My XJC recently presented with a bit of a miss when cold and my immediate thoughts were possibly fouled or dodgy plugs. Replacing the NGKs with some new Champion N11Y’s, all is well and good once again in Jag land.
I did however note that the plugs looked quite different from 1 to 6. Now given that I’ve had the engine fully rebuilt, including the carbs a couple of years ago, with less than 10,000km on that engine, I’m just wondering as to why the difference in appearance of these plugs?
What do the different colours mean and what might be causing this difference from no. 1 plug through to no. 6?
It is interesting that Jaguar numbered the cylinders in their XK engines (3.4L, 3.8L, and 4.2L) from the firewall forward so #6 is at the very front of the car and #1 at the firewall, and they also numbered the cylinders on the 5.3L and 6.0L V12 engines exactly the opposite with cylinders #1A and #1B at the front of the car and #6A and #6B at the firewall.
They supposedly did that, so the story goes, because the engineers that designed the XK engine during wartime were all aircraft engineers …and apparently it is common practice to number cylinders from rear to front on aircraft…
FWIW
PS: What he said above…zzzz One of these days I’ll learn to read the entire thread prior to responding…
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Spot on, John - if you have numbered the cylinders from front to rear…
As Paul says; Jaguar numbered the cylinders from the rear - but your line-up implies that you got that wrong…
However, one cannot exclude the possibility that both are running fat, but an air leak cause one to run to lean. Or that both carbs require some attention - as Bob remarks; three plugs are suspiciously clean. Which may also indicate an air leak…
even though I am quite familiar with Jag engines, I still mark the firewall & or head with a discreet number 1, its very annoying to get things mixed up and easy to do, (it also means I have to do the reverse on other vehicles I work on)
Just for clairifcation. cyl 1 is at the back (bulkhead), and 6 is closest to the radiator. that being said, I would say either a vacuum leak around a the front (4-6) or carbs may need some love.
correct you are! Too many cars to keep track of, yes numbering of cylinders is shown in reverse.