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TR2/3/3A Spark plug inspection

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K

karls59tr

Obi Wan
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Looking at the plugs I have a nice tan colour on the electrodes, which is good, but the "threaded part" of the plugs are covered in dry black carbon? Is this something to be concerned about? Do others see the carbon on their plug threaded section or is it reasonably clean? I don't think it's running rich as the electrodes look good. I have heard that TR3s tend to load the plugs with carbon when idling but it just burns off when driving? I believe the choke is returning properly. Would I be further ahead to try a hotter plug or leave things as they are?
 
Your description sounds like what you want to see and what I have seen on a properly tuned engine.

I suspect modern fuel yields something other than the traditional tan color at the body of the plugs.
 
The threads don't seal. Spark plugs have either a metal sealing washer or a beveled surface that seals against the head, so the threads are actually within the combustion chamber and get the mixture forced into them on compression. They are much cooler than the plug tip, so I suspect that's why you are getting carbon there. Just a guess, however.

In any case, I can see no way that it would affect the plug's operation. You have plenty of metal-to-metal contact area on the plug threads, more than enough to get full voltage at the plug tip.
 
Sarastro said:
The threads don't seal. Spark plugs have either a metal sealing washer or a beveled surface that seals against the head, so the threads are actually within the combustion chamber and get the mixture forced into them on compression. They are much cooler than the plug tip, so I suspect that's why you are getting carbon there. Just a guess, however.

In any case, I can see no way that it would affect the plug's operation. You have plenty of metal-to-metal contact area on the plug threads, more than enough to get full voltage at the plug tip.
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I see what you are saying. Actually the carbon powder was just on the top ring of the threaded area ....that's probably normal seeing as how the electrode is tan coloured. (y)(y)
 
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