Spark Plug Colouration

[james.ed]

pulled out my spark plugs today whilst giving the engine a once over. found that three of the four are a semi burnt redish colour (but not to bad) and one has more burning and a green / whitish residue around the screw. my head gasket had blown earlier this year and i think that's the cylinder the greening is on. i'm no mechanic but i have read that changes in colour generally mean something so my question is.. is this a sign i need to adjust the mix and if so.. how!

aside from this the engine runs great and will cruise at forty and make seventy / seventy five if she's got the room to make it there.

[rayofleamington]

the green is likely to be from contamination - copper (e.g. headgasket) would give blue, but maybe that's helped it go green?

Are you using a fuel additive?

[bmcecosse]

The colour of the inner ceramic insulator gives an indication of the mixture, although only reliable if checked immediately after a good run - not after messing about in traffic.

[simmitc]

Which end of the thread id the discolouration? If it's near the hex base then it could be stray coolant or similar just collected in the recess where the plug sits and then the water evaporated. If it's inside the cylinder then it opens a lot of questions. Could you post a picture of the plug?

[james.ed]

thanks for the help. I'll try and take a snap tomorrow if i have time.

The greenish powder looks like some kind of oxidization but it was all on the outside (the hex and lead) end of the plug so something could have collected in the little well around the thread before turning into the mysterious powder. As for the plugs.. i checked the after a quick run to get the oil hot for draining, so perhaps nothing useful is to be read by them. for good measure i've got some new sparks installed.

slightly off topic.. but what gap should the spark plugs be set to. everything seems to run great but i haven't adjusted them at all (they're straight from the box champions).

[james.ed]

also.. no fuel additives. I'm an unleaded conversion.

[mike.perry]

0.025in

[james.ed]

thanks.. gaps set properly (they we're nearly correct anyway). I've double checked the plugs i've removed and the green / blue is well on the exterior of the plug so it must have been a spill of something. whilst checking the gap i noticed the new plugs are already have a dusting of soot. I'm guessing this is because the engines not been run for long (so not becoming hot enough) and its been cold so the chokes used to start her. I'll keep an eye out in the next week and check them again after a nice country run.