Could be with the skimming of block and head, new stretched studs (not fully bottom in block) the gasket does not get clamped sufficiently.
You can measure gap with out washer installed, just go to two washers or use ARP 12 point nut.
My choice at this stage, would be to clean stud holes in block and go with ARP nut and washer. Admire your persistence !!! Hook 18" brass tube to a shop vac.; and 14 in craftsman 1/4 extension, with tap forced into 9/32 socket.
Rgds
David

 

That is all good advice.

I did clean out the threads in the block with the engine dismantled and the core plugs out, so access was easy. Next time, I will use a tap on an extension like you suggest - I have alread modified a 1/4" extension bar to fit down through the coolant passages (I had to grind it down a bit to make it slim enough), and will do as you suggest with the vacuum cleaner to make sure all the debris is removed.

I have checked that the head nuts do not bottom out on the threads, and will do so again with the new set when I fit them.

Last time I torqued the studs to 27 lbf before fitting the head, as I found advice somewhere on the forum to do this. Then the head nuts to 52 lbf first, let sit overnight then retorque to 54 lbf next day (also following forum advice elsewhere). Any comments on that?

I think the main problem that remains is the poor fit of the head gaskets in relation to the bores and the slots. There is so little clamping area anyway between the slots and bores, that if the gasket is even slightly off position, then it has little chance of success.

When I get the Payen gasket I will compare it with the last but one gasket I used (which I kept for reference) and see if there are noticable differences. It will be a few weeks away though as I am away on a work assignment.

 

"Last time I torqued the studs to 27 lbf before fitting the head, as I found advice somewhere on the forum to do this. Then the head nuts to 52 lbf first, let sit overnight then retorque to 54 lbf next day (also following forum advice elsewhere). Any comments on that?

Those are same numbers I found on research and have done on two Cylinder Head re-installs.
Rgds
David

 

Since you have a few weeks, check out this head gasket... It has various thicknesses for skimmed heads. I have not used this company, but have heard good comments.https://www.cometic.com/applications/automotive/jaguar/xj6
Rgds
David

 

I had a message from David Manners Group, from whom I also bought 2 head gaskets, that the Payen version is identical in layout to the pattern part they supply.

Therefore, I have done as David suggests and contacted Cometic (in UK not in USA though).

They are making me one (with 6 week lead time). Very expensive by comparison though. It is £160 including VAT and post. However, if that resolves my problem, it will be money well spent.

So roll on September and I'll be able to try agian.

 

Well, you my read this before your September date.

I have a flex tool with a small magnet at the end. it is skinny. get one. dip it into the threaded hoes after you clean them with a tap. that should attract the swarf for easy emoval.

Good luck. Gluck!! suerte....

 

End of the Saga

I didn’t get on very well with Cometic. After providing them with all the information on my engine (car model year, engine size, engine number etc etc) they took 6 weeks to make and send the gasket to mu UK address. That was fine as I was spending September there anyway. However, when it arrived it was for a 2.9L XJ40, not a 4.2L XJ6 series 3, so I had to return it. A further 6 weeks later they informed me they had the correct gasket but then wanted an extra £100 to ship it to Thailand on top of the £160 I had already paid. I had to cancel the order.

In the meantime, SNGB sent me a Free-of-Charge genuine Payen gasket set. On comparing the new Payen head gasket with the last unbranded one I had taken off, there was a big difference in the spacing of the firing rings, with about 2mm difference between the two gaskets at cylinder 1 if both aligned at cylinder 6. Also, all the firing rings had a slightly smaller internal diameter i.e. potentially more sealing area (see pics with unbranded gasket laid on top of Payen gasket).





So I removed the head again, cleaned up, replaced all the studs again in case of thread stretch (being careful to ensure all the stud holes in the base of the block were clean and clear of debris / water and that studs screwed down correctly in the correct places) then fitted the new Payen gasket and torqued down with new dome nuts. This time I used fresh water / antifreeze mix and added a can of K-Seal which I had hand-carried back from UK.

This seems to have solved the problem and the car is not using coolant any more.

Many thanks to all who contribited to this discussion and helped me resolve the problem. I think perhaps those pattern part unbranded gaskets would work OK on a non-slotted-type block, but the minimal surface area on the slotted block makes them unsuitable.

 

Back in the day, Jaguar recommended Barr's Leaks be added when changing the coolant. K-seal is probably better.