P-Mag auto plug life expectancy

[N941WR]

I’m throwing this out there to see if others have experienced similar issues.

As the manufacture of the EICommander I answer a lot of questions (both on and off line) regarding issues with P-mags.

A month before my Condition Inspection was due my EICommander started giving me some odd readings regarding the health of my ignition. However, the P-mags were timed correctly, they were advancing in unison, they were both running the same configuration, the CHT’s & EGT’s were “normal”, and the engine just felt fine.

After going through every test, connection, and whatnot, I decided to change out the NGK BR8ES spark plugs with a new set. What the heck, I typically change them at every Condition Inspection, so doing it a month early was no big deal. Besides, they had about 105 hours on them. (I know, it was a slow year for me.)

The new plugs were gapped for .032 and installed. The old plugs were checked and the gaps were right at .032 and they looked fine. I could find no issues of any kind.

After changing them out, the EICommander reported all was fine.

Brad at Emag Ignitions, told me “There is some anecdotal evidence” that the plugs go bad at around 100 hours.

In discussing this with my partner in the EICommander, who flies a rotary powered RV-6A, I was sent this little gem:

Bill, having read about the ignition problem you refer to, I may have something to contribute.

As you know, I and most of the folks who fly rotary engine powered aircraft use regular automobile spark plugs. Most folks fly using auto fuel, but I and a few others fly almost entirely using 100LL av gas. What I and others have discovered is that after approx 100 hrs (it varies) on Av gas, the engine develops what we call "SAG" (Sparkplug Attention Getter).

The engine will take on a different note, rpm will drop and (in the early stages) after a couple of minutes things return to normal. The interval and duration of the SAG continues to increase - this can be quite disconcerting and lead folks off on wild goose chases trying to fix fuel and other problems.

We had one technical analysis which included cutting open the offending plugs - it appears that after 100-120 hrs running on Av gas the lead in the fuel gets deposited on the ceramic cone, also it appears that the continuous (hour after hour) of high engine rpm stress internal bonding of the auto spark plug components and leads to deteriorating spark performance. The only cure that we have found thus far is to replace the auto plugs.

So any time a new rotary flyer reports those types of symptoms, we tell them to change their sparkplugs.

Now without use of 100LL, those folks using auto gas generally get a several hundred hours or more - this SAG pertains to use of auto plugs with 100lL

FWIW

Ed

This is just food for thought. At less than $20 for a set of eight plugs, I now replace them all at 100 hours. Because of the cost involved, I don’t even bother with platinum plugs.

[miyu1975]

Thanks Bill. Just so happens mine are right at 100 hrs and my cowl is off for painting...guess I will go ahead a put new plugs in too.

[Toobuilder]

Bill,

Do you check resistance of your new plugs before install, and did you check the "old" plugs? I've found all the new ones to be right around 4,500 ohms.

Longest I went was about 120 hours, but they were performing well- I simply replaced them because... Well they're cheap!

[N941WR]

Good call Michael.

I just checked four of the eight plugs I removed and three of the four were between 4,200 and 4,3000 with one up at 4,500 ohms.

[MS19087]

Hi Bill - You may or may not have an opinion here . . . I'm running dual P-mags and am preparing for my condition inspection - just at 120 hrs on the top plugs - half that on the bottom since I added second P-Mag later. I currently am using the BR8EIX (expensive!) plugs. Any reason not to go with the cheaper BR8ES plugs?

Thanks!

[Toobuilder]

Mark, I know you asked Bill, but let my throw my opinion out there.

The primary benefit to the exotic plugs is consistent performance with low maintenance over a long life. New car drivers would never stand for a plug change at every "tuneup" like back in the 60's. these plugs are used to make cars "maintenance free"...

That said, I'd keep them in there as long as they are performing. Do a visual inspection and ohm check every year, and call it good. JMHO.

[dealfair]

Thanks mucho Bill. I'm a little over 100 hrs & burning 100LL. Have the plugs & cowl is off. Going to do the swap, very timely. Yes, at the lower expense and given the time, seems wise to go with the lesser plug.
Really appreciate the post!!

Cheers,

[dealfair]

Originally Posted by Toobuilder

Mark, I know you asked Bill, but let my throw my opinion out there.

The primary benefit to the exotic plugs is consistent performance with low maintenance over a long life. New car drivers would never stand for a plug change at every "tuneup" like back in the 60's. these plugs are used to make cars "maintenance free"...

That said, I'd keep them in there as long as they are performing. Do a visual inspection and ohm check every year, and call it good. JMHO.

Darn Mike, was typing my post then read this. Yeah, why not test & check?? Will do.

Thanks,

[rocketbob]

If 100LL were so detrimental to a spark plug's life then most massive electrode plugs would not last long. And this is not the case since I've seen them last over 1000 hours many airplanes including mine.

I think the BR8x plugs are too hot for a Lycoming.

On EI I run BR9ES plugs which I rarely replaced on condition inspections because I could see no visible wear. I easily got 4-500 hours on them and just replaced them even though they didn't need to be replaced

[MarkW]

Since I am not flying yet I sure can't argue with R Bob but I sure would be using the old color/condition method to find the correct plug.
I also can't imagine having to replace a properly choosen plug every 100 hours with or without lead.
NGK has an excellent website for that.
http://www.ngksparkplugs.com/tech_su...x.asp?mode=nml