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Ed,
I've been hearing about SAG periodically. I don't fell like I know all of the details or the finer points of the symptoms, but some brain farts have occurred to me: If as you say it's the plugs getting dirty enough around the porcelain shroud, to lay down a carbon arc (like in a damp distributor cap) I would doubt that trick electrodes would help. Since it's peculiar to rotary engines and is basically unheard of on recips, one might reasonably attribute it to the shrouded plug(s). I'm wondering if SAG can be replicated on the ground. Like if you experienced it on takeoff, can you reasonably expect (after you've recovered) to make it happen on the ground, say during a prolonged high power turn up? I would intuit that since power SAGs but doesn't DISAPPEAR, that it only involves one plug. I would furthermore intuit that it would be the shrouded plug. Is there an accessible primary wire that powers the leading or lagging plugs that might be switched for test purposes. If you could replicate the symptoms by shutting down the leading or trailing plugs I think it would give you some insights into the problem.
If I'm not mistaken, a very "cold" plug in a recip engine will start missing after a relatively short period, and a very "hot" plug can get hot enough to lead to detonation. What if you were to replace your shrouded plugs with plugs about 3 or 4 heat ranges hotter and see how long they last. I can't imagine how a shrouded plug could make a hot spot prominent enough to cause detonation.
Or am I missing something REALLY important here ... Jim S.
Ed Anderson wrote:
No, I'm not certain, Mark,
However, the plugs are not necessary worn out at 20-30 or 100 hours on MoGas
but they must have the center ceramic cleaned of lead or carbon deposits.
Not arguing that platinum and Iridium plugs won't give longer life - just
don't believe they will go significant longer before the SAG hits.
Those that have not yet hit the SAG have a thrill awaiting. The first time
your engine drops in rpm and the EGT drops 300F, you'll likely think some
major problem has occurred. For months I though I had erratic fuel
injectors or some intermittent fuel problem. Tracy is the one that put me
onto the plugs - change to new plugs and the problem ends immediately.
Generally backing off on the power seems to help temporarily and the
condition will go away on its on (after getting your heart beat accelerated)
to recur at ever increasingly frequent intervals. Seems to happened mostly
at high power settings - like on takeoff where you really don't want
anything unusual from the engine. Even though I have had it happen a number
of times, I still have not gotten use to it {:>)
Ed A
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