methods and the lead remained on the insulator. My thought is that the lead may be incorporated into a glass type of phase that
has significantly less thermal conductivity than the alumina insulator. I agree that the fact that the room temperature resistance of the material on the insulator being over 10 raised to the 13th power ohms with the connecting points as close as possible
(about 0.030" apart) does not mean that the material does not become conductive at higher temperatures.
The fact that the EGT drops and the coolant and oil temperatures rise during SAG whereas the EGT rises and the coolant and oil temperatures drop when disabling either the leading or trailing ignition
coil suggests to me that SAG is not a result of the spark plug misfiring.
I have not seen the kind of damage to my spark plugs that the photo of the pre-ignition shows either.
Alternative explanations for the observations are more than welcome and I am willing to try to test these alternatives as much as I am able and encourage others to do the same within the limits of acceptable risk.
I have no personal investment in one theory over another, but am just interested in understanding what is going on.
Steve Boese
From: Ed Anderson [eanderson@carolina.rr.com]
Sent: Thursday, September 30, 2010 11:39 AM
To: Steven W. Boese
Subject: Lead Fouled Plugs
Hi Steve,
Was looking into colder plugs myself and came up on this at the Champion SP site
Lead
fouling can be difficult to diagnose. Although it usually appears as yellowish brown
deposits on the insulator nose, some fuel additives may also cause similar discoloration (and are harmless). Also, a fouled plug can typically be detected with a simple resistance tester,
whereas a lead fouled plug will read within specs (while at room temperature). Also, the ease of
fouling will vary on different engines even with the same lead exposure; this is because lead compounds combine at different temperatures. Those formed at 370-470°C (700-790°F) having the greatest likelihood of causing lead resistance (
fouling)
on a plug.
I thought this was interesting , I know you attempted to measure the resistance of the Lead coating. It appears (if I read this correctly) that while normally (carbon?) fouled plugs will give you a lower resistance reading, it appears
that Lead fouled plugs will give a normal resistance reading at room temperature. So apparently the lead conduction (fouling) must take place at elevated (running ) temperatures. Just thought I would throw it in the hopper {:>).
Here is a photo of what they say a pre-ignition plug looks like - My plugs never looked like that except for the one time during first 60 hours of flight when I inadvertently set the static ignition timing to 45 Deg BTDC. Sagged plugs
never approach this condition in my experience.
Ed
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plug damaged due to Sustained pre-Ignition
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