Hi all - I have coveted getting a XJ12C (5.3) and indeed bought a wreck 30 years ago to restore but was beyond me at the time - still have its engine though.
Locally XJ12Cs are basically not available (there is one but is the wrong colour and very expensive) but XJ6Cs come up regularly. Given I have an engine and all V12 instruments etc would there be any real issues in pulling out the 6 cylinder engine and replacing it with the 12 cylinder - other than engines were there any other differences between the 6 and 12 versions of the Coupe.
As engine swaps go I found this to be straightforward. In my case I had the huge advantage of having a V12 donor car. Every V12-specific part was culled for use on the recipient car. Cables, mounts, entire wiring harness, ECU, radiator, exhaust system, oil cooler and hoses, driveshaft, gearshift assembly, heat shields…the list goes on and on. And, of course, the engine and transmission.
The only snag was the transmission mount. One of the four mounting holes in the body didn’t align with the mount itself.
I can try to recall more detail if needed. It was a time consuming project but not difficult, as it’s essentially just removing 6 cylinder parts and installing V12 parts.
Personally I wouldn’t consider this swap without a donor car
I have someone’s half started abandoned XJ6C to XJ12C (series 1 Daimler mash up) project lingering in the barn. My hope is to use an 83 XJS as the parts source. The more I looked into specifics the more feasible it all became.
Doug - thanks for that - I do have the ECU but not the ECU harness. Some of the items you mentioned I had thought would have been common - like the radiator, gearshift etc but clearly not but I agree a cheap V12 4 door as a parts car would be a great help.
Cheers
Garry
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
10
For the years you’re looking at, I guess they did. Dunno if they both used the same mounting bolt and dowel pattern; Jaguar tended to be weird about such things.
Thanks for the comments - a bit more complex than I expected but not so much a big issue. I will keep my eye out for a suitable car but if nothing shows up the conversion route is always an option.
I did the reverse, put a 4.2 in my S1 V12. Had a donor car. Bizarre things needed changing, like horns. Power steering pump on different side. Road springs, ignition, tacho circuit operation, fuel lines, exhaust. A donor car would be a definite requirement. As I recall, transmission mount, driveshaft were the same, but, of course , both were SWB cars using BW12. Also, both were carburetted, so pumps were ok. Would be reasonably straightforward except for fuel injection complications.
is your 12 cylinder engine the early carbed version or the later fuel injected? If fuel injected you’ll have to address the return lines to the tanks including a swap of the tanks. As Doug wrote, it might be worth the while to purchase another 12 cylinder sedan - maybe cheap because of busted engine - as a donor car for the periphery parts.
Thanks my engine is fuel injected and I understand all XJC5.3s were injected.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
16
Do you care? You’re not planning to pass this thing off as an original XJ12C, are you? If you just want a nice XJ12C, you can start with an XJ6C and swap in whichever V12 you choose, including an earlier carb engine or a later Digital P H.E. or even better a much later 6.0.
… certainly not a straight swap - but with a carbed engine you’d only need the front half of a donor car, with a FI car you need the rear half as well:-)
Just wanted to point out you also have to swap both tanks - an operation that has cost many good XJs’ lives in the past.
Good luck
Jochen
75 XJ6L 4.2 auto (UK spec)
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
18
FI has a return line to the tanks, regular SII tanks (for non fuel injected engines) don’t, and the tanks differ depending on return line. David Boger has pics of the different tanks.
But, you’re right, my impression was based on this information, not on own experience.
Best
Jochen
75 XJ6L 4.2 auto (UK spec)
Jochen
75
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
20