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FOULED PLUG and IT PAYS TO LOOK AROUND ANTIME THE COWLING IS OFF

chrispratt

Well Known Member
If you’ve never seen a fouled spark plug, this is an example of what one looks like. Note on the right side of the photo the bridged gap between anode and cathode effectively shorting out the plug. On mag check during run-up there was a drop of about 300 rpm followed by a backfire. This is an REM38E used on a standard magneto system and carbureted O-360-A1A. You can also see some carbon buildup on the plug walls in the background. I guess I need to floss my plugs more often :D Ya think I need to lean a bit more? Sure ruined my plans for the day.

BTW the plug had about 230 hours on it so it was just about due to be changed anyway along with the other 7 (I change my plugs at 250 hours).



On the positive side, while changing the plug I also discovered one of the connecting wires from my Unison Shower of Sparks was not in original condition (see below). Don’t know how this gap between connector and shielding happened; looks like I must have snagged it at some point and put a strain on the wire. A new Faston connector was soon substituted.

That’s why it pays to look around anytime the cowling is off.



Chris
 
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Looks to me like some kind of automotive wire was used and the insulation shrunk back. Rip it out and start over :D
 
That may be, Walt. That's the wire that came with the original unit and being a rookie builder at the time (about 14 years ago) I used what the OEM sent. I replaced it with Tefzel wire.
 
Happened to me too..

Same thing just happened to me last week, but I had a cracked insulator that made it even worse. I was accused of "making Popcorn" during run-up the popping was so loud! Same exact plug type.
 
Plugs

I have ran NGK auto plugs for last 100 hours on one of my slick mags gapped at out of the box .025 has worked very well and cost $2.30 each don't know how to post pics but if anyone wants to know how I converted wire to auto send me a PM.
 
That sort of fouling is good reason to change to the REM37BY plugs with extended tips -

CH_REM37BY.jpg


Should be good and approved in all of our engines, but you can check here -

https://www.lycoming.com/sites/default/files/SI1042AC Approved Spark Plugs.pdf
 
Fouled Plugs

I have had trouble with lead-fouled REM-38E massive plugs in both the previous Lycoming O-360A1A in my Piper Comanche and in the present engine until I switched to 4 Tempest fine wires on the bottom and REM-37BY's on the top about two years ago. No problem since, and I can go lean of peak until misfire occurs a lot farther than before.
 
Mags

I have ran NGK auto plugs for last 100 hours on one of my slick mags gapped at out of the box .025 has worked very well and cost $2.30 each don't know how to post pics but if anyone wants to know how I converted wire to auto send me a PM.

I was under the impression the Sparkplug gap was determined by the source of the ignition and the mags were designed for 18 to 20..?
A bigger gap is taxing the coils/etc and will eventually lead to failure.
Food for thought.
 
I was under the impression the Sparkplug gap was determined by the source of the ignition and the mags were designed for 18 to 20..?
A bigger gap is taxing the coils/etc and will eventually lead to failure.
Food for thought.

Yep, me too.
The higher the secondary voltage, coil, plugs and plug wires, the higher the primary voltage, points, condenser, coil. High voltage is always looking for an easier path to ground. Also burns points...
 
Plugs

I'm experimenting and so far temp range looks great and running on bottom with no fowling.Who knows how much more stress is being put on the coil and how much sooner it will fail changing the plugs every 50 hours right now that may make up the difference than running a aircraft plug 500hrs?
Bob
 
I have ran NGK auto plugs for last 100 hours on one of my slick mags gapped at out of the box .025 has worked very well and cost $2.30 each don't know how to post pics but if anyone wants to know how I converted wire to auto send me a PM.

I don't think this setup will be reliable in the long run. The gap is a little large for a magneto, but more importantly the resistance of auto plugs is usually over 5K. That's hard on the magneto components, especially the points.

Vic
 
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