Oily Bottom Plug

RyanB

RyanB

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Mechanic rotated and cleaned plugs after oil change and found the #2 lower plug to be a bit oily. It had not been fouled or causing rough running or bad mag checks. I never would’ve known had he not have discovered from pulling the plugs. He borescoped the cylinder and could see that the bottom of the cylinder wall was oily.

Given that it hasn’t been causing an issue, he said that he wouldn’t worry with it and just monitor going forward.

The benefit of this forum is getting some secondhand opinions. Is this likely to be the start of something more progressive? What would you do if this was discovered - keep flying it or go ahead and pull the cylinder?
 
Keep flying it. eventually it will get worse and then deal with it.My old motor did that for 500 hours until I changed the motor. I had to clean the plug every 75 hours or so. I could feel it when flying. Just not as smooth when it started to get too oily. Never noticed much power loss.
 
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Post Flight mag checks will alert you.
 
Agree with Gary Ward and Magman. Plus exchange plugs top to bottom with your oil changes. That burns off the oil, and prevents premature performance problems. Stock up on copper plug gaskets, and you do have a torque wrench?
 
You might want to check if you have the hottest acceptable plugs. Many engines allow either a #38 or #40; the latter is hotter and more likely to burn oil off. Also a #37BY, while colder on paper, has a projected nose and is less likely to foul.
 
My comment is based on the fact that you had the jug scoped and found no

scoring . A broken ring would likely also put aluminum and steel in the

screen/ filter.
 
There are various areas that will allow oil to leak into a cylinder and end up on a bottom spark plug. Based on the description I wouldn't worry about it and just keep on flying. Spark plug cleaning and rotation at each oil change would probably be beneficial if you aren't doing it already.
 
I cleaned this plug pretty many times.
IMG_61311.jpg

I annealed the washers about the same many times.
044_11.jpg
 
Gary Ward said:
I cleaned this plug pretty many times.
IMG_61311.jpg

I annealed the washers about the same many times.
044_11.jpg
Click to expand...
Eek! Luckily this one didn’t look nearly in that shape. Time will tell!
 
Let'sgoflying! said:
I think that is quenching.
Annealing; is that not slow, air-cooling?
Click to expand...
Copper doesn't behave like steel. Neither does aluminum, for that matter. Quenching hot steel will harden it, if it has enough carbon in it. Letting it cool slowly anneals it. Quenching hot copper or aluminum anneals it. Letting it cool slowly will result in somewhat more hardness, and aluminum, depending on alloy, can continue to harden with age. Both of them harden when they're cold-worked, so the copper hardens when the sparkplug is torqued.
 
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