Hi
I have recently baught a XJ6 4.2 Mk1. The former owner says the engine were pinking. I lifted the head because the gasket were blown. And founded that the head were welded in cylinder nr 6 and there were signs of pinking on the piston top.
The gasket were blown due to some of the spacers under the head nuts were to thin.
Now to my question. Could the pinking on number 6 cylinder been caused by fault in the distributor, or could it be by lean mixture caused by air leaking in the inlet manifold?
Hi and welcome!
They have different thicknesses for the lifting brackets and the spark plug lead conduit… as long as the acorn nuts can seat this is fine. If not the stud might have broken or become unseated!
Both of your suggestions are possible though.
Light erosion on the piston is almost normal, can you explain ‚welded‘?
Are the plugs identical? I‘m sure it will run well again if you reassemble it unless it is tired overall.
Hi Jan and again welcome, was there any evidence of a failure of the inlet manifold gasket on number 6 (the cylinder nearest the radiator for XK engines)
First thanks 
Ohhh, then it’s number 1.
By welded I mean you could se a different colour around the combustion chamber like there have been welded.
No there were no signs of gasket failure.
All plugs were black. The former owner tried to compensate the pinking by give it more fuel. It took about 50 litres per 100 km.
That’s 6 miles per gallon.
You are welcome, can you take a picture and upload it, use the 7 th icon from the left on the tool bar 
Its a common mistake non (or first time) Jag owners make regarding the numbering of the cylinders, you’re not the first and won’t be the last 
Jaguar did comply with convention with the later AJ6/16 engines in the XJ40/X300
Impressive, the worst I have seen was 8 MPG but that was from a Nissan 1500 turbo on the track.
Hmm nice looking repair, what does the piston crown look like?
That head has been seriously planed: you might consider a Cometic gasket, if you want the compression to be close to stock.
That piston has been having a conversation with something!
Might have been severe detonation, it looks like in the spark plug hole. Wow.
These look like 9:1 pistons so if the block is still useable you can go for 8:1 pistons if the head is really that shaved down and still useable. Or get a new engine.
Less likely detonation, and more likely steam erosion.
Severe detonation melts, then destroys pistons, rapidly.
Steam erosion caused by inleaked coolant water?
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Yes…plus20 cooling system leaks!
Hi Jan and welcome. Can I ask were the cylinder head and piston tops badly coked up? Coke hot spots will cause pinging.
Hi and thanks.
No, not spectacularly.
I just found an other distributor.
Technically, coking will cause pre-ignition, which is distinctly different to pinking, but with (generally) less-deleterious effects.