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Rusty barrel on spark plugs ?

Italiancowboy

Active Member
So during annual we found the exterior of the barrels of the spark plugs on bottom cylinders 1,3,5 (O-540) to be rusty (see photo)
But all other 9 plugs are fine (see photo)
No issues with the plug, normal wear, firing fine.
Engine runs fine

Anyone have a guess on what’s happening?
Why only plugs on lower cylinders on one side ?

Besides ugly, I worry that the corrosion can eventually make them hard to remove.
 

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Do those cylinders run hotter? Sometimes excess heat will promote corrosion of the steel like exhaust headers on a car for example. Carburization…but that’s takes a good amount of heat.
 
Plug corrosion.....

So during annual we found the exterior of the barrels of the spark plugs on bottom cylinders 1,3,5 (O-540) to be rusty (see photo) But all other 9 plugs are fine (see photo) No issues with the plug, normal wear, firing fine. Engine runs fine

Anyone have a guess on what’s happening?
Why only plugs on lower cylinders on one side ?

Besides ugly, I worry that the corrosion can eventually make them hard to remove.

Well, that is just bizarre! That has to be seeding from somewhere else. It looks like the fins on the cylinder have some similar residue on them. Am I seeing that? Do the cylinder fins check out otherwise?

Tempest plugs are nickel-plated. Besides looking cool on the exposed cylinders of the J-3, they might be, in this case, more resistant to corrosion....or whatever that is....:confused:

I hope you removed them and at least sanded them down. I don't think they would be difficult to remove unless the corrosion extends down the barrel into the faceted part of the plug.... (insert shrug emoji...) Yeah, I'd replace those even though they are functioning well. Just when you think you've seen everything..........:confused::p
 
Did you buy all 12 plugs new? Is it possible the rusted ones are from a different package, different brand or even counterfeit? That’s odd…
 
Thanks for the spitballing but most “guesses” wouldn’t explain why these 3 and not the other 9
But inquiries to the OEM is a good suggestion
 
I've seen Champions and Tempest plugs do this also. The only common threads are the airplanes are stored in damp hangars, few months in between flights. They can be cleaned up with a wire wheel and painted silver.
 
Just so you know

Alone it won't solve an issue; however, I'd consider putting one of the "good" plugs in the location that had the worst corrosion. At least in time you'd have a better idea of environmental effects versus a product quality issue.
 
Down for annual so I’ll swap locations as usual then keep track of them

I did fly through some rain last trip but would have thought the heat inside and around the engine would have dried it out.

And again, I keep coming back to “why just these 3?” When the other 9 show very little surface rust.
 
So I sent photos to Tempest rep and he said it’s rare but he has seen the plating fail on some plugs (Champions too)

Said if I sent them to him he’d replace for free.
 
I've noticed that plugs on the upper side of the cylinders suffer the same corrosion as yours. I believe it to be caused by bugs impinging on the plugs and the resulting acidity damaging the nickel plating. I notice it occurs to the greatest extent on the top forward plugs on my four cylinder. It doesn't seem to affect how the plugs perform so I rotate the plug locations at condition inspection and move on
 
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