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  #11  
Old 05-24-2019, 10:59 AM
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GalinHdz GalinHdz is offline
 
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Quote:
Originally Posted by SmilingJack View Post
I replace my auto plugs at every condition inspection.
I do the exact same thing.

Quote:
Originally Posted by N941WR View Post
For the price, it is cheap insurance just to replace them once a year.
I agree
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  #12  
Old 05-24-2019, 11:05 AM
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Quote:
Originally Posted by N941WR View Post
Correct and that is exactly what our Professor found. However, it was the insulation that was starting to fail.

That's why I recommend people don't use high dollar iridium plugs, the metal part isn't the issue.

For the price, it is cheap insurance just to replace them once a year.
Let's back up a moment Bill.

The professor found reduced resistance. Where was this reduced resistance...the center electrode ceramic, or the ceramic body?
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  #13  
Old 05-24-2019, 11:47 AM
Norman CYYJ Norman CYYJ is offline
 
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What's wrong with replacing them when required. That's what is done with regular aircraft spark plugs.
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  #14  
Old 05-24-2019, 12:01 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by DanH View Post
Let's back up a moment Bill.

The professor found reduced resistance. Where was this reduced resistance...the center electrode ceramic, or the ceramic body?
Dan,

I would have to dig in my old computer to find his report (and we are leaving for the weekend) to answer if it is the center insulator or the external one.

Here is a description of the behavior that prompted us to send a set off:

The P-mags report the current flow the EIC. A shorted or fouled plug would display as a maximum scale reading (100). A broken or open plug lead would display no bar graph (0). (We set the reported values to a 100 point scale for display purposes.)

When new NGK BR8ES plugs are installed, we typically see a value between 70 and 80. As they accumulate flight time, that value drops off and readings of 40 are not unheard of when 100+/- hours are recorded.

Obviously the plugs resistance is going up, limiting current flow. What I haven't done, is to Ohm used plugs and compared them to new ones because I believe the EIC reporting function.

The odd part is I could not detect any change in engine performance; either roughness or reduced performance. The only indication I had was what the EIC was reporting. Replace the plugs and the bar graphs to back up.
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  #15  
Old 05-24-2019, 12:14 PM
rv7charlie rv7charlie is offline
 
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Hmmm...'Trust, but verify' (?)

Ever try pulling the cap, removing and re-installing the plug, and rechecking the EI's reading? A simple resistance check, new & after, could be useful data, too.

IIRC, running a 'colder' plug makes conducting tip heat out to the head easier. Would that reduce the heat load in the internal resistor in the plug, extending life?
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  #16  
Old 05-24-2019, 12:23 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by rv7charlie View Post
Hmmm...'Trust, but verify' (?)

Ever try pulling the cap, removing and re-installing the plug, and rechecking the EI's reading? A simple resistance check, new & after, could be useful data, too.

IIRC, running a 'colder' plug makes conducting tip heat out to the head easier. Would that reduce the heat load in the internal resistor in the plug, extending life?
Yep, done that with regard to pulling and resetting the plug wires but have not pulled a plug to check it's resistance, as I said. No change was noticed.

Also, heat doesn't seem to impact the readings. The numbers do move around but the general trend is down. Meaning that one one flight, from startup to shutdown, the numbers are fairly consistent. Over multiple flights, the numbers trend downwards.

I have not hit the cylinder head with a laser thermometer but I imagine that once the plugs are up to temperature, which might happen slightly faster than the head, the readings are pretty stable.
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Last edited by N941WR : 05-24-2019 at 12:28 PM.
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  #17  
Old 05-24-2019, 01:34 PM
rv7charlie rv7charlie is offline
 
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I was thinking more about how fast the internal resistor degrades ('cold' resistance rises) ; not whether heat affects real-time readings. Does NGK publish min/max resistance specs for its plugs, like a/c plugs?
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  #18  
Old 05-24-2019, 01:34 PM
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Quote:
Originally Posted by N941WR View Post
I would have to dig in my old computer to find his report (and we are leaving for the weekend) to answer if it is the center insulator or the external one.
Have fun! It will wait.

Quote:
Here is a description of the behavior that prompted us to send a set off:

The P-mags report the current flow the EIC. A shorted or fouled plug would display as a maximum scale reading (100). A broken or open plug lead would display no bar graph (0). (We set the reported values to a 100 point scale for display purposes.)

When new NGK BR8ES plugs are installed, we typically see a value between 70 and 80. As they accumulate flight time, that value drops off and readings of 40 are not unheard of when 100+/- hours are recorded.

Obviously the plugs resistance is going up, limiting current flow. What I haven't done, is to Ohm used plugs and compared them to new ones because I believe the EIC reporting function.

The odd part is I could not detect any change in engine performance; either roughness or reduced performance. The only indication I had was what the EIC was reporting. Replace the plugs and the bar graphs to back up.
Hmmm. That's the functional opposite of what you previously wrote, which was...

Quote:
We sent a bunch off to a PHd professor to look at and he found the ceramic insulators were starting to deteriorate.
and

Quote:
However, it was the insulation that was starting to fail.
I'll wait for the report.
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  #19  
Old 05-24-2019, 02:06 PM
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rv6ejguy rv6ejguy is offline
 
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I pulled the factory original NGKs out of my 2002 BMW a few years back with 120,000 km on them. Still looked almost like new. Resistance measured very close to the new ones I put in to replace them. This is a coil on plug setup where the plugs are trapped deep down inside the valve cover with no air circulation at all. This car has been tracked and driven hard its whole life. I've owned it since new.

I've installed thousands of NGK plugs so far in my lifetime and seen only one bad resistor which was on a new plug, out of the box. Other people's experiences may be different but be sure you are not using counterfeit plugs. Those are circulating from cheap sources.

I'm not sure about mags and other EIs but our stuff will reliably fire plugs in a naturally aspirated engine with completely missing ground electrodes. A little bit of plug wear is of no concern with SDS so I don't think you need to be tossing them at 100 hours.

Are other folks on here finding resistors going bad in NGK plugs?
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Last edited by rv6ejguy : 05-24-2019 at 03:30 PM.
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  #20  
Old 05-24-2019, 02:19 PM
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plehrke plehrke is offline
 
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Quote:
Originally Posted by N941WR View Post

The P-mags report the current flow the EIC. A shorted or fouled plug would display as a maximum scale reading (100). A broken or open plug lead would display no bar graph (0). (We set the reported values to a 100 point scale for display purposes.)
What is EIC?
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