Non Problem? (Pmag Question)

[Toobuilder]

I have a little more than a year and about 150 trouble free hours on the dual Pmags on the -8. Last weekend I changed the oil and also decided to install a whole new set of NGK plugs. The old ones looked great, but at $18 bucks for a whole set, I change them out every year. Ground run up is normal, with only the EGT rise to indicate I'm running on left or right. Test flight is normal as well, as a mag check at 100 ROP produces no discernible difference in power in the climb (again, only an EGT rise). Top of climb, and my usual 50 LOP cruise setting is completely normal. So far so good.

Where it goes off the rails is when I try a final mag check in the 50 LOP condition. Selecting the right mag only (which runs ALL the bottom plugs) causes the engine to fall on its face. It still runs, but is clearly not happy. Selection of the other mag (top plugs) all is well (slight EGT change). I found that I can richen up the mixture and the "problem child" (RH Pmag) starts to behave normally. To be thorough, I reinstalled the old plugs and was able to duplicate the condition.

So my problem is that I'm not sure I've ever done the mag check in LOP cruise before, so I don't know if this is a new issue (or ANY issue, for that matter). Since all indications are otherwise normal, and I can bring the errant ignition back into normal ops with the mixture, I suspect that the difference is tied to the combustion chamber of the Lycoming engine.

Is there anyone out there running the "all top, and all bottom" split in their ignition, and have you run across the same issue as I have?

Thanks!

[N941WR]

Check your PM's.

[Gash]

I'm really curious about this too. Could you please not PM your response, as I would like to benefit from the discussion as well. Thank you very much.

[Epepperman]

The PM's are sent to avoid ANY content that may be hazardous to sales
Or show there may be an issue

[Toobuilder]

...or because its just easier to hash it out on the phone...

Anyway, considering the engine would not run LOP with two "good" Bendix magnetos (if there is such a thing ...), I'm a long way from throwing stones at a single PMag for not picking up the slack. Lighting off a super lean mixture takes a very healthy spark, after all.

[erich weaver]

Originally Posted by Epepperman

The PM's are sent to avoid ANY content that may be hazardous to sales
Or show there may be an issue

Well, the cat is out of the bag. All of us who have ever sent a PM have been exposed

[Gash]

Which is worse, hazardous to sales or hazardous to safety? I'm not trying to be cute with this question...just sincerely interested in making my system as reliable as possible by learning about everyone's experiences. Thank you.

[MontanaMike]

Let's see, Fifty degrees Lean Of Peak, shut off 1/2 my ignition, induce roughness. What a surprise.

Why don't you try that again and enrich the mixture, then report back.

Mike Bauer
N918MB RV6 O-360 Dual Pmags

[Toobuilder]

I have not had the discussion yet, but I'm not ready to think this is a safety issue at all. After all, single ignition while LOP is hardly normal ops.

...But if you do mag checks like this, AND run PMags split top\bottom, please speak up.

[Toobuilder]

Originally Posted by MontanaMike

Let's see, Fifty degrees Lean Of Peak, shut off 1/2 my ignition, induce roughness. What a surprise.

Why don't you try that again and enrich the mixture, then report back.

Mike Bauer
N918MB RV6 O-360 Dual Pmags

Please read post #1 again...

My question is not THAT it gets rough... (Expected). It is why one ignition takes the load as a single, while the other does not. My theory is that it has to do with the proximity of one plug to the intake port compared to the other. I'm looking for others to share their experience so that I can rule out my ignitions.