You shouldn't have a problem with size and fit, if that's what you're wondering. The main thing will be to make sure the electrical system (EGR system, fuel injection system, etc) will be able to be swapped, and the cooling system is up to par.

The fuel injection system for the V12s was designed for that...not for a V6, and vice versa. Check out the electrical diagrams of the V12 versus the V6, and you'll see what I mean. The ECU (electrical control unit) of the XJ12s controlled each one of the injectors of the engine, so you would have to swap those (the ECU), as well as the EGR (exhaust gas recirculation) control unit (both located in the trunk). You MIGHT (not certain) have to swap out the fuel pumps and fuel pressure regulators (since you would, essentially, have more fuel running to the rail with a V12 than a V6).

Then, you have the cooling thing. You'd need to make sure the cooling system of your XJ6 would handle the V12 (it creates a LOT more heat than a V6). Probably would want to take the cooling system from an XJ12 and put it in.

Anyway, I've never done it, but I know the older Jags (I have a 76 XJ12 with a Chevy 350 in it), and I'm learning more and more every day. I'm guessing it would be a lot easier to stick a 350 in it, add the wiring harness that needs to be added, and call it a day.

 

Right. Setting the engine (and transmission) in place will be the easy part. Sorting out all the small details is what will take the most time and effort.

Do you still have the donor car that the V12 came from? It would be a big help as you can literally put the two cars side-by-side and swap over every part you need.

Cheers
DD

 

One correction the 4.2 is a straight 6.
As stated above it is doable but not just a straight drop in job.

Apart from all the electronics involved with the V12 do you also have the gearbox, because I believe that the two cars have different G/boxes.

Doubt that cooling is going to be too much of an issue in your location.

Personally, if your 4.2 is running OK, leave it where it is. The time and money involved with this conversion, compared to the overall value of the car, both before and after the job is just not viable.

And that V12 drinks petrol for fun.

 

That's true, too...thanks Rich. I forgot to mention that. The gear boxes AND the rear-ends (final drive ratio) are different between the two cars.

 

There's no such thing as "without too extreme an effort" where Jags are concerned...lol.

True, however, you'll have far less problems with the 350 than you would with the v12. My '76 has a V8 powerplant, and I love it. It sounds great, and I can actually work on the motor.

I'm unsure, but I can only guess yes. The EGR stuff had to be there for the injection system. I'm not sure where the control unit was. Unless someone else can answer this, your best bet is to browse a repair manual and find out.

 

Hello Nsander:

Hate to discourage but I must say it would be a waste of time. Much cheaper to just buy an XJ 12. You see from the responses there is a myriad of differences between the two. No one has pointed out the front suspension differences yet. The springs nee to be changed as well. This is a job that has been done succesfully before but it is really a mugs game.
If you have trouble with the 4.2 six the best solution is to fix it. With rexpects to motormouth my opinion of lumps is that they make no real sense at all and usually are created by people who don't know how to fix a Jaguar.
The only exception is if you blow up a V12 to the point where it is not repairable.
It is now upwards of $15000 to rebuild a V12 properly, but well under $4000 for a six, and the cost of putting in a Chev or a Ford motor ends up about the same as fixing the six at the end of it all.
And you don't end up with much in the way of improvements.
The worst thing about conversions are they are never done exactly right.
Best to fix and or hop up the six with some specialty performance parts then at least you still have a Jag.

I am usually cheery and encouraging but with this one, I am afraid not.

Hopefully my good friend Motor mouth will still be kind to me.
I have in fact taken a picture of his lovely white car onto my Jaguar Screensaver.


Good luck with what you decide, JustV12.

P.S. to Motormouth: Fix that chevy motor!
Can't be all that serious it is a chevy after all. The worlds stoutest and strongest V8!

 

Just to add that the V12 autogearbox is a GM400 not the Borg-Warner of the 6, and means the propshaft will probably be a different length as well. Rear axle ratio may also be different.

What you are proposing is a BIG job !!